title: The parietal reach region is limb specific and not involved in eye-hand coordination.
abstract: Primates frequently reach toward visual targets. Neurons in early visual areas respond to stimuli in the contralateral visual hemifield and without regard to which limb will be used to reach toward that target. In contrast, neurons in motor areas typically respond when reaches are performed using the contralateral limb and with minimal regard to the visuospatial location of the target. The parietal reach region (PRR) is located early in the visuomotor processing hierarchy. PRR neurons are significantly modulated when targets for either limb or eye movement appear, similar to early sensory areas; however, they respond to targets in either visual field, similar to motor areas. The activity could reflect the subject's attentional locus, movement of a specific effector, or a related function, such as coordinating eye-arm movements. To examine the role of PRR in the visuomotor pathway, we reversibly inactivated PRR. Inactivation effects were specific to contralateral limb movements, leaving ipsilateral limb and saccadic movements intact. Neither visual hemifield bias nor visual attention deficits were observed. Thus our results are consistent with a motoric rather than visual organization in PRR, despite its early location in the visuomotor pathway. We found no effects on the temporal coupling of coordinated saccades and reaches, suggesting that this mechanism lies downstream of PRR. In sum, this study clarifies the role of PRR in the visuomotor hierarchy: despite its early position, it is a limb-specific area influencing reach planning and is positioned upstream from an active eye-hand coordination-coupling mechanism.
authors.affiliation: Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Yttri
authors.forename: Cunguo
authors.initials: C
authors.lastname: Wang
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Liu
authors.forename: Lawrence H
authors.initials: LH
authors.lastname: Snyder
mesh_terms: D000818:Animals; D001288:Attention; D006225:Hand / Q000294:innervation / Q000502:physiology*; D008253:Macaca mulatta; D008297:Male; D010296:Parietal Lobe / Q000502:physiology*; D011597:Psychomotor Performance; D012438:Saccades
keywords: eye-hand coordination; parietal reach region; reaching; visuomotor