The P300 ( P3 ) wave is an event-related potential (ERP) component elicited in the process of decision making. It is considered to be an endogenous potential, as its occurrence links not to the physical attributes of a stimulus, but to a person's reaction to it. More specifically, the P300 is thought to reflect processes involved in stimulus evaluation or categorization.
100-401: P300 may mean: P300 (neuroscience) , a neural evoked potential component of the electroencephalogram (EEG) p300 (or EP300 ), a transcriptional coactivator Nikon P300 , a mid-class compact digital camera, produced by Nikon in 2011 [REDACTED] Topics referred to by the same term This disambiguation page lists articles associated with
200-409: A click or a flash. They found that when subjects were required to guess what the following stimulus would be, the amplitude of the "late positive complex" was larger than when they knew what the stimulus would be. In a second experiment, they presented two cue types. For one cue there was a 2 in 3 chance that the following stimulus would be a click and a 1 in 3 chance that the following stimulus would be
300-458: A common ancestor that appeared late in the Cryogenian period, 700–650 million years ago, and it has been hypothesized that this common ancestor had the shape of a simple tubeworm with a segmented body. At a schematic level, that basic worm-shape continues to be reflected in the body and nervous system architecture of all modern bilaterians, including vertebrates. The fundamental bilateral body form
400-407: A flash. The second cue type had probabilities that were the reverse of the first. They found that the amplitude of the positive complex was larger in response to the less probable stimuli, or the one that only had a 1 in 3 chance of appearing. Another important finding from these studies is that this late positive complex was observed for both the clicks and flashes, indicating that the physical type of
500-460: A foundation for the extensive work on the P300 in the decades that followed. The P3a, or novelty P3, has a positive-going amplitude that displays maximum amplitude over frontal/central electrode sites and has a peak latency in the range of 250–280 ms. The P3a has been associated with brain activity related to the engagement of attention (especially the orienting , involuntary shifts to changes in
600-471: A gradient of size and complexity that roughly follows the evolutionary sequence. All of these brains contain the same set of basic anatomical structures, but many are rudimentary in the hagfish, whereas in mammals the foremost part ( forebrain , especially the telencephalon ) is greatly developed and expanded. Brains are most commonly compared in terms of their mass . The relationship between brain size , body size and other variables has been studied across
700-569: A lighter color. Further information can be gained by staining slices of brain tissue with a variety of chemicals that bring out areas where specific types of molecules are present in high concentrations. It is also possible to examine the microstructure of brain tissue using a microscope, and to trace the pattern of connections from one brain area to another. The brains of all species are composed primarily of two broad classes of brain cells : neurons and glial cells . Glial cells (also known as glia or neuroglia ) come in several types, and perform
800-443: A much larger proportion of the brain for primates than for other species, and an especially large fraction of the human brain. The brain develops in an intricately orchestrated sequence of stages. It changes in shape from a simple swelling at the front of the nerve cord in the earliest embryonic stages, to a complex array of areas and connections. Neurons are created in special zones that contain stem cells , and then migrate through
900-491: A neuron is in place, it extends dendrites and an axon into the area around it. Axons, because they commonly extend a great distance from the cell body and need to reach specific targets, grow in a particularly complex way. The tip of a growing axon consists of a blob of protoplasm called a growth cone , studded with chemical receptors. These receptors sense the local environment, causing the growth cone to be attracted or repelled by various cellular elements, and thus to be pulled in
1000-470: A number of critical functions, including structural support, metabolic support, insulation, and guidance of development. Neurons, however, are usually considered the most important cells in the brain. In humans, the cerebral cortex contains approximately 14–16 billion neurons, and the estimated number of neurons in the cerebellum is 55–70 billion. Each neuron is connected by synapses to several thousand other neurons. The property that makes neurons unique
1100-455: A particular direction at each point along its path. The result of this pathfinding process is that the growth cone navigates through the brain until it reaches its destination area, where other chemical cues cause it to begin generating synapses. Considering the entire brain, thousands of genes create products that influence axonal pathfinding. The synaptic network that finally emerges is only partly determined by genes, though. In many parts of
SECTION 10
#17328513219951200-512: A previously existing brain structure. This category includes tardigrades , arthropods , molluscs , and numerous types of worms. The diversity of invertebrate body plans is matched by an equal diversity in brain structures. Two groups of invertebrates have notably complex brains: arthropods (insects, crustaceans , arachnids , and others), and cephalopods (octopuses, squids , and similar molluscs). The brains of arthropods and cephalopods arise from twin parallel nerve cords that extend through
1300-485: A prominent tool used to study cognitive processes, especially psychology research on information processing. Generally speaking, improbable events will elicit a P3b, and the less probable the event, the larger the P3b amplitude. This was shown to be true both for the overall probability and for the local probability. However, in order to elicit a P3b, the improbable event must be related to the task at hand in some way (for example,
1400-454: A time in a sequence. For every two numbers, the subjects were required to make simple decisions, such as telling which of the two numbers was numerically smaller or larger, which came first or second in the sequence, or whether they were equal. When examining evoked potentials to these stimuli (i.e., ERPs), Chapman and Bragdon found that both the numbers and the flashes elicited the expected sensory responses (e.g., visual N1 components), and that
1500-486: A way that reflects in part the complexity of their behavior. For example, primates have brains 5 to 10 times larger than the formula predicts. Predators , who have to implement various hunting strategies against the ever changing anti-predator adaptations , tend to have larger brains relative to body size than their prey. All vertebrate brains share a common underlying form, which appears most clearly during early stages of embryonic development . In its earliest form,
1600-483: A wide range of vertebrate species. As a rule of thumb , brain size increases with body size, but not in a simple linear proportion. In general, smaller animals tend to have proportionally larger brains, measured as a fraction of body size. For mammals, the relationship between brain volume and body mass essentially follows a power law with an exponent of about 0.75. This formula describes the central tendency, but every family of mammals departs from it to some degree, in
1700-412: A wide variety of biochemical and metabolic processes, most notably the interactions between neurotransmitters and receptors that take place at synapses. Neurotransmitters are chemicals that are released at synapses when the local membrane is depolarised and Ca enters into the cell, typically when an action potential arrives at the synapse – neurotransmitters attach themselves to receptor molecules on
1800-405: Is a list of some of the most important vertebrate brain components, along with a brief description of their functions as currently understood: Modern reptiles and mammals diverged from a common ancestor around 320 million years ago. The number of extant reptiles far exceeds the number of mammalian species, with 11,733 recognized species of reptiles compared to 5,884 extant mammals. Along with
1900-436: Is a tube with a hollow gut cavity running from the mouth to the anus, and a nerve cord with an enlargement (a ganglion ) for each body segment, with an especially large ganglion at the front, called the brain. The brain is small and simple in some species, such as nematode worms; in other species, such as vertebrates, it is a large and very complex organ. Some types of worms, such as leeches , also have an enlarged ganglion at
2000-460: Is almost always inhibitory. Neurons using these transmitters can be found in nearly every part of the brain. Because of their ubiquity, drugs that act on glutamate or GABA tend to have broad and powerful effects. Some general anesthetics act by reducing the effects of glutamate; most tranquilizers exert their sedative effects by enhancing the effects of GABA. There are dozens of other chemical neurotransmitters that are used in more limited areas of
2100-487: Is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals . It consists of nervous tissue and is typically located in the head ( cephalization ), usually near organs for special senses such as vision , hearing and olfaction . Being the most specialized organ, it is responsible for receiving information from the sensory nervous system , processing those information ( thought , cognition , and intelligence ) and
SECTION 20
#17328513219952200-412: Is by visual inspection, but many more sophisticated techniques have been developed. Brain tissue in its natural state is too soft to work with, but it can be hardened by immersion in alcohol or other fixatives , and then sliced apart for examination of the interior. Visually, the interior of the brain consists of areas of so-called grey matter , with a dark color, separated by areas of white matter , with
2300-403: Is consistently detectable and is elicited in response to precise stimuli. The P300 waveform can also be evoked in nearly all subjects with little variation in measurement techniques, which may help simplify interface designs and permit greater usability. The speed at which an interface is able to operate depends on how detectable the signal is despite "noise." One negative characteristic of the P300
2400-582: Is critical at key periods of development. Additionally, the quantity and quality of experience are important. For example, animals raised in enriched environments demonstrate thick cerebral cortices, indicating a high density of synaptic connections, compared to animals with restricted levels of stimulation. The functions of the brain depend on the ability of neurons to transmit electrochemical signals to other cells, and their ability to respond appropriately to electrochemical signals received from other cells. The electrical properties of neurons are controlled by
2500-450: Is involved in the sense of smell, and the dentate gyrus of the hippocampus, where there is evidence that the new neurons play a role in storing newly acquired memories. With these exceptions, however, the set of neurons that is present in early childhood is the set that is present for life. Glial cells are different: as with most types of cells in the body, they are generated throughout the lifespan. There has long been debate about whether
2600-432: Is related to control of movements, neurotransmitters and neuromodulators responsible for integrating inputs and transmitting outputs are present, sensory systems, and cognitive functions. The avian brain is the central organ of the nervous system in birds. Birds possess large, complex brains, which process , integrate , and coordinate information received from the environment and make decisions on how to respond with
2700-491: Is responsible for the cognitive functions of birds. The pallium is made up of several major structures: the hyperpallium, a dorsal bulge of the pallium found only in birds, as well as the nidopallium, mesopallium, and archipallium. The bird telencephalon nuclear structure, wherein neurons are distributed in three-dimensionally arranged clusters, with no large-scale separation of white matter and grey matter , though there exist layer-like and column-like connections. Structures in
2800-409: Is that the amplitude of the waveform requires averaging of multiple recordings to isolate the signal. This and other post-recording processing steps determine the overall speed of an interface. The algorithm proposed by Farwell and Donchin provides an example of a simple BCI that relies on the unconscious decision making processes of the P300 to drive a computer. A 6×6 grid of characters is presented to
2900-496: Is the brain's primary mechanism for learning and memory. Most of the space in the brain is taken up by axons, which are often bundled together in what are called nerve fiber tracts . A myelinated axon is wrapped in a fatty insulating sheath of myelin , which serves to greatly increase the speed of signal propagation. (There are also unmyelinated axons). Myelin is white, making parts of the brain filled exclusively with nerve fibers appear as light-colored white matter , in contrast to
3000-438: Is their ability to send signals to specific target cells, sometimes over long distances. They send these signals by means of an axon , which is a thin protoplasmic fiber that extends from the cell body and projects, usually with numerous branches, to other areas, sometimes nearby, sometimes in distant parts of the brain or body. The length of an axon can be extraordinary: for example, if a pyramidal cell (an excitatory neuron) of
3100-400: Is used to compare brain sizes across species. It takes into account the nonlinearity of the brain-to-body relationship. Humans have an average EQ in the 7-to-8 range, while most other primates have an EQ in the 2-to-3 range. Dolphins have values higher than those of primates other than humans, but nearly all other mammals have EQ values that are substantially lower. Most of the enlargement of
P300 - Misplaced Pages Continue
3200-399: Is usually elicited using the oddball paradigm , in which low-probability target items are mixed with high-probability non-target (or "standard") items. When recorded by electroencephalography (EEG), it surfaces as a positive deflection in voltage with a latency (delay between stimulus and response) of roughly 250 to 500 ms. In the scientific literature a differentiation is often made in
3300-439: Is yet to be solved. Recent models in modern neuroscience treat the brain as a biological computer , very different in mechanism from a digital computer , but similar in the sense that it acquires information from the surrounding world, stores it, and processes it in a variety of ways. This article compares the properties of brains across the entire range of animal species, with the greatest attention to vertebrates. It deals with
3400-466: The Cambrian period , and may have resembled the modern jawless fish ( hagfish and lamprey ) in form. Jawed vertebrates appeared by 445 Mya, tetrapods by 350 Mya, amniotes by 310 Mya and mammaliaforms by 200 Mya (approximately). Each vertebrate clade has an equally long evolutionary history, but the brains of modern fish , amphibians , reptiles , birds and mammals show
3500-456: The cerebral cortex and the cerebellar cortex, are folded into convoluted gyri and sulci in order to maximize surface area within the available intracranial space . Other parts, such as the thalamus and hypothalamus, consist of many small clusters of nuclei known as "ganglia". Thousands of distinguishable areas can be identified within the vertebrate brain based on fine distinctions of neural structure, chemistry, and connectivity. Although
3600-448: The diencephalon (which will contain the thalamus and hypothalamus). At about the same time, the hindbrain splits into the metencephalon (which will contain the cerebellum and pons) and the myelencephalon (which will contain the medulla oblongata ). Each of these areas contains proliferative zones where neurons and glial cells are generated; the resulting cells then migrate, sometimes for long distances, to their final positions. Once
3700-423: The environment . Some basic types of responsiveness such as reflexes can be mediated by the spinal cord or peripheral ganglia , but sophisticated purposeful control of behavior based on complex sensory input requires the information integrating capabilities of a centralized brain. The operations of individual brain cells are now understood in considerable detail but the way they cooperate in ensembles of millions
3800-399: The forebrain (prosencephalon, subdivided into telencephalon and diencephalon ), midbrain ( mesencephalon ) and hindbrain ( rhombencephalon , subdivided into metencephalon and myelencephalon ). The spinal cord , which directly interacts with somatic functions below the head, can be considered a caudal extension of the myelencephalon enclosed inside the vertebral column . Together,
3900-441: The human brain insofar as it shares the properties of other brains. The ways in which the human brain differs from other brains are covered in the human brain article. Several topics that might be covered here are instead covered there because much more can be said about them in a human context. The most important that are covered in the human brain article are brain disease and the effects of brain damage . The shape and size of
4000-450: The neural tube , a hollow cord of cells with a fluid-filled ventricle at the center. At the front end, the ventricles and cord swell to form three vesicles that are the precursors of the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain). At the next stage, the forebrain splits into two vesicles called the telencephalon (which will contain the cerebral cortex, basal ganglia, and related structures) and
4100-423: The skull from the brain. Cerebral arteries pierce the outer two layers of the meninges, the dura and arachnoid mater , into the subarachnoid space and perfuse the brain parenchyma via arterioles perforating into the innermost layer of the meninges, the pia mater . The endothelial cells in the cerebral blood vessel walls are joined tightly to one another, forming the blood–brain barrier , which blocks
P300 - Misplaced Pages Continue
4200-556: The EEG. The speed of the highlighting determines the number of characters processed per minute. Results from studies using this setup show that normal subjects could achieve a 95% success rate at 3.4–4.3 chars/min. Such success rates are not limited to non-disabled users; a study conducted in 2000 revealed that 4 paralyzed participants (one with complete paraplegia, three with incomplete paraplegia) performed as successfully as 10 normal participants. Scientific research often relies on measurement of
4300-459: The P3, which is divided according to time: Early P3 window (300-400 ms) and Late P3 window (380-440 ms). The signal is typically measured most strongly by the electrodes covering the parietal lobe . The presence, magnitude, topography and timing of this signal are often used as metrics of cognitive function in decision-making processes. While the neural substrates of this ERP component still remain hazy,
4400-520: The P300 to examine event related potentials, especially with regard to decision making. Because cognitive impairment is often correlated with modifications in the P300, the waveform can be used as a measure for the efficacy of various treatments on cognitive function. Some have suggested its use as a clinical marker for precisely these reasons. There is a broad range of uses for the P300 in clinical research. Some research groups have performed fMRI combined to EEG in order to achieve inner-speech dictation and
4500-411: The P300. The technique relies on reproducible elicitation of the P300 wave, central to the idea of a Memory and Encoding Related Multifaceted Electroencephalographic Response (MERMER) developed by Dr. Lawrence Farwell . Applications in brain-computer interfacing (BCI) have also been proposed. The P300 has a number of desirable qualities that aid in implementation of such systems. First, the waveform
4600-455: The amplitude of these responses varied in an expected fashion with the intensity of the stimuli. They also found that the ERP responses to the numbers, but not to the light flashes, contained a large positivity that peaked around 300 ms after the stimulus appeared. Chapman and Bragdon speculated that this differential response to the numbers, which came to be known as the P300 response, resulted from
4700-402: The animal is actively engaged in a task, called beta and gamma waves . During an epileptic seizure , the brain's inhibitory control mechanisms fail to function and electrical activity rises to pathological levels, producing EEG traces that show large wave and spike patterns not seen in a healthy brain. Relating these population-level patterns to the computational functions of individual neurons
4800-477: The animal. The tegmentum receives incoming sensory information and forwards motor responses to and from the forebrain. The isthmus connects the hindbrain with midbrain. The forebrain region is particularly well developed, is further divided into diencephalon and telencephalon. Diencephalon is related to regulation of eye and body movement in response to visual stimuli, sensory information, circadian rhythms , olfactory input, and autonomic nervous system .Telencephalon
4900-452: The approach of inner-speech recognition. The P300 wave obtained by visual stimulation is used to assess cognitive processes in humans, and the value of the latency and amplitude of the P300 wave can be a measure of the severity of dementia processes. The analysis of P300 wave latency seems to be particularly useful in the diagnosis of mild cognitive impairment (MCI). Brain The brain
5000-403: The back end of the nerve cord, known as a "tail brain". There are a few types of existing bilaterians that lack a recognizable brain, including echinoderms and tunicates . It has not been definitively established whether the existence of these brainless species indicates that the earliest bilaterians lacked a brain, or whether their ancestors evolved in a way that led to the disappearance of
5100-508: The body of the animal. Arthropods have a central brain, the supraesophageal ganglion , with three divisions and large optical lobes behind each eye for visual processing. Cephalopods such as the octopus and squid have the largest brains of any invertebrates. There are several invertebrate species whose brains have been studied intensively because they have properties that make them convenient for experimental work: The first vertebrates appeared over 500 million years ago ( Mya ) during
SECTION 50
#17328513219955200-416: The body. Neuroanatomists usually divide the vertebrate brain into six main subregions: the telencephalon (the cerebral hemispheres ), diencephalon ( thalamus and hypothalamus ), mesencephalon (midbrain), cerebellum , pons and medulla oblongata , with the midbrain, pons and medulla often collectively called the brainstem . Each of these areas has a complex internal structure. Some parts, such as
5300-588: The brain and spinal cord constitute the central nervous system in all vertebrates. In humans , the cerebral cortex contains approximately 14–16 billion neurons, and the estimated number of neurons in the cerebellum is 55–70 billion. Each neuron is connected by synapses to several thousand other neurons, typically communicating with one another via cytoplasmic processes known as dendrites and axons . Axons are usually myelinated and carry trains of rapid micro-electric signal pulses called action potentials to target specific recipient cells in other areas of
5400-498: The brain appears as three vesicular swellings at the front end of the neural tube ; these swellings eventually become the forebrain ( prosencephalon ), midbrain ( mesencephalon ) and hindbrain ( rhombencephalon ), respectively. At the earliest stages of brain development, the three areas are roughly equal in size. In many aquatic / semiaquatic vertebrates such as fish and amphibians, the three parts remain similar in size in adults , but in terrestrial tetrapods such as mammals,
5500-509: The brain but are not as ubiquitously distributed as glutamate and GABA. As a side effect of the electrochemical processes used by neurons for signaling, brain tissue generates electric fields when it is active. When large numbers of neurons show synchronized activity, the electric fields that they generate can be large enough to detect outside the skull, using electroencephalography (EEG) or magnetoencephalography (MEG). EEG recordings, along with recordings made from electrodes implanted inside
5600-401: The brain in reptiles and mammals, with shared neuronal clusters enlightening brain evolution. Conserved transcription factors elucidate that evolution acted in different areas of the brain by either retaining similar morphology and function, or diversifying it. Anatomically, the reptilian brain has less subdivisions than the mammalian brain, however it has numerous conserved aspects including
5700-445: The brain or distant parts of the body. The prefrontal cortex , which controls executive functions , is particularly well developed in humans. Physiologically , brains exert centralized control over a body's other organs. They act on the rest of the body both by generating patterns of muscle activity and by driving the secretion of chemicals called hormones . This centralized control allows rapid and coordinated responses to changes in
5800-511: The brain to the spinal cord. The most obvious difference between the brains of mammals and other vertebrates is their size. On average, a mammal has a brain roughly twice as large as that of a bird of the same body size, and ten times as large as that of a reptile of the same body size. Size, however, is not the only difference: there are also substantial differences in shape. The hindbrain and midbrain of mammals are generally similar to those of other vertebrates, but dramatic differences appear in
5900-467: The brain varies greatly between species, and identifying common features is often difficult. Nevertheless, there are a number of principles of brain architecture that apply across a wide range of species. Some aspects of brain structure are common to almost the entire range of animal species; others distinguish "advanced" brains from more primitive ones, or distinguish vertebrates from invertebrates. The simplest way to gain information about brain anatomy
6000-402: The brain, axons initially "overgrow", and then are "pruned" by mechanisms that depend on neural activity. In the projection from the eye to the midbrain, for example, the structure in the adult contains a very precise mapping, connecting each point on the surface of the retina to a corresponding point in a midbrain layer. In the first stages of development, each axon from the retina is guided to
6100-439: The brain, often areas dedicated to a particular function. Serotonin , for example—the primary target of many antidepressant drugs and many dietary aids—comes exclusively from a small brainstem area called the raphe nuclei . Norepinephrine , which is involved in arousal, comes exclusively from a nearby small area called the locus coeruleus . Other neurotransmitters such as acetylcholine and dopamine have multiple sources in
SECTION 60
#17328513219956200-431: The brains of animals such as rats, show that the brain of a living animal is constantly active, even during sleep. Each part of the brain shows a mixture of rhythmic and nonrhythmic activity, which may vary according to behavioral state. In mammals, the cerebral cortex tends to show large slow delta waves during sleep, faster alpha waves when the animal is awake but inattentive, and chaotic-looking irregular activity when
6300-549: The cerebral cortex were magnified so that its cell body became the size of a human body, its axon, equally magnified, would become a cable a few centimeters in diameter, extending more than a kilometer. These axons transmit signals in the form of electrochemical pulses called action potentials, which last less than a thousandth of a second and travel along the axon at speeds of 1–100 meters per second. Some neurons emit action potentials constantly, at rates of 10–100 per second, usually in irregular patterns; other neurons are quiet most of
6400-503: The cerebral cortex. The cerebellum of mammals contains a large portion (the neocerebellum ) dedicated to supporting the cerebral cortex, which has no counterpart in other vertebrates. In placental mammals , there is a wide nerve tract connecting the cerebral hemispheres called the corpus callosum . The brains of humans and other primates contain the same structures as the brains of other mammals, but are generally larger in proportion to body size. The encephalization quotient (EQ)
6500-507: The coordination of motor control ( muscle activity and endocrine system ). While invertebrate brains arise from paired segmental ganglia (each of which is only responsible for the respective body segment ) of the ventral nerve cord , vertebrate brains develop axially from the midline dorsal nerve cord as a vesicular enlargement at the rostral end of the neural tube , with centralized control over all body segments. All vertebrate brains can be embryonically divided into three parts:
6600-512: The darker-colored grey matter that marks areas with high densities of neuron cell bodies. Except for a few primitive organisms such as sponges (which have no nervous system) and cnidarians (which have a diffuse nervous system consisting of a nerve net ), all living multicellular animals are bilaterians , meaning animals with a bilaterally symmetric body plan (that is, left and right sides that are approximate mirror images of each other). All bilaterians are thought to have descended from
6700-420: The developing brain, and apparently exist solely to guide development. In humans and many other mammals, new neurons are created mainly before birth, and the infant brain contains substantially more neurons than the adult brain. There are, however, a few areas where new neurons continue to be generated throughout life. The two areas for which adult neurogenesis is well established are the olfactory bulb, which
6800-412: The early stages of neural development are similar across all species. As the embryo transforms from a round blob of cells into a wormlike structure, a narrow strip of ectoderm running along the midline of the back is induced to become the neural plate , the precursor of the nervous system. The neural plate folds inward to form the neural groove , and then the lips that line the groove merge to enclose
6900-434: The edge of the neocortex, including the hippocampus and amygdala , are also much more extensively developed in mammals than in other vertebrates. The elaboration of the cerebral cortex carries with it changes to other brain areas. The superior colliculus , which plays a major role in visual control of behavior in most vertebrates, shrinks to a small size in mammals, and many of its functions are taken over by visual areas of
7000-431: The environment), and the processing of novelty. The P3b has a positive-going amplitude (usually relative to a reference behind the ear or the average of two such references) that peaks at around 300 ms, and the peak will vary in latency from 250 to 500 ms or more, depending upon the task and the individual subject response. Amplitudes are typically highest on the scalp over parietal brain areas. The P3b has been
7100-428: The fact that the numbers were meaningful to the participants, based on the task that they were asked to perform. In 1965, Sutton and colleagues published results from two experiments that further explored this late positivity. They presented subjects with either a cue that indicated whether the following stimulus would be a click or a flash, or a cue which required subjects to guess whether the following stimulus would be
7200-467: The forebrain becomes much larger than the other parts, the hindbrain develops a bulky dorsal extension known as the cerebellum , and the midbrain becomes very small as a result. The brains of vertebrates are made of very soft tissue. Living brain tissue is pinkish on the outside and mostly white on the inside, with subtle variations in color. Vertebrate brains are surrounded by a system of connective tissue membranes called meninges , which separate
7300-424: The forebrain, which is greatly enlarged and also altered in structure. The cerebral cortex is the part of the brain that most strongly distinguishes mammals. In non-mammalian vertebrates, the surface of the cerebrum is lined with a comparatively simple three-layered structure called the pallium . In mammals, the pallium evolves into a complex six-layered structure called neocortex or isocortex . Several areas at
7400-436: The improbable event could be an infrequent target letter in a stream of letters, to which a subject might respond with a button press). The P3b can also be used to measure how demanding a task is on cognitive workload . Since the initial discovery of the P300, research has shown that the P300 has two subcomponents. The subcomponents are the novelty P3, or P3a , and the classic P300, which has since been renamed P3b . Since
7500-412: The late positivity occurred 300 ms after the second click. This shows two important findings: first, that this late positivity occurred when uncertainty about the type of click was resolved, and second, that even an absence of a stimulus would elicit the late positive complex, if said stimulus was relevant to the task. These early studies encouraged the use of ERP methods to study cognition and provided
7600-441: The map, leaving it finally in its precise adult form. Similar things happen in other brain areas: an initial synaptic matrix is generated as a result of genetically determined chemical guidance, but then gradually refined by activity-dependent mechanisms, partly driven by internal dynamics, partly by external sensory inputs. In some cases, as with the retina-midbrain system, activity patterns depend on mechanisms that operate only in
7700-407: The membrane of the synapse's target cell (or cells), and thereby alter the electrical or chemical properties of the receptor molecules. With few exceptions, each neuron in the brain releases the same chemical neurotransmitter, or combination of neurotransmitters, at all the synaptic connections it makes with other neurons; this rule is known as Dale's principle . Thus, a neuron can be characterized by
7800-440: The membrane of the target cell. Synapses are the key functional elements of the brain. The essential function of the brain is cell-to-cell communication , and synapses are the points at which communication occurs. The human brain has been estimated to contain approximately 100 trillion synapses; even the brain of a fruit fly contains several million. The functions of these synapses are very diverse: some are excitatory (exciting
7900-440: The mid-1980s, one of the most discussed uses of ERPs such as the P300 is related to lie detection . In a proposed "guilty knowledge test" a subject is interrogated via the oddball paradigm much as they would be in a typical lie-detector situation. This practice has recently enjoyed increased legal permissibility while conventional polygraphy has seen its use diminish, in part owing to the unconscious and uncontrollable aspects of
8000-494: The neurotransmitters that it releases. The great majority of psychoactive drugs exert their effects by altering specific neurotransmitter systems. This applies to drugs such as cannabinoids , nicotine , heroin , cocaine , alcohol , fluoxetine , chlorpromazine , and many others. The two neurotransmitters that are most widely found in the vertebrate brain are glutamate , which almost always exerts excitatory effects on target neurons, and gamma-aminobutyric acid (GABA), which
8100-722: The organization of the spinal cord and cranial nerve, as well as elaborated brain pattern of organization. Elaborated brains are characterized by migrated neuronal cell bodies away from the periventricular matrix, region of neuronal development, forming organized nuclear groups. Aside from reptiles and mammals , other vertebrates with elaborated brains include hagfish , galeomorph sharks , skates , rays , teleosts , and birds . Overall elaborated brains are subdivided in forebrain, midbrain, and hindbrain. The hindbrain coordinates and integrates sensory and motor inputs and outputs responsible for, but not limited to, walking, swimming, or flying. It contains input and output axons interconnecting
8200-406: The pallium are associated with perception , learning , and cognition . Beneath the pallium are the two components of the subpallium, the striatum and pallidum . The subpallium connects different parts of the telencephalon and plays major roles in a number of critical behaviours. To the rear of the telencephalon are the thalamus , midbrain , and cerebellum . The hindbrain connects the rest of
8300-430: The passage of many toxins and pathogens (though at the same time blocking antibodies and some drugs, thereby presenting special challenges in treatment of diseases of the brain). As a result of the osmotic restriction by the blood-brain barrier, the metabolites within the brain are cleared mostly by bulk flow of the cerebrospinal fluid within the glymphatic system instead of via venules like other parts of
8400-564: The primate brain comes from a massive expansion of the cerebral cortex, especially the prefrontal cortex and the parts of the cortex involved in vision . The visual processing network of primates includes at least 30 distinguishable brain areas, with a complex web of interconnections. It has been estimated that visual processing areas occupy more than half of the total surface of the primate neocortex. The prefrontal cortex carries out functions that include planning , working memory , motivation , attention , and executive control . It takes up
8500-439: The qualities of mind , personality, and intelligence can be attributed to heredity or to upbringing . Although many details remain to be settled, neuroscience shows that both factors are important. Genes determine both the general form of the brain and how it reacts to experience, but experience is required to refine the matrix of synaptic connections, resulting in greatly increased complexity. The presence or absence of experience
8600-577: The reproducibility and ubiquity of this signal makes it a common choice for psychological tests in both the clinic and laboratory. Early observations of the P300 (more specifically, the component that would later be named the P3b) were reported in the mid-1960s. In 1964, researchers Chapman and Bragdon found that ERP responses to visual stimuli differed depending on whether the stimuli had meaning or not. They showed subjects two kinds of visual stimuli: numbers and flashes of light. Subjects viewed these stimuli one at
8700-413: The rest of the body. Like in all chordates , the avian brain is contained within the skull bones of the head . The bird brain is divided into a number of sections, each with a different function. The cerebrum or telencephalon is divided into two hemispheres , and controls higher functions. The telencephalon is dominated by a large pallium , which corresponds to the mammalian cerebral cortex and
8800-433: The right general vicinity in the midbrain by chemical cues, but then branches very profusely and makes initial contact with a wide swath of midbrain neurons. The retina, before birth, contains special mechanisms that cause it to generate waves of activity that originate spontaneously at a random point and then propagate slowly across the retinal layer. These waves are useful because they cause neighboring neurons to be active at
8900-588: The same basic components are present in all vertebrate brains, some branches of vertebrate evolution have led to substantial distortions of brain geometry, especially in the forebrain area. The brain of a shark shows the basic components in a straightforward way, but in teleost fishes (the great majority of existing fish species), the forebrain has become "everted", like a sock turned inside out. In birds, there are also major changes in forebrain structure. These distortions can make it difficult to match brain components from one species with those of another species. Here
9000-400: The same time; that is, they produce a neural activity pattern that contains information about the spatial arrangement of the neurons. This information is exploited in the midbrain by a mechanism that causes synapses to weaken, and eventually vanish, if activity in an axon is not followed by activity of the target cell. The result of this sophisticated process is a gradual tuning and tightening of
9100-510: The same title formed as a letter–number combination. If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=P300&oldid=495817377 " Category : Letter–number combination disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages P300 (neuroscience) It
9200-605: The smallest. Turtles have the largest diencephalon per body weight whereas crocodilians have the smallest. On the other hand, lizards have the largest mesencephalon. Yet their brains share several characteristics revealed by recent anatomical, molecular, and ontogenetic studies. Vertebrates share the highest levels of similarities during embryological development, controlled by conserved transcription factors and signaling centers , including gene expression, morphological and cell type differentiation. In fact, high levels of transcriptional factors can be found in all areas of
9300-500: The species diversity, reptiles have diverged in terms of external morphology, from limbless to tetrapod gliders to armored chelonians , reflecting adaptive radiation to a diverse array of environments. Morphological differences are reflected in the nervous system phenotype , such as: absence of lateral motor column neurons in snakes, which innervate limb muscles controlling limb movements; absence of motor neurons that innervate trunk muscles in tortoises; presence of innervation from
9400-419: The spinal cord, midbrain and forebrain transmitting information from the external and internal environments. The midbrain links sensory, motor, and integrative components received from the hindbrain, connecting it to the forebrain. The tectum, which includes the optic tectum and torus semicircularis, receives auditory, visual, and somatosensory inputs, forming integrated maps of the sensory and visual space around
9500-415: The stimulus (auditory or visual) did not matter. In later studies published in 1967, Sutton and colleagues had subjects guess whether they would hear one click or two clicks. They again observed a positivity around 300 ms after the second click occurred – or would have occurred, in the case of the single click. They also had subjects guess how long the interval between clicks might be, and in this case,
9600-426: The subject, and various columns or rows are highlighted. When a column or row contains the character a subject desires to communicate, the P300 response is elicited (since this character is "special" it is the target stimulus described in the typical oddball paradigm). The combination of the row and column which evoked the response locates the desired character. A number of such trials must be averaged to clear noise from
9700-423: The target cell); others are inhibitory; others work by activating second messenger systems that change the internal chemistry of their target cells in complex ways. A large number of synapses are dynamically modifiable; that is, they are capable of changing strength in a way that is controlled by the patterns of signals that pass through them. It is widely believed that activity-dependent modification of synapses
9800-440: The time, but occasionally emit a burst of action potentials. Axons transmit signals to other neurons by means of specialized junctions called synapses . A single axon may make as many as several thousand synaptic connections with other cells. When an action potential, traveling along an axon, arrives at a synapse, it causes a chemical called a neurotransmitter to be released. The neurotransmitter binds to receptor molecules in
9900-427: The tissue to reach their ultimate locations. Once neurons have positioned themselves, their axons sprout and navigate through the brain, branching and extending as they go, until the tips reach their targets and form synaptic connections. In a number of parts of the nervous system, neurons and synapses are produced in excessive numbers during the early stages, and then the unneeded ones are pruned away. For vertebrates,
10000-413: The trigeminal nerve to pit organs responsible to infrared detection in snakes. Variation in size, weight, and shape of the brain can be found within reptiles. For instance, crocodilians have the largest brain volume to body weight proportion, followed by turtles, lizards, and snakes. Reptiles vary in the investment in different brain sections. Crocodilians have the largest telencephalon, while snakes have
#994005