Cortical Connections of Area V6Av in the Macaque: A Visual-Input Node to the Eye/Hand Coordination System

Abstract

The goal of the present study was to elucidate the corticocortical afferent connections of area V6Av, the ventral subregion of area V6A, using retrograde neuronal tracers combined with physiological and cytoarchitectonic analyses in the macaque monkey. The results revealed that V6Av receives many of its afferents from extrastriate area V6, and from regions of areas V2, V3, and V4 subserving peripheral vision. Additional extrastriate visual projections originate in dorsal stream areas MT and MST. Area V6Av does not receive projections directly from V1; such connections were only observed when the injection sites crossed into area V6. The strongest parietal lobe afferents originate in fields V6Ad, PGm, MIP (medial intraparaietal), and PG, with frontal lobe afferents originating from the frontal eye field, caudal area 46, and the rostral subdivision of the dorsal premotor area (F7). A comparison of their respective connections supports the view that V6Av is functionally distinct from adjacent areas (V6 and V6Ad). The strong afferents from V6 and other extrastriate areas are consistent with physiological data that suggest that V6Av is primarily a visual area, supporting the notion that V6Av is part of a dorsomedial cortical network performing fast form and motion analyses needed for the visual guidance of action.

Eye Position Encoding in Three-Dimensional Space: Integration of Version and Vergence Signals in the Medial Posterior Parietal Cortex

“…Modulations of neural activity by fixation depth have been also found in the VIP (ventral intraparietal) area (Colby et al, 1993) and in visual areas V2 and V4 (Dobbins et al, 1998;Rosenbluth and Allman, 2002), all directly connected with V6A. The two extrastriate areas, in particular, send strong inputs to the ventral part of V6A, which in turn is strongly connected with the dorsal part of V6A (Passarelli et al, 2011), so they are likely candidates to provide depthrelated signals to V6A. Finally, vergence related modulations have been also observed in the primary visual cortex (Trotter et al, 1996) and could be disynaptically transmitted to V6A through area V6 ).…”

“…It receives input from the posterior parietal areas LIP and PG (Gamberini et al, 2009), where vergence angle has been reported to have an effect on presaccadic and fixation activities, respectively (Sakata et al, 1980;Genovesio and Ferraina, 2004). Also the area MIP is strongly and reciprocally connected with V6A (Gamberini et al, 2009;Passarelli et al, 2011), and it is known that MIP (also named PRR) hosts neurons with planning activity for reaching modulated by fixation depth (Bhattacharyya et al, 2009) et al, 2011). Modulations of neural activity by fixation depth have been also found in the VIP (ventral intraparietal) area (Colby et al, 1993) and in visual areas V2 and V4 (Dobbins et al, 1998;Rosenbluth and Allman, 2002), all directly connected with V6A.…”

“…The present work was designed to test whether eye version and vergence modulate neuronal activity in V6A, a cortical area located in the medial part of monkey PPC (Galletti et al, 1996(Galletti et al, , 1999a. V6A is strongly connected with PPC areas that encode eye movements and fixations in depth, like the lateral intraparietal area (LIP) and area 7a (Gamberini et al, 2009;Passarelli et al, 2011). It also contains neurons modulated by arm-reaching movements in 3D space Marzocchi et al, 2008;Bosco et al, 2010), and by gaze position in a frontoparallel plane (Galletti et al, 1995;Nakamura et al, 1999).…”

Vision for Action in the Macaque Medial Posterior Parietal Cortex

“…It is now well established that the dorsal visual stream processes vision for action (Goodale and Milner, 1992;Milner and Goodale, 1995), and the dorsomedial pathway has been recently shown to be involved in the encoding of all phases of prehension Gamberini et al, 2009;Passarelli et al, 2011). Indeed, one of the areas of the dorsomedial pathway, the medial posteriorparietal area V6A, hosts neurons encoding the direction of arm reaching movements , neurons modulated by the orientation of the hand in reach-to-grasp movements , and neurons encoding the type of grip required to grasp objects of different shapes .…”

“…Area V6A receives visual information from area V6 Gamberini et al, 2009;Passarelli et al, 2011), a retinotopically organized extrastriate area of the medial parietooccipital cortex (Galletti et al, 1999b), and from other visual areas of the posterior parietal cortex (Gamberini et al, 2009;Passarelli et al, 2011). It has been reported that area V6A contains visual neurons that are very sensitive to the orientation of visual stimuli (Galletti et al, 1996(Galletti et al, , 1999aGamberini et al, 2011), thus providing critical information for object grasping .…”