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166-481: The T-maze is one of a group of various mazes of differing sizes and many shapes. It is one of the most simple, consisting of just two turns – right or left. The maze is only able to be altered by blocking one of the two paths. The basis behind the T-maze is to place the rat at the base of the maze. By placing a reward at one arm or both arms of the maze, the rat must make the choice of which path to take. The decision made by

332-418: A model system for studying neurophysiology . The form of neural plasticity known as long-term potentiation (LTP) was initially discovered to occur in the hippocampus and has often been studied in this structure. LTP is widely believed to be one of the main neural mechanisms by which memories are stored in the brain. In rodents as model organisms , the hippocampus has been studied extensively as part of

498-457: A multiple-systems model , suggesting that some effects may not be simply mediated by one portion of the brain. Studies on freely moving rats and mice have shown many hippocampal neurons to act as place cells that cluster in place fields , and these fire bursts of action potentials when the animal passes through a particular location. This place-related neural activity in the hippocampus has also been reported in monkeys that were moved around

664-414: A brain system responsible for spatial memory and navigation. Many neurons in the rat and mouse hippocampus respond as place cells : that is, they fire bursts of action potentials when the animal passes through a specific part of its environment. Hippocampal place cells interact extensively with head direction cells , whose activity acts as an inertial compass, and conjecturally with grid cells in

830-418: A broader system that incorporates both the memory and the spatial perspectives in its role that involves the use of a wide scope of cognitive maps. This relates to the purposive behaviorism born of Tolman's original goal of identifying the complex cognitive mechanisms and purposes that guided behaviour. It has also been proposed that the spiking activity of hippocampal neurons is associated spatially, and it

996-633: A candidate mechanism for long-term memory , LTP has since been studied intensively, and a great deal has been learned about it. However, the complexity and variety of the intracellular signalling cascades that can trigger LTP is acknowledged as preventing a more complete understanding. The hippocampus is a particularly favorable site for studying LTP because of its densely packed and sharply defined layers of neurons, but similar types of activity-dependent synaptic change have also been observed in many other brain areas. The best-studied form of LTP has been seen in CA1 of

1162-418: A comparison with the shape of the folded back forelimbs and webbed feet of the mythological hippocampus , a sea monster with a horse's forequarters and a fish's tail. The hippocampus was then described as pes hippocampi major , with an adjacent bulge in the occipital horn , described as the pes hippocampi minor and later renamed as the calcar avis . The renaming of the hippocampus as hippocampus major, and

1328-496: A default...(which) modulated according to...task demands." Psychologists also think that cognitive maps are instance based, which accounts for "discriminative matching to past experience." This field has traditionally been hampered by confounding variables, such as cost and the potential for previous exposure to an experimental environment. Technological advancements, including those in virtual reality technology, have made findings more accessible. Virtual reality affords experimenters

1494-529: A distinct pattern of neural population activity and waves of electrical activity as measured by an electroencephalogram (EEG). These modes are named after the EEG patterns associated with them: theta and large irregular activity (LIA). The main characteristics described below are for the rat, which is the animal most extensively studied. The theta mode appears during states of active, alert behavior (especially locomotion), and also during REM (dreaming) sleep. In

1660-417: A familiar city. Spatial memories are said to form after a person has already gathered and processed sensory information about her or his environment. Working memory (WM) can be described as a limited capacity system that allows one to temporarily store and process information. This temporary store enables one to complete or work on complex tasks while being able to keep information in mind. For instance,

1826-540: A feature that people are biased towards when relating to space; for example, one axial line determinant is gravity (McNamara & Shelton, 2001; Kim & Penn, 2004). Axial lines aid everyone in apportioning our perceptions into regions. This parceled world idea is further supported by the finding that items that get recalled together are more likely than not to also be clustered within the same region of one's larger cognitive map. Clustering shows that people tend to chunk information together according to smaller layouts within

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1992-417: A full-fledged theory of the role of the hippocampus in anxiety. The inhibition theory is currently the least popular of the three. The second major line of thought relates the hippocampus to memory. Although it had historical precursors, this idea derived its main impetus from a famous report by American neurosurgeon William Beecher Scoville and British-Canadian neuropsychologist Brenda Milner describing

2158-449: A hidden goal. Other cells have been discovered since the finding of the place cells in the rodent brain that are either in the hippocampus or the entorhinal cortex. These have been assigned as head direction cells , grid cells and boundary cells . Speed cells are thought to provide input to the hippocampal grid cells. Approach-avoidance conflict happens when a situation is presented that can either be rewarding or punishing, and

2324-402: A larger cognitive map. Boundaries are not the only determinants of layout. Clustering also demonstrates another important property of relation to spatial conceptions, which is that spatial recall is a hierarchical process. When someone recalls an environment or navigates terrain, that person implicitly recalls the overall layout at first. Then, due to the concept's "rich correlational structure",

2490-405: A life-long memory of the event even after a single training session. The memory of such an event appears to be first stored in the hippocampus, but this storage is transient. Much of the long-term storage of the memory seems to take place in the anterior cingulate cortex . When such an intense learning event was experimentally applied, more than 5,000 differently methylated DNA regions appeared in

2656-474: A line of work that eventually led to their very influential 1978 book The Hippocampus as a Cognitive Map . There is now almost universal agreement that hippocampal function plays an important role in spatial coding, but the details are widely debated. Later research has focused on trying to bridge the disconnect between the two main views of hippocampal function as being split between memory and spatial cognition. In some studies, these areas have been expanded to

2822-491: A more efficient way. An interesting study investigating taxi drivers' memory for streets in Helsinki , Finland , examined the role of prelearned spatial knowledge. This study compared experts to a control group to determine how this prelearned knowledge in their skill domain allows them to overcome the capacity limitations of STM and WM. The study used four levels of spatial randomness: The results of this study indicate that

2988-488: A multiple T-maze was performed by allowing the rat to explore the multiple T-maze without a reward. After letting the rat roam, researchers restarted the maze again with a reward placed at the end of the maze. The rats with prior exposure to the maze were able to easily navigate through the maze to reach the reward. This experiment proved that rats have the ability to generate a cognitive map when exposed to their surroundings and can process this information when needed to complete

3154-420: A need for a sudden detour on a long road trip. Lack of experience in a locale, or simply sheer size, can disorient one's mental layout, especially in a large and unfamiliar place with many overwhelming stimuli. In these environments, people are still able to orient themselves, and find their way around using landmarks. This ability to "prioritize objects and regions in complex scenes for selection (and) recognition"

3320-415: A number of studies that show the involvement of the hippocampus in conflict tasks. The authors suggest that one challenge is to understand how conflict processing relates to the functions of spatial navigation and memory and how all of these functions need not be mutually exclusive. The hippocampus has received renewed attention for its role in social memory. Epileptic human subjects with depth electrodes in

3486-400: A number of variables, such as the type of food hidden, the locations where the food is hidden, the retention interval, as well as any odor cues that could skew results of memory research. Studies have indicated that rats have memory for where they have hidden food and what type of food they have hidden. This is shown in retrieval behavior, such that the rats are selective in going more often to

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3652-418: A pathway from the opening of the maze to the drawing of the man. The participant is then expected to replicate the demonstrated pathway through the maze to the drawing of the man. Mazes vary in complexity as difficulty increases. First pioneered by Olton and Samuelson in 1976, the radial arm maze is designed to test the spatial memory capabilities of rats. Mazes are typically designed with a center platform and

3818-511: A proportion of the claimed CA1 cells in the study. The dorsal CA2 and ventral CA1 subregions of the hippocampus have been implicated in social memory processing. Genetic inactivation of CA2 pyramidal neurons leads to pronounced loss of social memory, while maintaining intact sociability in mice. Similarly, ventral CA1 pyramidal neurons have also been demonstrated as critical for social memory under optogenetic control in mice. The hippocampus shows two major "modes" of activity, each associated with

3984-411: A rat's location to be reconstructed with high confidence. The size of place fields varies in a gradient along the length of the hippocampus, with cells at the dorsal end showing the smallest fields, cells near the center showing larger fields, and cells at the ventral tip showing fields that cover the entire environment. In some cases, the firing rate of hippocampal cells depends not only on place but also

4150-531: A result of depression, but this can be stopped with anti-depressants even if they are not effective in relieving other symptoms. Chronic stress resulting in elevated levels of glucocorticoids , notably of cortisol , is seen to be a cause of neuronal atrophy in the hippocampus. This atrophy results in a smaller hippocampal volume which is also seen in Cushing's syndrome . The higher levels of cortisol in Cushing's syndrome

4316-579: A room whilst in a restraint chair. However, the place cells may have fired in relation to where the monkey was looking rather than to its actual location in the room. Over many years, many studies have been carried out on place-responses in rodents, which have given a large amount of information. Place cell responses are shown by pyramidal cells in the hippocampus and by granule cells in the dentate gyrus . Other cells in smaller proportion are inhibitory interneurons , and these often show place-related variations in their firing rate that are much weaker. There

4482-486: A series of associations become activated. Eventually, the resulting cascade of activations will awaken the particular details that correspond with the region being recalled. This is how people encode many entities from varying ontological levels, such as the location of a stapler; in a desk; which is in the office. One can recall from only one region at a time (a bottleneck). A bottleneck in a person's cognitive navigational system could be an issue. For instance, if there were

4648-477: A severe impact on many types of cognition including memory . Even normal aging is associated with a gradual decline in some types of memory, including episodic memory and working memory (or short-term memory ). Because the hippocampus is thought to play a central role in memory, there has been considerable interest in the possibility that age-related declines could be caused by hippocampal deterioration. Some early studies reported substantial loss of neurons in

4814-444: A sharp wave, there is a dramatic increase in firing rate in up to 10% of the hippocampal population These two hippocampal activity modes can be seen in primates as well as rats, with the exception that it has been difficult to see robust theta rhythmicity in the primate hippocampus. There are, however, qualitatively similar sharp waves and similar state-dependent changes in neural population activity. The underlying currents producing

4980-477: A system allowing one to temporarily store and manage information that is necessary to complete complex cognitive tasks. Tasks which employ short-term memory include learning , reasoning , and comprehension. Spatial memory is a cognitive process that enables a person to remember different locations as well as spatial relations between objects. This allows one to remember where an object is in relation to another object; for instance, allowing someone to navigate in

5146-478: A task. Researchers have also created the Y-maze which functions very similar to the T-maze. The Y-maze is altered to have a more gradual change into the arms. The arms are also all equal in length and distance apart from one another. The Y-maze has proven to be easier for rats to understand the layout of the space and recognize rewards, similar pattern, and adapt to new experiments at a quicker pace. The radial arm maze

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5312-400: A topographically organized map of the spatial environment made up of grid cells . This brain region thus transforms sensory input from the environment and stores it as a durable allocentric representation in the brain to be used for path integration . Hippocampus The hippocampus ( pl. : hippocampi ; via Latin from Greek ἱππόκαμπος , ' seahorse ') is a major component of

5478-402: A varying number of arms branching off with food placed at the ends. The arms are usually shielded from each other in some way but not to the extent that external cues cannot be used as reference points. In most cases, the rat is placed in the center of the maze and needs to explore each arm individually to retrieve food while simultaneously remembering which arms it has already pursued. The maze

5644-610: A very irregular temporal pattern. Sharp waves are less frequent during inactive waking states and are usually smaller. Sharp waves have also been observed in humans and monkeys. In macaques, sharp waves are robust but do not occur as frequently as in rats. One of the most interesting aspects of sharp waves is that they appear to be associated with memory. Wilson and McNaughton 1994, and numerous later studies, reported that when hippocampal place cells have overlapping spatial firing fields (and therefore often fire in near-simultaneity), they tend to show correlated activity during sleep following

5810-438: A way that is difficult to code verbally, forcing the participant to rely on visual spatial memory. Beginning with a small 2 x 2 matrix, participants copy the matrix pattern from memory into an empty matrix. The matrix patterns are increased in size and complexity at a rate of two cells until the participant's ability to replicate them breaks down. On average, participants' performance tends to break down at sixteen cells. This task

5976-444: A working memory but not on a short-term memory task was affected by articulatory suppression suggesting that impairment on the spatial task was caused by the concurrent performance on a task that had extensive use of executive resources. Results have also found that performances were impaired on STM and WM tasks with executive suppression. This illustrates how, within the visuo-spatial domain, both STM and WM require similar utility of

6142-529: Is "a mental model of objects' spatial configuration that permits navigation along optimal path between arbitrary pairs of points." This mental map is built upon two fundamental bedrocks: layout, also known as route knowledge, and landmark orientation. Layout is potentially the first method of navigation that people learn to utilize; its workings reflect our most basic understandings of the world. Hermer and Spelke (1994) determined that when toddlers begin to walk, around eighteen months, they navigate by their sense of

6308-474: Is a top-down procedure that requires an individual to recall the superordinate features of a cognitive map, followed by the ordinate and subordinate features. Two spatial features are prominent in navigating a path: general layout and landmark orienting (Kahana et al., 2006). People are not only capable of learning about the spatial layout of their surroundings, but they can also piece together novel routes and new spatial relations through inference. A cognitive map

6474-462: Is also substantial evidence that it makes a contribution to memory, which can be distinguished from the contribution of the hippocampus. It is apparent that complete amnesia occurs only when both the hippocampus and the parahippocampus are damaged. The major input to the hippocampus is through the entorhinal cortex (EC), whereas its major output is via CA1 to the subiculum. Information reaches CA1 via two main pathways, direct and indirect. Axons from

6640-413: Is concealed by the parahippocampal gyrus . The cortex thins from six layers to the three or four layers that make up the hippocampus. The term hippocampal formation is used to refer to the hippocampus proper and its related parts. However, there is no consensus as to what parts are included. Sometimes the hippocampus is said to include the dentate gyrus and the subiculum . Some references include

6806-487: Is constructed of a high number of T-junctions. Each intersection remains the same length and scale, which gives every point within the maze a direct right or wrong answer. By not changing the size of the maze, it allows for the rat to focus on the decision and not be confused if the size of the maze was altered within the junctions. Multiple T-mazes are constructed to question response vs. place techniques and of cognitive direction and mapping. An example of an experiment within

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6972-424: Is constructed with a center platform with arms radiating from the center. The original maze had 8 spokes, but they have been constructed with as few as 3 and as many as 48 spokes. This type of maze is used to perform short-term memory experimentations on rats. Rats are examined on whether or not they have the ability to remember the arms they have already explored. This is determined by placing food pellets at each of

7138-399: Is described as having an anterior and posterior part (in primates ) or a ventral and dorsal part in other animals. Both parts are of similar composition but belong to different neural circuits . In the rat, the two hippocampi resemble a pair of bananas, joined at the stems by the commissure of fornix (also called the hippocampal commissure). In primates , the part of the hippocampus at

7304-461: Is designed to measure spatial memory abilities in children. The experimenter asks the participant to visualize a blank matrix with a little man. Through a series of directional instructions such as forwards, backwards, left or right, the experimenter guides the participant's little man on a pathway throughout the matrix. At the end, the participant is asked to indicate on a real matrix where the little man that he or she visualized finished. The length of

7470-441: Is found through experiments using the dual-task paradigm . A number of studies have shown that the retention of visual shapes or colors (i.e., visual information) is disrupted by the presentation of irrelevant pictures or dynamic visual noise. Conversely, the retention of location (i.e., spatial information) is disrupted only by spatial tracking tasks, spatial tapping tasks, and eye movements. For example, participants completed both

7636-421: Is important for long-term spatial memory of allocentric space (reference to external cues in space). Maintenance and retrieval of memories are thus relational or context dependent . The hippocampus makes use of reference and working memory and has the important role of processing information about spatial locations. Blocking plasticity in this region results in problems in goal-directed navigation and impairs

7802-441: Is known to contain two separate memory circuits. One circuit is used for recollection-based place recognition memory and includes the entorhinal-CA1 system , while the other system, consisting of the hippocampus trisynaptic loop (entohinal-dentate-CA3-CA1) is used for place recall memory and facilitation of plasticity at the entorhinal-dentate synapse in mice is sufficient to enhance place recall. Place cells are also found in

7968-437: Is little, if any, spatial topography in the representation; in general, cells lying next to each other in the hippocampus have uncorrelated spatial firing patterns. Place cells are typically almost silent when a rat is moving around outside the place field but reach sustained rates as high as 40 Hz when the rat is near the center. Neural activity sampled from 30 to 40 randomly chosen place cells carries enough information to allow

8134-412: Is located in the medial temporal lobe area of the brain and is responsible for governing spatial memory. In animals, this allows them to have a spatial map of their environment and it uses reference and working memory to accomplish this. It also has important functions that govern long and short-term memory as well as spatial navigation, both of which are required in order for the rat to correctly navigate

8300-458: Is not yet clear. In rats (the animals that have been the most extensively studied), theta is seen mainly in two conditions: first, when an animal is walking or in some other way actively interacting with its surroundings; second, during REM sleep . The function of theta has not yet been convincingly explained although numerous theories have been proposed. The most popular hypothesis has been to relate it to learning and memory. An example would be

8466-516: Is occasionally interrupted by large surges called sharp waves . These events are associated with bursts of spike activity lasting 50 to 100 milliseconds in pyramidal cells of CA3 and CA1. They are also associated with short-lived high-frequency EEG oscillations called "ripples", with frequencies in the range 150 to 200 Hz in rats, and together they are known as sharp waves and ripples . Sharp waves are most frequent during sleep when they occur at an average rate of around 1 per second (in rats) but in

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8632-445: Is partly why returning to a location where an emotional event occurred may evoke that emotion. There is a deep emotional connection between episodic memories and places. Due to bilateral symmetry the brain has a hippocampus in each cerebral hemisphere . If damage to the hippocampus occurs in only one hemisphere, leaving the structure intact in the other hemisphere, the brain can retain near-normal memory functioning. Severe damage to

8798-675: Is related to the anterior parts of the right and left hippocampus. The right head of the hippocampus is more involved in executive functions and regulation during verbal memory recall. The tail of the left hippocampus tends to be closely related to verbal memory capacity. Damage to the hippocampus does not affect some types of memory, such as the ability to learn new skills (playing a musical instrument or solving certain types of puzzles, for example). This fact suggests that such abilities depend on different types of memory ( procedural memory ) and different brain regions. Furthermore, amnesic patients frequently show "implicit" memory for experiences even in

8964-405: Is required for retrieval, processing short-term memory and transferring memory from the short term to longer delay periods. Infusion of amphetamine into the dorsal hippocampus has also been shown to enhance memory for spatial locations learned previously. These findings indicate that there is a functional dissociation between the dorsal and ventral hippocampus. Hemispheric differences within

9130-451: Is required to decrease the stress levels of the animal. The stress of the animal may impair cognitive testing results. The hippocampus provides animals with a spatial map of their environment. It stores information regarding non-egocentric space (egocentric means in reference to one's body position in space) and therefore supports viewpoint independence in spatial memory. This means that it allows for viewpoint manipulation from memory. It

9296-539: Is required to navigate in a familiar city. A rat's spatial memory is needed to learn the location of food at the end of a maze . In both humans and animals, spatial memories are summarized as a cognitive map . Spatial memory has representations within working, short-term memory and long-term memory . Research indicates that there are specific areas of the brain associated with spatial memory. Many methods are used for measuring spatial memory in children, adults, and animals. Short-term memory (STM) can be described as

9462-412: Is resistant to recognition of a learned platform task only when the entire hippocampus is lesioned, but not when it is partially lesioned. Deficits in spatial memory are also found in spatial discrimination tasks. Large differences in spatial impairment are found among the dorsal and ventral hippocampus. Lesions to the ventral hippocampus have no effect on spatial memory, while the dorsal hippocampus

9628-472: Is responsible for information about locations and movement (i.e., where). This distinction is not always straightforward since part of visual memory involves spatial information and vice versa. For example, memory for object shapes usually involves maintaining information about the spatial arrangement of the features which define the object in question. In practice, the two systems work together in some capacity but different tasks have been developed to highlight

9794-424: Is seen among allocentric tasks. Rats with lesions to the anterior region of the posterior parietal cortex reexplore displaced objects, while rats with lesions to the posterior region of the posterior parietal cortex displayed no reaction to spatial change. Parietal cortex lesions are also known to produce temporally ungraded retrograde amnesia . The dorsalcaudal medial entorhinal cortex (dMEC) contains

9960-416: Is set up so the rat is forced to return to the center of the maze before pursuing another arm. Measures are usually taken to prevent the rat from using its olfactory senses to navigate such as placing extra food throughout the bottom of the maze. The Morris water navigation task is a classic test for studying spatial learning and memory in rats and was first developed in 1981 by Richard G. Morris for whom

10126-401: Is suggested that the memory, spatial cognition, and conflict processing functions may be seen as working together and not mutually exclusive. Psychologists and neuroscientists generally agree that the hippocampus plays an important role in the formation of new memories about experienced events ( episodic or autobiographical memory ). Part of this function is hippocampal involvement in

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10292-447: Is usually the result of medications taken for other conditions. Neuronal loss also occurs as a result of impaired neurogenesis. Another factor that contributes to a smaller hippocampal volume is that of dendritic retraction where dendrites are shortened in length and reduced in number, in response to increased glucocorticoids. This dendritic retraction is reversible. After treatment with medication to reduce cortisol in Cushing's syndrome,

10458-541: The Great Hippocampus Question . The term hippocampus minor fell from use in anatomy textbooks and was officially removed in the Nomina Anatomica of 1895. Today, the structure is just called the hippocampus, with the term cornu Ammonis (that is, 'Ammon's horn') surviving in the names of the hippocampal subfields CA1-CA4 . The term limbic system was introduced in 1952 by Paul MacLean to describe

10624-413: The brain of humans and other vertebrates . Humans and other mammals have two hippocampi, one in each side of the brain . The hippocampus is part of the limbic system , and plays important roles in the consolidation of information from short-term memory to long-term memory , and in spatial memory that enables navigation. The hippocampus is located in the allocortex , with neural projections into

10790-423: The entorhinal cortex via the perforant path . The entorhinal cortex (EC) is strongly and reciprocally connected with many cortical and subcortical structures as well as with the brainstem. Different thalamic nuclei , (from the anterior and midline groups), the medial septal nucleus , the supramammillary nucleus of the hypothalamus, and the raphe nuclei and locus coeruleus of the brainstem all send axons to

10956-475: The hypothalamic mammillary body , and the anterior nuclear complex in the thalamus , and is generally accepted to be part of the limbic system. The hippocampus can be seen as a ridge of gray matter tissue , elevating from the floor of each lateral ventricle in the region of the inferior or temporal horn. This ridge can also be seen as an inward fold of the archicortex into the medial temporal lobe . The hippocampus can only be seen in dissections as it

11122-479: The neocortex , in humans as well as other primates. The hippocampus, as the medial pallium , is a structure found in all vertebrates . In humans, it contains two main interlocking parts: the hippocampus proper (also called Ammon's horn ), and the dentate gyrus . In Alzheimer's disease (and other forms of dementia ), the hippocampus is one of the first regions of the brain to suffer damage; short-term memory loss and disorientation are included among

11288-474: The thalamus to field CA1. A very important projection comes from the medial septal nucleus, which sends cholinergic , and gamma amino butyric acid (GABA) stimulating fibers (GABAergic fibers) to all parts of the hippocampus. The inputs from the medial septal nucleus play a key role in controlling the physiological state of the hippocampus; destruction of this nucleus abolishes the hippocampal theta rhythm and severely impairs certain types of memory. Areas of

11454-527: The Corsi Blocks Task relates primarily to spatial working memory. There are a variety of tasks psychologists use to measure spatial memory on adults, children and animal models. These tasks allow professionals to identify cognitive irregularities in adults and children and allows researchers to administer varying types of drugs and/or lesions in participants and measure the consequential effects on spatial memory. The Corsi block-tapping test, also known as

11620-469: The Corsi span rest, is a psychological test commonly used to determine the visual-spatial memory span and the implicit visual-spatial learning abilities of an individual. Participants sit with nine wooden 3x3-cm blocks fastened before them on a 25- x 30-cm baseboard in a standard random order. The experiment taps onto the blocks a sequence pattern which participants must then replicate. The blocks are numbered on

11786-507: The DH were shown to cause spatial memory impairment while VH lesions did not. Its projecting pathways include the medial septal nucleus and supramammillary nucleus . The dorsal hippocampus also has more place cells than both the ventral and intermediate hippocampal regions. The intermediate hippocampus has overlapping characteristics with both the ventral and dorsal hippocampus. Using anterograde tracing methods, Cenquizca and Swanson (2007) located

11952-510: The DNA base excision repair pathway (see Epigenetics in learning and memory ). The between-systems memory interference model describes the inhibition of non-hippocampal systems of memory during concurrent hippocampal activity. Specifically, Fraser Sparks, Hugo Lehmann, and Robert Sutherland found that when the hippocampus was inactive, non-hippocampal systems located elsewhere in the brain were found to consolidate memory in its place. However, when

12118-448: The EC that originate in layer III are the origin of the direct perforant pathway and form synapses on the very distal apical dendrites of CA1 neurons. Conversely, axons originating from layer II are the origin of the indirect pathway, and information reaches CA1 via the trisynaptic circuit . In the initial part of this pathway, the axons project through the perforant pathway to the granule cells of

12284-403: The EC, so that it serves as the interface between the neocortex and the other connections, and the hippocampus. The EC is located in the parahippocampal gyrus , a cortical region adjacent to the hippocampus. This gyrus conceals the hippocampus. The parahippocampal gyrus is adjacent to the perirhinal cortex , which plays an important role in the visual recognition of complex objects. There

12450-498: The LIA mode, the EEG is dominated by sharp waves that are randomly timed large deflections of the EEG signal lasting for 25–50 milliseconds. Sharp waves are frequently generated in sets, with sets containing up to 5 or more individual sharp waves and lasting up to 500 ms. The spiking activity of neurons within the hippocampus is highly correlated with sharp wave activity. Most neurons decrease their firing rate between sharp waves; however, during

12616-459: The University of Maryland compared the effect of different levels of immersion on spatial memory recall. In the study, 40 participants used both a traditional desktop and a head-mounted display to view two environments, a medieval town, and an ornate palace, where they memorized two sets of 21 faces presented as 3D portraits. After viewing these 21 faces for 5 minutes, followed by a brief rest period,

12782-500: The VPT and the Corsi Blocks Task in a selective interference experiment. During the retention interval of the VPT, the subject viewed irrelevant pictures (e.g., avant-garde paintings). The spatial interference task required participants to follow, by touching the stimuli, an arrangement of small wooden pegs which were concealed behind a screen. Both the visual and spatial spans were shortened by their respective interference tasks, confirming that

12948-510: The ability to remember precise locations. Amnesic patients with damage to the hippocampus cannot learn or remember spatial layouts, and patients having undergone hippocampal removal are severely impaired in spatial navigation. Monkeys with lesions to this area cannot learn object-place associations and rats also display spatial deficits by not reacting to spatial change. In addition, rats with hippocampal lesions were shown to have temporally ungraded (time-independent) retrograde amnesia that

13114-464: The ability to work on a complicated mathematical problem utilizes one's working memory. One influential theory of WM is the Baddeley and Hitch multi-component model of working memory . The most recent version of this model suggests that there are four subcomponents to WM: phonological loop , the visuo-spatial sketchpad , the central executive , and the episodic buffer . One component of this model,

13280-481: The absence of conscious knowledge. For example, patients asked to guess which of two faces they have seen most recently may give the correct answer most of the time in spite of stating that they have never seen either of the faces before. Some researchers distinguish between conscious recollection , which depends on the hippocampus, and familiarity , which depends on portions of the medial temporal lobe. When rats are exposed to an intense learning event, they may retain

13446-432: The ancient Egyptian god often portrayed as such takes the name c ornu A mmonis . Its abbreviation CA is used in naming the hippocampal subfields CA1, CA2, CA3, and CA4 . It can be distinguished as an area where the cortex narrows into a single layer of densely packed pyramidal neurons , which curl into a tight U shape. One edge of the "U," – CA4, is embedded into the backward-facing, flexed dentate gyrus. The hippocampus

13612-438: The arms and the rat must only travel down each arm once and retrieve the pellet accordingly. The concepts of T-mazes are used to assess rodent behavior. The different tasks such as left-right discrimination and forced alternation are mainly used with rodents to test reference and working memory. Maze research is used to show how the rodent's behavior evolves with alternate strategies to do different tasks. The spatial memory of

13778-461: The arms of the maze where they have previously hidden preferred food than to arms with less preferred food or where no food was hidden. The evidence for the spatial memory of some species of animals, such as rats, indicates that they do use spatial memory to locate and retrieve hidden food stores. A study using GPS tracking to see where domestic cats go when their owners let them outside reported that cats have substantial spatial memory. Some of

13944-493: The behavioral session. This enhancement of correlation, commonly known as reactivation , has been found to occur mainly during sharp waves. It has been proposed that sharp waves are, in fact, reactivations of neural activity patterns that were memorized during behavior, driven by strengthening of synaptic connections within the hippocampus. This idea forms a key component of the "two-stage memory" theory, advocated by Buzsáki and others, which proposes that memories are stored within

14110-428: The bottom, near the base of the temporal lobe , is much broader than the part at the top. This means that in cross-section the hippocampus can show a number of different shapes, depending on the angle and location of the cut. In a cross-section of the hippocampus, including the dentate gyrus, several layers will be shown. The dentate gyrus has three layers of cells (or four if the hilus is included). The layers are from

14276-417: The brain that are either in the hippocampus itself or are strongly connected to it, such as the speed cells present in the medial entorhinal cortex . Together these cells form a network that serves as spatial memory. The first of such cells discovered in the 1970s were the place cells, which led to the idea of the hippocampus acting to give a neural representation of the environment in a cognitive map . When

14442-470: The brakes!") was very popular up to the 1960s. It derived much of its justification from two observations: first, that animals with hippocampal damage tend to be hyperactive ; second, that animals with hippocampal damage often have difficulty learning to inhibit responses that they have previously been taught, especially if the response requires remaining quiet as in a passive avoidance test. British psychologist Jeffrey Gray developed this line of thought into

14608-441: The calcar avis as hippocampus minor, has been attributed to Félix Vicq-d'Azyr systematizing nomenclature of parts of the brain in 1786. Mayer mistakenly used the term hippopotamus in 1779, and was followed by some other authors until Karl Friedrich Burdach resolved this error in 1829. In 1861 the hippocampus minor became the center of a dispute over human evolution between Thomas Henry Huxley and Richard Owen , satirized as

14774-400: The cats in the study demonstrated exceptional long term spatial memory. One of them, usually traveling no further than 200 m (660 ft) to 250 m (820 ft) from its home, unexpectedly traveled some 1,250 m (4,100 ft) from its home. Researchers initially thought this to be a GPS malfunction, but soon discovered that the cat's owners went out of town that weekend, and that

14940-482: The central executive is intimately involved in a number of spatial tasks, the exact way in which they are connected remains to be seen. Spatial memory recall is built upon a hierarchical structure . People remember the general layout of a particular space and then "cue target locations" within that spatial set. This paradigm includes an ordinal scale of features that an individual must attend to in order to inform his or her cognitive map. Recollection of spatial details

15106-543: The central executive. Additionally, during a spatial visualisation task (which is related to executive functioning and not STM or WM) concurrent executive suppression impaired performance indicating that the effects were due to common demands on the central executive and not short-term storage. The researchers concluded with the explanation that the central executive employs cognitive strategies enabling participants to both encode and maintain mental representations during short-term memory tasks. Although studies suggest that

15272-411: The comments made by the experts during the procedure point towards their use of route knowledge in completing the task. To ensure that it was in fact spatial information that they were encoding, the researchers also presented lists in alphabetical order and semantic categories. However, the researchers found that it was in fact spatial information that the experts were chunking, allowing them to surpass

15438-471: The dentate gyrus (first synapse). From then, the information follows via the mossy fibres to CA3 (second synapse). From there, CA3 axons called Schaffer collaterals leave the deep part of the cell body and loop up to the apical dendrites and then extend to CA1 (third synapse). Axons from CA1 then project back to the entorhinal cortex, completing the circuit. Basket cells in CA3 receive excitatory input from

15604-404: The dentate gyrus and the subiculum in the hippocampal formation, and others also include the presubiculum, parasubiculum , and entorhinal cortex . The neural layout and pathways within the hippocampal formation are very similar in all mammals. The hippocampus, including the dentate gyrus, has the shape of a curved tube, which has been compared to a seahorse, and to a horn of a ram, which after

15770-412: The detection of new events, places and stimuli. Some researchers regard the hippocampus as part of a larger medial temporal lobe memory system responsible for general declarative memory (memories that can be explicitly verbalized – these would include, for example, memory for facts in addition to episodic memory). The hippocampus also encodes emotional context from the amygdala . This

15936-410: The direction a rat is moving, the destination toward which it is traveling, or other task-related variables. The firing of place cells is timed in relation to local theta waves , a process termed phase precession . In humans, cells with location-specific firing patterns have been reported during a study of patients with drug-resistant epilepsy . They were undergoing an invasive procedure to localize

16102-422: The earliest widely held hypothesis was that the hippocampus is involved in olfaction . This idea was cast into doubt by a series of anatomical studies that did not find any direct projections to the hippocampus from the olfactory bulb . However, later work did confirm that the olfactory bulb does project into the ventral part of the lateral entorhinal cortex, and field CA1 in the ventral hippocampus sends axons to

16268-412: The early symptoms. Damage to the hippocampus can also result from oxygen starvation ( hypoxia ), encephalitis , or medial temporal lobe epilepsy . People with extensive, bilateral hippocampal damage may experience anterograde amnesia : the inability to form and retain new memories . Since different neuronal cell types are neatly organized into layers in the hippocampus, it has frequently been used as

16434-443: The edge of the pool first before venturing out into the center in a meandering pattern before stumbling upon the hidden platform. However, as time spent in the pool increases experience, the amount of time needed to locate the platform decreases, with veteran rats swimming directly to the platform almost immediately after being placed in the water. Due to the nature of task involving rats to swim, most researchers believe that habituation

16600-480: The elderly than in the young. Furthermore, a randomized control trial published in 2011 found that aerobic exercise could increase the size of the hippocampus in adults aged 55 to 80 and also improve spatial memory. The hippocampus contains high levels of glucocorticoid receptors , which make it more vulnerable to long-term stress than most other brain areas . There is evidence that humans having experienced severe, long-lasting traumatic stress show atrophy of

16766-482: The ensuing decision-making has been associated with anxiety . fMRI findings from studies in approach-avoidance decision-making found evidence for a functional role that is not explained by either long-term memory or spatial cognition. Overall findings showed that the anterior hippocampus is sensitive to conflict, and that it may be part of a larger cortical and subcortical network seen to be important in decision-making in uncertain conditions. A review makes reference to

16932-510: The environment relative to their body, elements that are absent with the desktop, was key to their success. Within the literature, there is evidence that experts in a particular field are able to perform memory tasks in accordance with their skills at an exceptional level. The level of skill displayed by experts may exceed the limits of the normal capacity of both STM and WM. Because experts have an enormous amount of prelearned and task-specific knowledge, they may be able to encode information in

17098-454: The experimenters' side to allow for efficient pattern demonstration. The sequence length increases each trial until the participant is no longer able to replicate the pattern correctly. The test can be used to measure both short-term and long-term spatial memory, depending on the length of time between test and recall. The test was created by Canadian neuropsychologist Phillip Corsi, who modeled it after Hebb's digit span task by replacing

17264-406: The faces in the virtual environments were replaced with numbers, and participants recalled which face was at each location. The study found on average, those who used the head-mounted display recalled the faces 8.8% more accurately, and with a greater confidence. The participants state that leveraging their innate vestibular and proprioceptive senses with the head-mounted display and mapping aspects of

17430-407: The fastest routes between them in order to pass a strict test known as The Knowledge in order to gain a license to operate. A study showed that the posterior part of the hippocampus is larger in these drivers than in the general public, and that a positive correlation exists between the length of time served as a driver and the increase in the volume of this part. It was also found the total volume of

17596-514: The first to illustrate the structure, also wavered between "seahorse" and "silkworm". "Ram's horn" was proposed by the Danish anatomist Jacob Winsløw in 1732; and a decade later his fellow Parisian, the surgeon de Garengeot, used cornu Ammonis – horn of Amun , the ancient Egyptian god who was often represented as having a ram's head. Another reference appeared with the term pes hippocampi , which may date back to Diemerbroeck in 1672, introducing

17762-422: The hippocampi in both hemispheres results in profound difficulties in forming new memories ( anterograde amnesia ) and often also affects memories formed before the damage occurred ( retrograde amnesia ). Although the retrograde effect normally extends many years back before the brain damage, in some cases older memories remain. This retention of older memories leads to the idea that consolidation over time involves

17928-615: The hippocampus neuronal genome of the rats at one hour and at 24 hours after training. These alterations in methylation pattern occurred at many genes that were down-regulated , often due to the formation of new 5-methylcytosine sites in CpG rich regions of the genome. Furthermore, many other genes were upregulated , likely often due to the removal of methyl groups from previously existing 5-methylcytosines (5mCs) in DNA. Demethylation of 5mC can be carried out by several proteins acting in concert, including TET enzymes as well as enzymes of

18094-422: The hippocampus and occurs at synapses that terminate on dendritic spines and use the neurotransmitter glutamate . The synaptic changes depend on a special type of glutamate receptor , the N -methyl-D-aspartate (NMDA) receptor , a cell surface receptor which has the special property of allowing calcium to enter the postsynaptic spine only when presynaptic activation and postsynaptic depolarization occur at

18260-440: The hippocampus are also observed. A study on London taxi drivers, asked drivers to recall complex routes around the city as well as famous landmarks for which the drivers had no knowledge of their spatial location. This resulted in an activation of the right hippocampus solely during recall of the complex routes which indicates that the right hippocampus is used for navigation in large scale spatial environments. The hippocampus

18426-401: The hippocampus are shown to be functionally and anatomically distinct. The dorsal hippocampus (DH), ventral hippocampus (VH) and intermediate hippocampus serve different functions, project with differing pathways, and have varying degrees of place cells. The dorsal hippocampus serves for spatial memory, verbal memory, and learning of conceptual information. Using the radial arm maze , lesions in

18592-475: The hippocampus during behavior and then later transferred to the neocortex during sleep. Sharp waves in Hebbian theory are seen as persistently repeated stimulations by presynaptic cells, of postsynaptic cells that are suggested to drive synaptic changes in the cortical targets of hippocampal output pathways. Suppression of sharp waves and ripples in sleep or during immobility can interfere with memories expressed at

18758-404: The hippocampus is dysfunctional, orientation is affected; people may have difficulty in remembering how they arrived at a location and how to proceed further. Getting lost is a common symptom of amnesia. Studies with animals have shown that an intact hippocampus is required for initial learning and long-term retention of some spatial memory tasks, in particular ones that require finding the way to

18924-432: The hippocampus more than of other parts of the brain. These effects show up in post-traumatic stress disorder , and they may contribute to the hippocampal atrophy reported in schizophrenia and severe depression . Anterior hippocampal volume in children is positively correlated with parental family income and this correlation is thought to be mediated by income related stress. A recent study has also revealed atrophy as

19090-542: The hippocampus of elderly people , but later studies using more precise techniques found only minimal differences. Similarly, some MRI studies have reported shrinkage of the hippocampus in elderly people, but other studies have failed to reproduce this finding. There is, however, a reliable relationship between the size of the hippocampus and memory performance; so that where there is age-related shrinkage, memory performance will be impaired. There are also reports that memory tasks tend to produce less hippocampal activation in

19256-530: The hippocampus to space. The spatial theory was originally championed by O'Keefe and Nadel, who were influenced by American psychologist E.C. Tolman's theories about " cognitive maps " in humans and animals. O'Keefe and his student Dostrovsky in 1971 discovered neurons in the rat hippocampus that appeared to them to show activity related to the rat's location within its environment. Despite skepticism from other investigators, O'Keefe and his co-workers, especially Lynn Nadel, continued to investigate this question, in

19422-453: The hippocampus was reactivated, memory traces consolidated by non-hippocampal systems were not recalled, suggesting that the hippocampus interferes with long-term memory consolidation in other memory-related systems. One of the major implications that this model illustrates is the dominant effects of the hippocampus on non-hippocampal networks when information is incongruent. With this information in mind, future directions could lead towards

19588-485: The hippocampus was unchanged, as the increase seen in the posterior part was made at the expense of the anterior part, which showed a relative decrease in size. There have been no reported adverse effects from this disparity in hippocampal proportions. Another study showed opposite findings in blind individuals. The anterior part of the right hippocampus was larger and the posterior part was smaller, compared with sighted individuals. There are several navigational cells in

19754-442: The hippocampus. The parietal cortex encodes spatial information using an egocentric frame of reference. It is therefore involved in the transformation of sensory information coordinates into action or effector coordinates by updating the spatial representation of the body within the environment. As a result, lesions to the parietal cortex produce deficits in the acquisition and retention of egocentric tasks, whereas minor impairment

19920-421: The house the cat went to was the owner's old house. The owners and the cat had not lived in that house for well over a year. Logie (1995) proposed that the visuo-spatial sketchpad is broken down into two subcomponents, one visual and one spatial. These are the visual cache and the inner scribe, respectively. The visual cache is a temporary visual store including such dimensions as color and shape. Conversely,

20086-448: The inner scribe is a rehearsal mechanism for visual information and is responsible for information concerning movement sequences. Although a general lack of consensus regarding this distinction has been noted in the literature, there is a growing amount of evidence that the two components are separate and serve different functions. Visual memory is responsible for retaining visual shapes and colors (i.e., what), whereas spatial memory

20252-482: The issue further. People perceive objects in their environment relative to other objects in that same environment. Landmarks and layout are complementary systems for spatial recall, but it is unknown how these two systems interact when both types of information are available. As a result, people have to make certain assumptions about the interaction between the two systems. For example, cognitive maps are not "absolute" but rather, as anyone can attest, are "used to provide

20418-433: The left posterior, left anterior or right anterior hippocampus demonstrate distinct, individual cell responses when presented with faces of presumably recognizable famous people. Associations among facial and vocal identity were similarly mapped to the hippocampus of rheseus monkeys. Single neurons in the CA1 and CA3 responded strongly to social stimulus recognition by MRI. The CA2 was not distinguished, and may likely comprise

20584-402: The level of the behavior, nonetheless, the newly formed CA1 place cell code can re-emerge even after a sleep with abolished sharp waves and ripples, in spatially non-demanding tasks. Since at least the time of Ramon y Cajal (1852–1934), psychologists have speculated that the brain stores memory by altering the strength of connections between neurons that are simultaneously active. This idea

20750-451: The limitations of both visuo-spatial STM and WM. Certain species of paridae and corvidae (such as the black-capped chickadee and the scrub jay ) are able to use spatial memory to remember where, when and what type of food they have cached. Studies on rats and squirrels have also suggested that they are able to use spatial memory to locate previously hidden food. Experiments using the radial maze have allowed researchers to control for

20916-497: The literature, it is suggested that further research into the fractionation of STM and WM be explored. However, much of the research into the visuo-spatial memory construct have been conducted in accordance to the paradigm advanced by Baddeley and Hitch. Research into the exact function of the visuo-spatial sketchpad has indicated that both spatial short-term memory and working memory are dependent on executive resources and are not entirely distinct. For instance, performance on

21082-501: The luxury of extreme control over their test environment. Any variable can be manipulated, including things that would not be possible in reality. During a 2006 study, researchers designed three different virtual towns, each of which had its own "unique road layout and a unique set of five stores." However, the overall footprint of the different maps was exactly the same size, 80 sq. units. In this experiment, participants had to partake in two different sets of trials. A study conducted at

21248-554: The main olfactory bulb, the anterior olfactory nucleus, and to the primary olfactory cortex. There continues to be some interest in hippocampal olfactory responses, in particular, the role of the hippocampus in memory for odors, but few specialists today believe that olfaction is its primary function. Over the years, three main ideas of hippocampal function have dominated the literature: response inhibition , episodic memory , and spatial cognition. The behavioral inhibition theory (caricatured by John O'Keefe and Lynn Nadel as "slam on

21414-455: The maze. Spatial learning In cognitive psychology and neuroscience , spatial memory is a form of memory responsible for the recording and recovery of information needed to plan a course to a location and to recall the location of an object or the occurrence of an event. Spatial memory is necessary for orientation in space. Spatial memory can also be divided into egocentric and allocentric spatial memory. A person's spatial memory

21580-460: The medial septum is more than just the controller of theta; it is also the main source of cholinergic projections to the hippocampus. It has not been established that septal lesions exert their effects specifically by eliminating the theta rhythm. During sleep or during resting, when an animal is not engaged with its surroundings, the hippocampal EEG shows a pattern of irregular slow waves, somewhat larger in amplitude than theta waves. This pattern

21746-490: The moderate projections to two primary olfactory cortical areas and prelimbic areas of the medial prefrontal cortex . This region has the smallest number of place cells. The ventral hippocampus functions in fear conditioning and affective processes. Anagnostaras et al. (2002) showed that alterations to the ventral hippocampus reduced the amount of information sent to the amygdala by the dorsal and ventral hippocampus, consequently altering fear conditioning in rats. Historically,

21912-542: The most active of them. An active cell typically stays active for half a second to a few seconds. As the rat behaves, the active cells fall silent and new cells become active, but the overall percentage of active cells remains more or less constant. In many situations, cell activity is determined largely by the spatial location of the animal, but other behavioral variables also clearly influence it. The LIA mode appears during slow-wave (non-dreaming) sleep, and also during states of waking immobility such as resting or eating. In

22078-440: The most intensively studied subject in medical history. In the ensuing years, other patients with similar levels of hippocampal damage and amnesia (caused by accident or disease) have also been studied, and thousands of experiments have studied the physiology of activity-driven changes in synaptic connections in the hippocampus. There is now universal agreement that the hippocampi play some sort of important role in memory; however,

22244-460: The neighboring entorhinal cortex . The earliest description of the ridge running along the floor of the temporal horn of the lateral ventricle comes from the Venetian anatomist Julius Caesar Aranzi (1587), who likened it first to a silkworm and then to a seahorse ( Latin hippocampus , from Greek ἱππόκαμπος, from ἵππος, 'horse' + κάμπος, 'sea monster'). The German anatomist Duvernoy (1729),

22410-448: The numerical test items with spatial ones. On average, most participants achieve a span of five items on the Corsi span test and seven on the digit span task. The visual pattern span is similar to the Corsi block tapping test but regarded as a more pure test of visual short-term recall. Participants are presented with a series of matrix patterns that have half their cells colored and the other half blank. The matrix patterns are arranged in

22576-457: The orientation of the observer." People use both the layout of a particular space and the presence of orienting landmarks in order to navigate. Psychologists have yet to explain whether layout affects landmarks or if landmarks determine the boundaries of a layout. Because of this, the concept suffers from a chicken and the egg paradox. McNamara has found that subjects use "clusters of landmarks as intrinsic frames of reference," which only confuses

22742-410: The outer in – the molecular layer , the inner molecular layer , the granular layer , and the hilus . The CA3 in the hippocampus proper has the following cell layers known as strata: lacunosum-moleculare, radiatum, lucidum, pyramidal, and oriens. CA2 and CA1 also have these layers except the lucidum stratum . The input to the hippocampus (from varying cortical and subcortical structures) comes from

22908-422: The output to the EC, additional output pathways go to other cortical areas including the prefrontal cortex . A major output goes via the fornix to the lateral septal area and to the mammillary body of the hypothalamus (which the fornix interconnects with the hippocampus). The hippocampus receives modulatory input from the serotonin , norepinephrine , and dopamine systems, and from the nucleus reuniens of

23074-401: The paths in between tests). In the T-maze this is relegated to a single left or right turn, but in more complex mazes it becomes a series of turns for the rat to remember in order to reach its goal and reward. A poorly working spatial memory can result in a rat getting repeatedly lost in the maze regardless of how successful previous attempts were or how unchanged the maze is. The hippocampus

23240-410: The pathway varies depending on the level of difficulty (1-10) and the matrices themselves may vary in length from 2 x 2 cells to 6 x 6. Dynamic mazes are intended for measuring spatial ability in children. With this test, an experimenter presents the participant with a drawing of a maze with a picture of a man in the center. While the participant watches, the experimenter uses his or her finger to trace

23406-444: The phase with which theta rhythms, at the time of stimulation of a neuron, shape the effect of that stimulation upon its synapses. What is meant here is that theta rhythms may affect those aspects of learning and memory that are dependent upon synaptic plasticity . It is well established that lesions of the medial septum  – the central node of the theta system – cause severe disruptions of memory. However,

23572-430: The point of near convergence. In an attempt to reconcile the two disparate views, it is suggested that a broader view of the hippocampal function is taken and seen to have a role that encompasses both the organisation of experience ( mental mapping , as per Tolman's original concept in 1948) and the directional behaviour seen as being involved in all areas of cognition, so that the function of the hippocampus can be viewed as

23738-517: The precise nature of this role remains widely debated. A recent theory proposed – without questioning its role in spatial cognition – that the hippocampus encodes new episodic memories by associating representations in the newborn granule cells of the dentate gyrus and arranging those representations sequentially in the CA3 by relying on the phase precession generated in the entorhinal cortex . The third important theory of hippocampal function relates

23904-408: The pyramidal cells and then give an inhibitory feedback to the pyramidal cells. This recurrent inhibition is a simple feedback circuit that can dampen excitatory responses in the hippocampus. The pyramidal cells give a recurrent excitation which is an important mechanism found in some memory processing microcircuits. Several other connections play important roles in hippocampal function. Beyond

24070-405: The rat can be a cause of a natural preference within the rat. A study of alternation can be performed by repeating the experiment multiple times with no reward in either arm of the maze. Another experiment that can be performed is the alternation of rewards each time the experiment is performed, proving the rat will choose the arm that was not visited each time the experiment starts. Rewards within

24236-416: The rat is responsible for recording information about the rat's environment as well as its spatial orientation. It is this spatial memory that allows the rat to navigate its way through the various types of mazes and challenges presented to it by the experimenters. This also allows the rat to navigate the same maze multiple times while remembering the correct and incorrect pathways (unless the scientists change

24402-445: The rat's psyche on multiple subjects, and ultimately divulge further into the rat's psychological characteristics. It is also important to consider the rodent's behavior. The use of spatial and non-spatial cues is very influential to research findings on memory, spatial learning and the long-term potentiation (LTP). These cues include the orientation of the maze, extra-maze cues and room configuration cues. Strategies may be affected by

24568-429: The rats can be types of food, another rat within a cage, an odor, or a type of shelter. By performing this type of experiment, the rat's preferences can be determined. Examples of this could be a rat's food preferences, its familiarity with specific smells and scents, the attraction of the male and female within the maze, and whether a young rat prefers an adult female or an adult male. These simple experiments can determine

24734-607: The results of surgical destruction of the hippocampi when trying to relieve epileptic seizures in an American man Henry Molaison , known until his death in 2008 as "Patient H.M." The unexpected outcome of the surgery was severe anterograde and partial retrograde amnesia ; Molaison was unable to form new episodic memories after his surgery and could not remember any events that occurred just before his surgery, but he did retain memories of events that occurred many years earlier extending back into his childhood. This case attracted such widespread professional interest that Molaison became

24900-399: The rodent's ability to find cues in the room, the presence or absence of polarizing cues in the room, and the stability of the maze in the room. When analyzing and interpreting experimental data, researchers have to consider the orientation and configuration of the apparatus and cues in the room. This type of apparatus includes multiple T-mazes connected which result in a very complex maze. It

25066-465: The same time. Drugs that interfere with NMDA receptors block LTP and have major effects on some types of memory, especially spatial memory. Genetically modified mice that are modified to disable the LTP mechanism, also generally show severe memory deficits. Age-related conditions such as Alzheimer's disease and other forms of dementia (for which hippocampal disruption is one of the earliest signs ) have

25232-412: The set of structures that line the deep edge of the cortex (Latin limbus meaning border ): These include the hippocampus, cingulate cortex , olfactory cortex , and amygdala . Paul MacLean later suggested that the limbic structures comprise the neural basis of emotion. The hippocampus is anatomically connected to parts of the brain that are involved with emotional behavior – the septum ,

25398-424: The source of their seizures , with a view to surgical resection. The patients had diagnostic electrodes implanted in their hippocampus and then used a computer to move around in a virtual reality town. Similar brain imaging studies in navigation have shown the hippocampus to be active. A study was carried out on taxi drivers. London's black cab drivers need to learn the locations of a large number of places and

25564-476: The spiking of hippocampal neurons and synchronise across the hippocampus in a travelling wave pattern. The trisynaptic circuit is a relay of neurotransmission in the hippocampus that interacts with many brain regions. From rodent studies it has been proposed that the trisynaptic circuit generates the hippocampal theta rhythm. Theta rhythmicity is very obvious in rabbits and rodents and also clearly present in cats and dogs. Whether theta can be seen in primates

25730-445: The study of these non-hippocampal memory systems through hippocampal inactivation, further expanding the labile constructs of memory. Additionally, many theories of memory are holistically based around the hippocampus. This model could add beneficial information to hippocampal research and memory theories such as the multiple trace theory . Lastly, the between-system memory interference model allows researchers to evaluate their results on

25896-426: The taxi drivers' (experts') recall of streets was higher in both the route order condition and the map order condition than in the two random conditions. This indicates that the experts were able to use their prelearned spatial knowledge to organize the information in such a way that they surpassed STM and WM capacity limitations. The organization strategy that the drivers employed is known as chunking . Additionally,

26062-417: The test is named. The subject is placed in a round tank of translucent water with walls that are too high for it to climb out and water that is too deep for it to stand in. The walls of the tank are decorated with visual cues to serve as reference points. The rat must swim around the pool until by chance it discovers just below the surface the hidden platform onto which it can climb. Typically, rats swim around

26228-401: The theta mode, the EEG is dominated by large regular waves with a frequency range of 6 to 9 Hz , and the main groups of hippocampal neurons ( pyramidal cells and granule cells ) show sparse population activity, which means that in any short time interval, the great majority of cells are silent, while the small remaining fraction fire at relatively high rates, up to 50 spikes in one second for

26394-426: The theta wave are generated mainly by densely packed neural layers of the entorhinal cortex, CA3, and the dendrites of pyramidal cells. The theta wave is one of the largest signals seen on EEG, and is known as the hippocampal theta rhythm . In some situations the EEG is dominated by regular waves at 3 to 10 Hz, often continuing for many seconds. These reflect subthreshold membrane potentials and strongly modulate

26560-499: The transfer of memories out of the hippocampus to other parts of the brain. Experiments using intrahippocampal transplantation of hippocampal cells in primates with neurotoxic lesions of the hippocampus have shown that the hippocampus is required for the formation and recall, but not the storage, of memories. It has been shown that a decrease in the volume of various parts of the hippocampus in people leads to specific memory impairments. In particular, efficiency of verbal memory retention

26726-446: The unique abilities involved in either visual or spatial memory. For example, the visual patterns test (VPT) measures visual span whereas the Corsi Blocks Task measures spatial span. Correlational studies of the two measures suggest a separation between visual and spatial abilities, due to a lack of correlation found between them in both healthy and brain damaged patients. Support for the division of visual and spatial memory components

26892-442: The visuo-spatial sketchpad, is likely responsible for the temporary storage, maintenance, and manipulation of both visual and spatial information. In contrast to the multi-component model, some researchers believe that STM should be viewed as a unitary construct. In this respect, visual, spatial, and verbal information are thought to be organized by levels of representation rather than the type of store to which they belong. Within

27058-414: The world's layout. McNamara, Hardy and Hirtle identified region membership as a major building block of anyone's cognitive map (1989). Specifically, region membership is defined by any kind of boundary, whether physical, perceptual or subjective (McNamara et al., 1989). Boundaries are among the most basic and endemic qualities in the world around us. These boundaries are nothing more than axial lines which are

27224-402: Was formalized by Donald Hebb in 1949, but for many years remained unexplained. In 1973, Tim Bliss and Terje Lømo described a phenomenon in the rabbit hippocampus that appeared to meet Hebb's specifications: a change in synaptic responsiveness induced by brief strong activation and lasting for hours or days or longer. This phenomenon was soon referred to as long-term potentiation (LTP). As

27390-508: Was labeled by Chun and Jiang in 1998. Landmarks give people guidance by activating "learned associations between the global context and target locations." Mallot and Gillner (2000) showed that subjects learned an association between a specific landmark and the direction of a turn, thereby furthering the relationship between associations and landmarks. Shelton and McNamara (2001) succinctly summed up why landmarks, as markers, are so helpful: "location...cannot be described without making reference to

27556-461: Was suggested that the mechanisms of memory and planning both evolved from mechanisms of navigation and that their neuronal algorithms were basically the same. Many studies have made use of neuroimaging techniques such as functional magnetic resonance imaging (fMRI), and a functional role in approach-avoidance conflict has been noted. The anterior hippocampus is seen to be involved in decision-making under approach-avoidance conflict processing. It

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