Role of the medial parieto-occipital cortex in the control of reaching and grasping movements

Abstract

The medial parieto-occipital cortex is a central node in the dorsomedial visual stream. Recent physiological studies in the macaque monkey have demonstrated that the medial parieto-occipital cortex contains two areas, the visual area V6 and the visuomotor area V6A. Area V6 is a retinotopically organized visual area that receives form and motion information directly from V1 and is heavily connected with the other areas of the dorsal visual stream, including V6A. Area V6A is a bimodal visual/somatosensory area that elaborates visual information such as form, motion and space suitable for the control of both reaching and grasping movements. Somatosensory and skeletomotor activities in V6A affect the upper limbs and involve both the transport phase of reaching and grasping movements. Finally, V6A is strongly and reciprocally connected with the dorsal premotor cortex controlling arm movements. The picture emerging from these data is that the medial parieto-occipital cortex is well equipped to control both proximal and distal movements in the online visuomotor guidance of prehension. In agreement with this view, selective V6A lesions in monkey produce misreaching and misgrasping with the arm contralateral to the lesion in visually guided movements. These deficits are similar to those observed in optic ataxia patients and suggest that human and monkey superior parietal lobules are homologous structures, and that optic ataxia syndrome is the result of the lesion of a 'human' area V6A.

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

“…Finally, our results are perfectly consistent with the theory of a dorsomedial visual stream involved in reach‐to‐grasp actions, suggested by Galletti et al. (2003) in nonhuman primates, and well documented by Fattori et al. (2009, 2010).…”

“…These recent findings in humans are consistent with the theory of a dorsomedial visual stream (e.g., V6A) involved in reach‐to‐grasp actions, suggested by Galletti et al. (2003). Indeed, this has been documented by Fattori et al.…”

Neural pathways for cognitive command and control of hand movements

“…These functions are anatomically segregated into specific subregions of the PPC. Medial areas, such as the medial intraparietal area and the "parietal reach region," are engaged by reaching to cued targets in the workspace (21)(22)(23)(24)(25)(26); lateral cortical regions surrounding the intraparietal sulcus (area 5 and the anterior interparietal area) signal the hand postures used to grasp specific objects (27)(28)(29)(30)(31); and areas of the medial wall of the hemisphere integrate arm and hand movements with visual signals (32,33). Motor plans and sensory attention are transformed into action by parietal interconnections with relevant premotor areas of the frontal lobe.…”

Connections of the Dorsomedial Visual Area: Pathways for Early Integration of Dorsal and Ventral Streams in Extrastriate Cortex

“…While the "two streams" model remains a touchstone for the interpretation and integration of clinical, physiological, and anatomical data on visual processing, it continues to evolve. For example, several studies have suggested that the primate dorsal stream is, itself, formed by distinct dorsolateral and dorsomedial circuits, which mediate different aspects of visual behavior (Rosa and Tweedale, 2001;Galletti et al, 2003;Rizzolatti and Matelli, 2003). Perhaps reflecting this dual organization, anatomical studies have demonstrated parallel projections from the primary visual area (V1) to two heavily myelinated, motion-sensitive dorsal areas, which in turn project to the posterior parietal cortex.…”