Dorsomedial area

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 parietooccipital 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).

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 cortex.