The Dorsomedial Pathway Is Not Just for Reaching: Grasping Neurons in the Medial Parieto-Occipital Cortex of the Macaque Monkey

Abstract

Brain control of prehension is thought to rely on two specific brain circuits: a dorsomedial one (involving the areas of the superior parietal lobule and the dorsal premotor cortex) involved in the transport of the hand toward the object and a dorsolateral one (involving the inferior parietal lobule and the ventral premotor cortex) dealing with the preshaping of the hand according to the features of the object. The present study aimed at testing whether a pivotal component of the dorsomedial pathway (area V6A) is involved also in hand preshaping and grip formation to grasp objects of different shapes.Two macaque monkeys were trained to reach and grasp different objects. For each object, animals used a different grip: whole-hand prehension, finger prehension, hook grip, primitive precision grip, and advanced precision grip. Almost half of 235 neurons recorded from V6A displayed selectivity for a grip or a group of grips. Several experimental controls were used to ensure that neural modulation was attributable to grip only.Thesefindings,inconcertwithpreviousstudiesdemonstratingthatV6Aneuronsaremodulatedbyreachdirectionandwristorientation,that lesion of V6A evokes reaching and grasping deficits, and that dorsal premotor cortex contains both reaching and grasping neurons, indicate that the dorsomedial parieto-frontal circuit may play a central role in all phases of reach-to-grasp action. Our data suggest new directions for the modeling of prehension movements and testable predictions for new brain imaging and neuropsychological experiments.

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

“…We have found that ϳ50% of V6A neurons are modulated by gaze direction and depth of fixation when monkeys perform saccades and fixate targets at different locations, in peripersonal as well as in extrapersonal space. We have found responses that in most cases were higher for fixating targets located within the reaching distance, thus supporting the proposed role of V6A in monitoring reach-to-grasp actions (Galletti et al, 2003;Fattori et al, 2009Fattori et al, , 2010Hadjidimitrakis et al, 2011).…”

Probing the reaching–grasping network in humans through multivoxel pattern decoding

“…Finally, our results provided further evidence against the hypothesis of a clear‐cut distinction between a dorsomedial (e.g., SPOC, medial intraparietal area MIP, and PMd) and dorsolateral (e.g., hAIP and PMv) pathways, specialized for reaching‐only and reach‐to‐grasp actions, respectively, as reported in a series of recent studies on human and nonhuman primates (Fattori et al. 2009, 2010; Cavina‐Pratesi et al. 2010; Monaco et al.…”

“…(2003) in nonhuman primates, and well documented by Fattori et al. (2009, 2010). Reaching‐only and reach‐to‐grasp actions could be better characterized by temporal, rather than spatial criteria across planning and execution stages of the action, as also suggested by a recent study of Begliomini et al.…”

“…(2009) and more directly by Fattori et al. (2010), who showed evidence of grasping neurons in the medial parieto‐occipital cortex of the macaque monkeys. The abovementioned results about macaque area V6A suggested SPOC area as its putative homolog in humans (Pitzalis et al.…”

Reaching Activity in the Medial Posterior Parietal Cortex of Monkeys Is Modulated by Visual Feedback

“…V6A is a parietal area receiving visual information (Galletti et al, 1996;1999;Gamberini et al, 2009) as well as somatosensory-and movement-related signals relative to reach and grasp actions (Galletti et al, 1997;Fattori et al, 2001;Breveglieri et al, 2002;Fattori et al, 2005;Fattori et al, 2009;Fattori et al, 2010). The present study was designed to determine whether and how the vision of the moving limb influences the activity of V6A neurons during reaching movements.…”