Overlapping representations for reach depth and direction in caudal superior parietal lobule of macaques

Abstract

-Reaching movements in the real world have typically a direction and a depth component. Despite numerous behavioral studies, there is no consensus on whether reach coordinates are processed in separate or common visuomotor channels. Furthermore, the neural substrates of reach depth in parietal cortex have been ignored in most neurophysiological studies. In the medial posterior parietal area V6A, we recently demonstrated the strong presence of depth signals and the extensive convergence of depth and direction information on single neurons during all phases of a fixate-to-reach task in 3-dimensional (3D) space. Using the same task, in the present work we examined the processing of direction and depth information in area PEc of the caudal superior parietal lobule (SPL) in three Macaca fascicularis monkeys. Across the task, depth and direction had a similar, high incidence of modulatory effect. The effect of direction was stronger than depth during the initial fixation period. As the task progressed toward arm movement execution, depth tuning became more prominent than directional tuning and the number of cells modulated by both depth and direction increased significantly. Neurons tuned by depth showed a small bias for far peripersonal space. Cells with directional modulations were more frequently tuned toward contralateral spatial locations, but ipsilateral space was also represented. These findings, combined with results from neighboring areas V6A and PE, support a rostral-to-caudal gradient of overlapping representations for reach depth and direction in SPL. These findings also support a progressive change from visuospatial (vergence angle) to somatomotor representations of 3D space in SPL.

Directional tuning for eye and arm movements in overlapping regions in human posterior parietal cortex

“…Here, we have found that more anterior regions in the parietal cortex corresponding to SPLp and, at lower thresholds, SPLa and SPLr contained neural populations tuned to eye movement direction. These findings are in line with previous studies that found that neurons in medial posterior parietal cortex in the monkey are modulated by both eye direction and depth (Hadjidimitrakis et al, 2015;Breveglieri et al, 2012). Our findings suggest that these areas are not only coarsely sensitive to the difference between eye movements performed towards the left or right, but that the underlying neural populations show properties that are compatible with directional tuning.…”

Posterior parietal cortex estimates the relationship between object and body location during locomotion

“…This suggests that these cells are tuned to respond to objects only when they are within a limited range of DTC or TTC. A similar tuning of cell responses to distance in response to looming stimuli is found in the ventral intraparietal area (VIP) of the PPC in non-human primates ( Colby et al, 1993 ; Graziano and Cooke, 2006 ; see also Hadjidimitrakis et al, 2015 ), as well as in the premotor cortex (PMC, Graziano et al, 1997 ). Graziano ( Graziano and Cooke, 2006 ) has proposed that such cells may play a role in defensive and avoidance behavior.…”

Claustral afferents of superior parietal areas PEc and PE in the macaque

“…This area contains an incomplete representation of the body, mainly focused on upper and lower limbs, without an evident topographic organization (Breveglieri et al, 2006(Breveglieri et al, , 2008. It has been recently demonstrated that a large percentage of PEc neurons encodes both direction and depth information during arm reaching movements (Hadjidimitrakis et al, 2015), and contributes to hand-target transformations for reaching (Piserchia et al, 2016). In contrast, area PE (which has been traditionally equated to Brodmann's area 5) contains an almost complete representation of the body, with a coarse topographic organization (Taoka et al, 1998(Taoka et al, , 2000Padberg et al, 2007).…”