The retrosplenial cortex is a cortical area in the brain, located posteriorly and comprising Brodmann areas 29 and 30. The region's name refers to its anatomical location behind the splenium of the corpus callosum in primates, although in rodents it is located more towards the brain surface and is larger, its function is not well understood, but its location close to visual areas and to the hippocampal spatial/memory system suggest it may have a role in mediating between perceptual and memory functions. There is a large amount of variation in the region's size across different species. In humans it comprises 0.3% of the entire cortical surface whereas in rabbits it is at least 10% and in rats it extends for more than half the cerebrum dorso-ventrally, making it one of the largest cortical regions. On the basis of its microscopic cellular structure it is divided into dysgranular and granular regions; the retrosplenial cortex has dense reciprocal projections with the visual cortex and with anterior thalamic nuclei and the hippocampus.
Neurophysiological studies of retrosplenial cortex have been done in rats. In rodents, around 8.5% of neurons in the retrosplenial cortex are head direction cells while other neurons have correlates with movement parameters such as running speed, there is evidence of weak spatial coding. Much of the observed activity has been found to be conjunctive. A recent study of rats running on a long linear maze found complex patterns of activity reflecting conjunctions between position on the track, position on the track within the room at large and whether the animal was turning left or right. In humans, fMRI studies implicate the retrosplenial cortex in a wide range of cognitive functions including episodic memory, imagining future events and processing scenes more generally. Rodent studies suggest the region is important for using surrounding visual cues to carry out these tasks. Retrosplenial cortex is responsive to permanent, non-moving environmental landmarks and is implicated in using them to make spatial judgements.
It has been suggested that retrosplenial cortex may translate between egocentric and allocentric spatial information, based upon its anatomical location between the hippocampus and the parietal lobe. Competitors in the World Memory Championships are able to perform outstanding feats of memory and show increased fMRI activation in their retrosplenial cortex than normal controls when doing so; this is thought to be due to their use of a spatial learning strategy or mnemonic device known as the method of loci. The region displays slow-wave theta rhythmicity and when people retrieve autobiographical memories, there is theta band interaction between the retrosplenial cortex and the medial temporal lobe; the retrosplenial cortex is one of several brain areas that produces both an anterograde and retrograde amnesia when damaged. People with lesions involving the retrosplenial cortex display a form of topographical disorientation whereby they can recognise and identify environmental landmarks, but are unable to use them to orientate themselves.
The retrosplenial cortex is one of the first regions to undergo pathological changes in Alzheimer's disease and its prodromal phase of mild cognitive impairment
Brodmann area 6
Brodmann area 6 part of the frontal cortex in the human brain. Situated just anterior to the primary motor cortex, it is composed of the premotor cortex and, the supplementary motor area, or SMA; this large area of the frontal cortex is believed to play a role in the planning of complex, coordinated movements. Brodmann area 6 is called agranular frontal area 6 in humans because it lacks an internal granular cortical layer, it is a subdivision of the cytoarchitecturally defined precentral region of cerebral cortex. In the human brain, it is located on the portions of the precentral gyrus that are not occupied by Brodmann area 4, it extends from the cingulate sulcus on the medial aspect of the hemisphere to the lateral sulcus on the lateral aspect. It is bounded rostrally by the granular frontal region and caudally by the gigantopyramidal area 4. Brodmann area 6 is a cytoarchitecturally defined portion of the frontal lobe of the guenon. Brodmann-1909 regarded it as topographically and cytoarchitecturally homologous to the human agranular frontal area 6 and noted that, in the monkey, area 4 is larger than area 6, whereas, in the human, area 6 is larger than area 4.
Distinctive features: It is thick relative to other cortical areas. Brodmann area List of regions in the human brain Korbinian Brodmann ancil-41 at NeuroNames – agranular frontal area 6 ancil-1044 at NeuroNames – Brodmann area 6
Brodmann area 12
Brodmann area 12 is a subdivision of the cerebral cortex of the guenon defined on the basis of cytoarchitecture. It occupies the most rostral portion of the frontal lobe. Brodmann-1909 did not regard it as homologous, either topographically or cytoarchitecturally, to rostral area 12 of the human. Distinctive features: a quite distinct internal granular layer separates slender pyramidal cells of the external pyramidal layer and the internal pyramidal layer, it is indirectly connected to the global palladius as well as the substantia nigra, due to efferents to the striatum. Glutaminergic input is turned into GABAergic input there, which allows the frontal lobes to exhibit some control over basal ganglia activity. Brodmann area List of regions in the human brain For Neuroanatomy of this area see BrainInfo
Brodmann area 44
Brodmann area 44, or BA44, is part of the frontal cortex in the human brain. Situated just anterior to premotor cortex and on the lateral surface, inferior to BA9; this area is known as pars opercularis, it refers to a subdivision of the cytoarchitecturally defined frontal region of cerebral cortex. In the human it corresponds to the opercular part of the inferior frontal gyrus. Thus, it is bounded caudally by the inferior precentral sulcus and rostrally by the anterior ascending limb of lateral sulcus, it surrounds the diagonal sulcus. In the depth of the lateral sulcus it borders on the insula. Cytoarchitectonically it is bounded caudally and dorsally by the agranular frontal area 6, dorsally by the granular frontal area 9 and rostrally by the triangular part of inferior frontal gyrus. Together with left-hemisphere BA 45, the left hemisphere BA 44 comprises Broca's area, a region involved in semantic tasks; some data suggest. Some recent findings suggest the implication of this region in music perception.
Recent neuroimaging studies show BA44 involvement in selective response suppression in go/no- go tasks and is therefore believed to play an important role in the suppression of response tendencies. Neuroimaging studies demonstrate that area 44 is related to hand movements. Scott Flansburg of San Diego, California is a "human calculator" who can perform complex arithmetic in his head. Profiled on the TV show Stan Lee's Superhumans, his brain was scanned using fMRI while doing complex calculations, which showed brain activity in this region was absent. Instead there was activity closer to the motor cortex. Brodmann area List of regions in the human brain For Neuroanatomy of this area visit BrainInfo
The visual cortex of the brain is that part of the cerebral cortex which processes visual information. It is located in the occipital lobe. Visual nerves run straight from the eye to the primary visual cortex to the Visual Association cortex. Visual information coming from the eye goes through the lateral geniculate nucleus in the thalamus and reaches the visual cortex; the part of the visual cortex that receives the sensory inputs from the thalamus is the primary visual cortex known as visual area 1, the striate cortex. The extrastriate areas consist of visual areas 2, 3, 4, 5. Both hemispheres of the brain contain a visual cortex; the primary visual cortex is located around the calcarine fissure in the occipital lobe. Each hemisphere's V1 receives information directly from its ipsilateral lateral geniculate nucleus that receives signals from the contralateral visual hemifield. Neurons in the visual cortex fire action potentials when visual stimuli appear within their receptive field. By definition, the receptive field is the region within the entire visual field that elicits an action potential.
But, for any given neuron, it may respond best to a subset of stimuli within its receptive field. This property is called neuronal tuning. In the earlier visual areas, neurons have simpler tuning. For example, a neuron in V1 may fire to any vertical stimulus in its receptive field. In the higher visual areas, neurons have complex tuning. For example, in the inferior temporal cortex, a neuron may fire only when a certain face appears in its receptive field; the visual cortex receives its blood supply from the calcarine branch of the posterior cerebral artery. V1 transmits information to two primary pathways, called the dorsal stream; the ventral stream begins with V1, goes through visual area V2 through visual area V4, to the inferior temporal cortex. The ventral stream, sometimes called the "What Pathway", is associated with form recognition and object representation, it is associated with storage of long-term memory. The dorsal stream begins with V1, goes through Visual area V2 to the dorsomedial area and Visual area MT and to the posterior parietal cortex.
The dorsal stream, sometimes called the "Where Pathway" or "How Pathway", is associated with motion, representation of object locations, control of the eyes and arms when visual information is used to guide saccades or reaching. The what vs. where account of the ventral/dorsal pathways was first described by Ungerleider and Mishkin. More Goodale and Milner extended these ideas and suggested that the ventral stream is critical for visual perception whereas the dorsal stream mediates the visual control of skilled actions, it has been shown that visual illusions such as the Ebbinghaus illusion distort judgements of a perceptual nature, but when the subject responds with an action, such as grasping, no distortion occurs. Work such as the one from Scharnowski and Gegenfurtner suggests that both the action and perception systems are fooled by such illusions. Other studies, provide strong support for the idea that skilled actions such as grasping are not affected by pictorial illusions and suggest that the action/perception dissociation is a useful way to characterize the functional division of labor between the dorsal and ventral visual pathways in the cerebral cortex.
The primary visual cortex is the most studied visual area in the brain. In mammals, it is located in the posterior pole of the occipital lobe and is the simplest, earliest cortical visual area, it is specialized for processing information about static and moving objects and is excellent in pattern recognition. The functionally defined primary visual cortex is equivalent to the anatomically defined striate cortex; the name "striate cortex" is derived from the line of Gennari, a distinctive stripe visible to the naked eye that represents myelinated axons from the lateral geniculate body terminating in layer 4 of the gray matter. The primary visual cortex is divided into six functionally distinct layers, labeled 1 to 6. Layer 4, which receives most visual input from the lateral geniculate nucleus, is further divided into 4 layers, labelled 4A, 4B, 4Cα, 4Cβ. Sublamina 4Cα receives magnocellular input from the LGN, while layer 4Cβ receives input from parvocellular pathways; the average number of neurons in the adult human primary visual cortex in each hemisphere has been estimated at around 140 million.
The tuning properties of V1 neurons differ over time. Early in time individual V1 neurons have strong tuning to a small set of stimuli; that is, the neuronal responses can discriminate small changes in visual orientations, spatial frequencies and colors. Furthermore, individual V1 neurons in humans and animals with binocular vision have ocular dominance, namely tuning to one of the two eyes. In V1, primary sensory cortex in general, neurons with similar tuning properties tend to cluster together as cortical columns. David Hubel and Torsten Wiesel proposed the classic ice-cube organization model of cortical columns for two tuning properties: ocular dominance and orientation. However, this model cannot accommodate the color, spatial frequency and many other features to which neurons are tuned; the exact organization of all these cortical columns within V1 remains a hot topic of current research. The mathematical modeling of this function has been compared t
Brodmann area 19
Brodmann area 19, or BA 19, is part of the occipital lobe cortex in the human brain. Along with area 18, it comprises the extrastriate cortex. In humans with normal sight, extrastriate cortex is a visual association area, with feature-extracting, shape recognition and multimodal integrating functions; this area is known as peristriate area 19, it refers to a subdivision of the cytoarchitecturally defined occipital region of cerebral cortex. In the human it is located in parts of the lingual gyrus, the cuneus, the lateral occipital gyrus and the superior occipital gyrus of the occipital lobe where it is bounded by the parieto-occipital sulcus, it is bounded on one side by the parastriate area 18. It is bounded rostrally by the angular area 39 and the occipitotemporal area 37. Brodmann area 19-1909 is a subdivision of the cerebral cortex of the guenon defined on the basis of cytoarchitecture, it is cytoarchitecturally homologous to the peristriate area 19 of the human. Distinctive features: Compared to Brodmann area 18-1909, the pyramidal cells of sublayer 3b of the external pyramidal layer are not as densely distributed, the layer is not as narrow, its boundary with the internal granular layer is not as distinct.
Area 19 is a histologically delineated band anterolaterally abutting visual area 18. Single-cell electrophysiological recordings from area 19 in the cat suggest sensitivity to motion-delineated forms. In humans, this band is reputed to contain regions of the visual areas designated V3, V4, V5, V6 in the primate. Functional magnetic resonance imaging shows the existence of various retinotopic maps within area 19. In general, the diverse fields that comprise area 19 have reciprocal connections with areas 17 and 18, as well as posterior parietal and inferior temporal association areas. Area 19 has been noted to receive inputs from the retina via the superior colliculus and pulvinar, may contribute to the phenomenon of blindsight. In patients blind from a young age, the area has been found to be activated by somatosensory stimuli; because of these findings, it is thought that area 19 is the differentiation point of the two visual streams, of the'what' and'where' visual pathways. The dorsal region may contain motion-sensitive neurons, ventral areas may be specialised for object recognition.
Brodmann area List of regions in the human brain Hyvarinen, J. Carlson, Y. and Hyvarinen, L. Early visual deprivation alters modality of neuronal responses in area 19 of monkey cortex, Neurosci. Lett. 26, 239–243 Theories of visual cortex organization in primates: areas of the third level, Prog Brain Res. 1996.
The cerebral cortex known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain, in humans and other mammals. It is separated into two cortices, by the longitudinal fissure that divides the cerebrum into the left and right cerebral hemispheres; the two hemispheres are joined beneath the cortex by the corpus callosum. The cerebral cortex is the largest site of neural integration in the central nervous system, it plays a key role in memory, perception, thought and consciousness. In most mammals, apart from small mammals that have small brains, the cerebral cortex is folded, providing a greater surface area in the confined volume of the cranium. Apart from minimising brain and cranial volume cortical folding is crucial for the wiring of the brain and its functional organisation. In mammals with a small brain there is no folding and the cortex is smooth. A fold or ridge in the cortex is termed a gyrus and a groove is termed a sulcus; these surface convolutions appear during fetal development and continue to mature after birth through the process of gyrification.
In the human brain the majority of the cerebral cortex is not visible from the outside, but buried in the sulci, the insular cortex is hidden. The major sulci and gyri mark the divisions of the cerebrum into the lobes of the brain. There are between 16 billion neurons in the cerebral cortex; these are organised into cortical columns and minicolumns of neurons that make up the layers of the cortex. Most of the cerebral cortex consists of the six-layered neocortex. Cortical areas have specific functions; the cerebral cortex is the outer covering of the surfaces of the cerebral hemispheres and is folded into peaks called gyri, grooves called sulci. In the human brain it is between two and three or four millimetres thick, makes up 40 per cent of the brain's mass. There are between 14 and 16 billion neurons in the cortex, these are organized in cortical columns, minicolumns of the layers of the cortex. About two thirds of the cortical surface is buried in the sulci and the insular cortex is hidden; the cortex is thickest over thinnest at the bottom of a sulcus.
The cerebral cortex is folded in a way that allows a large surface area of neural tissue to fit within the confines of the neurocranium. When unfolded in the human, each hemispheric cortex has a total surface area of about 1.3 square feet. The folding is inward away from the surface of the brain, is present on the medial surface of each hemisphere within the longitudinal fissure. Most mammals have a cerebral cortex, convoluted with the peaks known as gyri and the troughs or grooves known as sulci; some small mammals including some small rodents have smooth cerebral surfaces without gyrification. The larger sulci and gyri mark the divisions of the cortex of the cerebrum into the lobes of the brain. There are four main lobes: the frontal lobe, parietal lobe, temporal lobe, occipital lobe; the insular cortex is included as the insular lobe. The limbic lobe is a rim of cortex on the medial side of each hemisphere and is often included. There are three lobules of the brain described: the paracentral lobule, the superior parietal lobule, the inferior parietal lobule.
For species of mammals, larger brains tend to have thicker cortices. The smallest mammals, such as shrews, have a neocortical thickness of about 0.5 mm. There is an logarithmic relationship between brain weight and cortical thickness. Magnetic resonance imaging of the brain makes it possible to get a measure for the thickness of the human cerebral cortex and relate it to other measures; the thickness of different cortical areas varies but in general, sensory cortex is thinner than motor cortex. One study has found some positive association between the cortical intelligence. Another study has found that the somatosensory cortex is thicker in migraine sufferers, though it is not known if this is the result of migraine attacks or the cause of them. A study using a larger patient population reports no change in the cortical thickness in migraine sufferers. A genetic disorder of the cerebral cortex, whereby decreased folding in certain areas results in a microgyrus, where there are four layers instead of six, is in some instances seen to be related to dyslexia.
The six cortical layers of the neocortex each contain a characteristic distribution of different neurons and their connections with other cortical and subcortical regions. There are direct connections between different cortical areas and indirect connections via the thalamus. One of the clearest examples of cortical layering is the line of Gennari in the primary visual cortex; this is a band of whiter tissue that can be observed with the naked eye in the fundus of the calcarine sulcus of the occipital lobe. The line of Gennari is composed of axons bringing visual information from the thalamus into layer IV of the visual cortex. Staining cross-sections of the cortex to reveal the position of neuronal cell bodies and the intracortical axon tracts allowed neuroanatomists in the early 20th century to produce a detailed description of the laminar structure of the cortex in different species. After the work of Korbinian Brodmann the neurons of the cerebral cortex are grouped into six main layers, from the outer pial surface to the inner white matter.
Layer I is the molecular layer, contains few scattered neurons, including GABAergic rosehip neurons. Layer I consists of extensions of apical dendritic tufts of pyramidal neurons and horiz