Dorsomedial area
Encyclopedia
The Dorsomedial area, also known as DM or V6, is a subdivision of the visual cortex
of primates first described by John Allman
and Jon Kaas
in 1975. DM is located in the dorsal part of the extrastriate cortex
, near the deep groove through the centre of the brain (interhemispheric fissure
), and typically also includes portions of the medial cortex, such as the Parieto-occipital sulcus. DM contains a topographically organized representation of the entire field of vision. Like area V5/MT
(middle temporal area), DM receives direct connections from the primary visual cortex. Also similar to MT, DM is also characterized by high myelin
content, a characteristic that is usually present in brain structures involved in fast transmission of information (Rosa et al. 2005).
For many years, it was considered that DM only existed in New World monkeys. However, more recent research has suggested that DM also exists in Old World monkeys and perhaps humans. Another name for DM is "visual area 6" (V6). DM/ V6 is also sometimes referred to as the parietooccipital area (PO), although the correspondence is not exact (Galletti et al. 2005).
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Visual cortex
The visual cortex of the brain is the part of the cerebral cortex responsible for processing visual information. It is located in the occipital lobe, in the back of the brain....
of primates first described by John Allman
John Allman
John Morgan Allman is a neuroscientist at the California Institute of Technology in Pasadena, California and a well recognized expert on primates, cognition and evolutionary neuroscience.-Life:He graduated from University of Chicago, with a PhD....
and Jon Kaas
Jon Kaas
Jon Kaas is a professor at Vanderbilt University and a member of the United States National Academy of Sciences. He has made discoveries about the organization of the mammalian brain, including the description of many areas of the cerebral cortex and their neuroplasticity.Work from the Kaas's...
in 1975. DM is located in the dorsal part of the extrastriate cortex
Extrastriate cortex
The extrastriate cortex is the region of the occipital cortex of the mammalian brain located next to the primary visual cortex, which is also named striate cortex because of its appeareance in the microscope. The extrastriate cortex encompasses multiple functional areas, including V3, V4, V5/MT...
, near the deep groove through the centre of the brain (interhemispheric fissure
Medial longitudinal fissure
The great longitudinal fissure is the deep groove which separates the two hemispheres of the vertebrate brain....
), and typically also includes portions of the medial cortex, such as the Parieto-occipital sulcus. DM contains a topographically organized representation of the entire field of vision. Like area V5/MT
Visual cortex
The visual cortex of the brain is the part of the cerebral cortex responsible for processing visual information. It is located in the occipital lobe, in the back of the brain....
(middle temporal area), DM receives direct connections from the primary visual cortex. Also similar to MT, DM is also characterized by high myelin
Myelin
Myelin is a dielectric material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system. Myelin is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination...
content, a characteristic that is usually present in brain structures involved in fast transmission of information (Rosa et al. 2005).
For many years, it was considered that DM only existed in New World monkeys. However, more recent research has suggested that DM also exists in Old World monkeys and perhaps humans. Another name for DM is "visual area 6" (V6). DM/ V6 is also sometimes referred to as the parietooccipital area (PO), although the correspondence is not exact (Galletti et al. 2005).
Properties
Neurons in area DM/V6 have unique response properties, including an extremely sharp selectivity for the orientation of visual contours, and preference for long, uninterrupted lines covering large parts of the visual field (Baker and collaborators, 1981; Lui and collaborators, 2006). However, in comparison with area MT, a much smaller proportion of DM cells shows selectivity for the direction of motion of visual patterns. Another notable difference is that cells in DM are attuned to low spatial frequency components of an image, and respond poorly to the motion of textured patterns such as a field of random dots. In contrast, cells in MT are often strongly responsive to such stimuli. These response properties suggest that DM and MT may work in parallel, with the former analyzing self-motion relative to the environment, and the latter analyzing the motion of individual objects relative to the background.Pathways
The connections and response properties of cells in DM/ V6 suggest that this area is a key node in a sub-set of the "dorsal stream", referred to by some as the "dorsomedial pathway". This pathway is likely to be important for the control of skeletomotor activity, including postural reactions and reaching movements towards objects (Galletti and collaborators, 2003). The main "feedforward" connection of DM is to the cortex immediately rostral to it, in the interface between the occipital and parietal lobes (V6A). This region has, in turn, relatively direct connections with the regions of the frontal lobe that control arm movements, including the premotor cortexPremotor cortex
The premotor cortex is an area of motor cortex lying within the frontal lobe of the brain. It extends 3 mm anterior to the primary motor cortex, near the Sylvian fissure, before narrowing to approximately 1 mm near the medial longitudinal fissure, which serves as the posterior border for...
.