Cognitive Neuroscience Exam Two

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Achromatopsia

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a medical syndrome that exhibits symptoms relating to at least five separate individual diseases. Although the term may refer to acquired disorders such as color agnosia and cerebral achromatopsia, it typically refers to an autosomal recessive congenital color vision disorder, the inability to perceive color AND to achieve satisfactory visual acuity at high light levels (typically exterior daylight). The syndrome is also present in an incomplete form which is more properly defined as dyschromatopsia. The only estimate of its relative occurrence of 1:33,000 in the general population dates from the 1960s or earlier.

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Akinetopsia

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known as cerebral akinetopsia or motion blindness, is an extremely rare neuropsychological disorder in which a patient cannot perceive motion in their visual field, despite being able to see stationary objects without issue. Most of what is known about akinetopsia was learned through the case study of one patient, LM. There is currently no effective treatment or cure for akinetopsia.

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Area MT

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Visual area V5, also known as visual area MT (middle temporal), is a region of extrastriate visual cortex that is thought to play a major role in the perception of motion, the integration of local motion signals into global percepts and the guidance of some eye movements.[17]
[edit]Connections
MT is connected to a wide array of cortical and subcortical brain areas. Its inputs include the visual cortical areas V1, V2, and dorsal V3 (dorsomedial area),[18][19] the koniocellular regions of the LGN,[20] and the inferior pulvinar. The pattern of projections to MT changes somewhat between the representations of the foveal and peripheral visual fields, with the latter receiving inputs from areas located in the midline cortex and retrosplenial region [21]
A standard view is that V1 provides the "most important" input to MT.[17] Nonetheless, several studies have demonstrated that neurons in MT are capable of responding to visual information, often in a direction-selective manner, even after V1 has been destroyed or inactivated.[22] Moreover, research by Semir Zeki and collaborators has suggested that certain types of visual information may reach MT before it even reaches V1.
MT sends its major outputs to areas located in the cortex immediately surrounding it, including areas FST, MST and V4t (middle temporal crescent). Other projections of MT target the eye movement-related areas of the frontal and parietal lobes (frontal eye field and lateral intraparietal area).

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Area V4

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The color selectivity of area V4 was central to the original formation of the "one-area-one-function" hypothesis, and has always been an area of debate(5). In 1973, Zeki(4) first reported highly selective sensitivity to color when recording from single cells in V4. Later investigations of V4 found widely disparate levels of color selectivity. Then, Schein and Desimone(8) reported that V4 cells responded very broadly to colored stimuli, and that this broad response was probably responsible for the widely varying reports of the extent of color selectivity in V4.

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Blindsight

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a phenomenon in which people who are perceptually blind in a certain area of their visual field demonstrate some response to visual stimuli.[1][2] In Type 1 blindsight subjects have no awareness whatsoever of any stimuli, but yet are able to predict, at levels significantly above chance, aspects of a visual stimulus, such as location, or type of movement, often in a forced-response or guessing situation. Type 2 blindsight is when subjects have some awareness of, for example, movement within the blind area, but no visual percept. This may be caused by, for example, the person being aware of their eyes' tracking motion which will function normally. Blindsight is caused by injury to the part of the brain responsible for vision (see occipital lobe). Evidence for it can be indirectly observed in children as young as two months, although it is difficult to determine the type in a person who is not old enough to answer questions.[3]

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Chemical Senses

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Three sensory systems associated with the nose and mouth—olfaction, taste, and the trigeminal chemosensory system—are dedicated to the detection of chemicals in the environment. The olfactory system detects airborne molecules called odors. In humans, odors provide information about food, self, other people, animals, plants, and many other aspects of the environment. Olfactory information can influence feeding behavior, social interactions and, in many animals, reproduction. The taste (or gustatory) system detects ingested, primarily water-soluble molecules called tastants. Tastants provide information about the quality, quantity, pleasantness, and safety of ingested food. The trigeminal chemosensory system provides information about irritating or noxious molecules that come into contact with skin or mucous membranes of the eyes, nose and mouth. All three of these chemosensory systems rely on receptors in the nasal cavity, mouth, or on the face that interact with the relevant molecules and generate receptor and action potentials, thus transmitting the effects of chemical stimuli to appropriate regions of the central nervous system.

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Cochlear Nucleus

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consist of:
(a) the dorsal cochlear nucleus (DCN), corresponding to the tuberculum acusticum on the dorso-lateral surface of the inferior peduncle; and
(b) the ventral or accessory cochlear nucleus, placed between the two divisions of the nerve, on the ventral aspect of the inferior peduncle.
The ventral cochlear nucleus is further divided into the posteroventral cochlear nucleus (PVCN) and the anteroventral cochlear nucleus (AVCN).[1]
The cochlear nucleus receives input from somatosensory parts of the brain.[2]

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Corpuscle

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Pacinian corpuscles are one of the four major types of mechanoreceptor. They are nerve endings in the skin, responsible for sensitivity to pain and pressure.
Similar in physiology to the Meissner's corpuscle, Pacinian corpuscles are larger and fewer in number than both Merkel cells and Meissner's corpuscles[1] .

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Cortical Visual Areas

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The primary visual cortex is the best studied visual area in the brain. In all mammals studied, it is located in the posterior pole of the occipital cortex (the occipital cortex is responsible for processing visual stimuli). It is the simplest, earliest cortical visual area. It is highly specialized for processing information about static and moving objects and is excellent in pattern recognition.

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Extrastriate Visual Areas

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the region of the occipital cortex of the mammalian brain located next to the striate cortex (which is also known as the primary visual cortex). In terms of Brodmann areas, the extrastriate cortex comprises Brodmann area 18 and Brodmann area 19, while the striate cortex comprises Brodmann area 17.
In primates, the extrastriate cortex includes visual area V2, visual area V3, visual area V4, visual area MT (sometimes called V5), and visual area DP.
The extrastriate cortex is the locus of mid-level vision. Neurons in the extrastriate cortex generally respond to visual stimuli within their receptive fields. These responses are modulated by extraretinal effects, like attention, working memory, and reward expectation.

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Glomeruli

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a spherical structure located in the olfactory bulb of the brain where the synapses form between the olfactory nerve terminals and dendrites of mitral, periglomerular and tufted cells. Each glomerulus is surrounded by periglomerular neurons and glial cells which gives it an oval shape.[1][2] All glomeruli are located near the surface of the olfactory bulb. In mammals, glomeruli typically range between 50-120 µm in diameter and number between 1800 and 2400 depending on the species.[1][2] Each glomerulus is composed of two compartments, the olfactory nerve zone and the non-olfactory nerve zone. The olfactory nerve zone is composed of preterminals and terminals of the olfactory nerve and is where the olfactory receptor cells make synapses on their targets.[2] The non-olfactory nerve zone is composed of the dendritic processes of intrinsic neurons and is where dendrodendritic interactions between intrinsic neurons occur.[2] It is the first site for synaptic processing of odor information coming from the nose. It is made up of a globular tangle of axons from the olfactory receptor neurons in the olfactory epithelium, and dendrites from the mitral cell as well as from juxtaglomerular cells that include tufted cells, periglomerular cells, short axon cells, and astrocytes.

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Hemianopia

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impairment of the sense of sight

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Inferior Colliculus

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the principal midbrain nucleus of the auditory pathway and receives input from several more peripheral brainstem nuclei in the auditory pathway, as well as inputs from the auditory cortex.[1] The inferior colliculus has three subdivisions: the central nucleus (CIC), a dorsal cortex (DCIC) by which it is surrounded, and an external cortex (ICX) which is located laterally.[2] Its bimodal neurons are implied in auditory-somatosensory interaction, receiving projections from somatosensory nuclei. This multisensory integration may underlie a filtering of self-effected sounds from vocalisation, chewing, or respiration activities.[3]

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Interaural Time

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when concerning humans or animals, is the difference in arrival time of a sound between two ears. It is important in the localisation of sounds, as it provides a cue to the direction or angle of the sound source from the head. When a signal is produced in the horizontal plane, its angle in relation to the head is referred to as its azimuth, with 0 degrees (0°) azimuth being directly in front of the listener, 90° to the right, and 180° being directly behind. If a signal arrives at the head from 90° azimuth, the signal has further to travel to reach the left ear than the right. This results in a time difference between when the sound reached either ear. This is detected, and aids the process of identifying the sound source.

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Lateral Geniculate Nucleus (LGN)

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the primary processing center for visual information received from the retina of the eye. The LGN is found inside the thalamus of the brain, and is thus part of the central nervous system.
The LGN receives information directly from the ascending retinal ganglion cells via the optic tract and from the reticular activating system. Neurons of the LGN send their axons through the optic radiation, a pathway directly to the primary visual cortex (or V1), also known as the striate cortex. The primary visual cortex surrounds the calcarine fissure, a horizontal fissure in the medial and posterior occipital lobe.[1] In addition, the LGN receives many strong feedback connections from the primary visual cortex. In mammals and humans the two strongest pathways linking the eye to the brain are those projecting to the LGNd (dorsal part of the LGN in the thalamus), and to the Superior Colliculus (SC)[2]

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Medial Geniculate Nucleus (MGN)

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part of the auditory thalamus and represents the thalamic relay between the inferior colliculus (IC) and the auditory cortex (AC). It is made up of a number of sub-nuclei that are distinguished by their neuronal morphology and density, by their afferent and efferent connections, and by the coding properties of their neurons. It is thought that the MGB influences the direction and maintenance of attention.

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Multisensory Integration

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known as 'multisensory integration' is the study of how information from the different sensory modalities, such as sight, sound, touch, smell, self-motion and taste, may be integrated by the nervous system. A coherent representation of objects combining modalities enables us to have meaningful perceptual experiences. Indeed, multisensory integration is central to adaptive behavior because it allows us to perceive a world of coherent perceptual entities.[1] Multimodal integration also deals with how different sensory modalities interact with one another and alter each other’s processing.

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Nociceptors

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a sensory receptor that responds to potentially damaging stimuli by sending nerve signals to the spinal cord and brain. This process, called nociception, usually causes the perception of pain.

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Odorant

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known as odorant, aroma, fragrance or flavor, is a chemical compound that has a smell or odor. A chemical compound has a smell or odor when two conditions are met: the compound needs to be volatile, so it can be transported to the olfactory system in the upper part of the nose, and it needs to be in a sufficiently high concentration to be able to interact with one or more of the olfactory receptors.

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Photoreceptors

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a specialized type of neuron (nerve cell) found in the eye's retina that is capable of phototransduction. The great biological importance of photoreceptors is that as cells they convert light (electromagnetic radiation) into the beginning of a chain of biological processes. More specifically, the photoreceptor absorbs photons from the field of view, and through a specific and complex biochemical pathway, signals this information through a change in its membrane potential.
For hundreds of years, photoreceptors in vertebrates were thought to be of only two main classes. The two classic photoreceptors are rods and cones, each contributing information used by the visual system to form a representation of the visual world, sight.

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Primary Auditory Cortex (A1)

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the region of the brain that is responsible for processing of auditory (sound) information. It is located on the temporal lobe, and performs the basics of hearing; pitch and volume.

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Primary Olfactory Cortex

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a portion of the cortex involved in olfaction.[1][2][3]
Some sources state that it includes the prepyriform area and entorhinal area.[4]
Other sources state that it consists of the prepiriform cortex and periamygdaloid cortex.[5]

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Primary Somatosensory Cortex (S1)

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Brodmann areas 3, 1 and 2 comprise the primary somatosensory cortex of the human brain (or S1). Because Brodmann sliced the brain somewhat obliquely, he encountered area 1 first; however, from rostral to caudal the Brodmann designations are 3, 1 and 2, respectively.

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Primary Visual Cortex (V1)

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refers to the primary visual cortex (also known as striate cortex or V1) and extrastriate visual cortical areas such as V2, V3, V4, and V5. The primary visual cortex is anatomically equivalent to Brodmann area 17, or BA17. The extrastriate cortical areas consist of Brodmann area 18 and Brodmann area 19. There is a visual cortex for each hemisphere of the brain. The left hemisphere visual cortex receives signals from the right visual field and the right visual cortex from the left visual field. The body of this article describes the primate (especially, human) visual cortex.

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Retina

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a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses. These are sent to various visual centers of the brain through the fibers of the optic nerve.
In vertebrate embryonic development, the retina and the optic nerve originate as outgrowths of the developing brain, so the retina is considered part of the central nervous system (CNS).[1] It is the only part of the CNS that can be visualized non-invasively.

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Scotoma

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an area of partial alteration in one's field of vision consisting in a partially diminished or entirely degenerated visual acuity which is surrounded by a field of normal - or relatively well-preserved - vision.


Example image showing normal field of vision.


Example image showing small, deep central scotoma, as may be caused by age-related maculopathy.


Example image showing a peripheral ring scotoma, as may be caused by retinitis pigmentosa.


Example of a scintillating scotoma, as may be caused by cortical spreading depression.
Every normal mammalian eye has a scotoma in its field of vision, usually termed its blind spot. This is a location with no photoreceptor cells, where the retinal ganglion cell axons that comprise the optic nerve exit the retina. This location is called the optic disc. When both eyes are open, visual signals that are absent in the blind spot of one eye are provided from the opposite visual cortex for the other eye, even when the other eye is closed. The absence of visual imagery from the blindspot does not intrude into consciousness with one eye closed, because the corresponding visual field locations of the optic discs in the two eyes differ.

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Secondary Somatosensory Cortex (S2)

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a region of cerebral cortex lying mostly on the parietal operculum.
Region S2 was first described by Adrian in 1940, who found that feeling in cats' feet was not only represented in the previously described primary somatosensory cortex (S1) but also in a second region adjacent to S1.[1] In 1954, Penfield and Jasper evoked somatosensory sensations in human patients during neurosurgery using electrical stimulation in the lateral sulcus, which lies adjacent to S1, and their findings were confirmed in 1979 by Woolsey et al. using evoked potentials and electrical stimulation.[2][3] Functional neuroimaging studies have found S2 activation in response to light touch, pain, visceral sensation, and tactile attention.[4]

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Superiour Colliculus

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a paired structure that forms a major component of the vertebrate midbrain. In mammals this structure is more commonly called the superior colliculus (Latin, higher hill), but, even in mammals, the adjective tectal is commonly used. The tectum is a layered structure, with a number of layers that vary by species. The superficial layers are sensory-related, and receive input from the eyes as well as other sensory systems.[1] The deep layers are motor-related, capable of activating eye movements as well as other responses. There are also intermediate layers, with multi-sensory cells and motor properties.
The general function of the tectal system is to direct behavioral responses toward specific points in egocentric ("body-centered") space. Each layer of the tectum contains a topographic map of the surrounding world in retinotopic coordinates, and activation of neurons at a particular point in the map evokes a response directed toward the corresponding point in space. In primates, the tectum ("superior colliculus") has been studied mainly with respect to its role in directing eye movements. Visual input from the retina, or "command" input from the cerebral cortex, create a "bump" of activity in the tectal map, which, if strong enough, induces a saccadic eye movement. Even in primates, however, the tectum is also involved in generating spatially directed head turns, arm-reaching movements,[2] and shifts in attention that do not involve any overt movements.[3]

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Synesthesia

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"sensation"—is a neurologically-based condition in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway.[1][2][3][4] People who report such experiences are known as synesthetes.

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Tastant

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Any chemical that stimulates the sensory cells in a taste bud.

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Proprioception

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meaning "one's own" and perception, is the sense of the relative position of neighbouring parts of the body. Unlike the exteroceptive senses by which we perceive the outside world, and interoceptive senses, by which we perceive the pain and movement of internal organs, proprioception is a third distinct sensory modality that provides feedback solely on the status of the body internally. It is the sense that indicates whether the body is moving with required effort, as well as where the various parts of the body are located in relation to each other.

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Thalamus

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a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections. Its function includes relaying sensation, spatial sense and motor signals to the cerebral cortex, along with the regulation of consciousness, sleep and alertness. The thalamus surrounds the third ventricle. It is the main product of the embryonic diencephalon.