Abstract
Reaching and manipulative actions allow human and non-human primates to interact with the surrounding world. The execution of foveated reaching movements requires the combination of visual and motor skills, allowing the arm to be guided and kept in place by several kinds of information (eye position, proprioceptive, visual). Several areas of the superior parietal lobule (SPL) are involved in the progressive integration of information related to the current position of the eyes and proprioceptive signals from the arm occurring during and after reaching movements. In this study we assessed the relative influence of eye-position and somatosensory signals during static arm positions at the end of a 3D fixation-to-reach task in three SPL areas: V6A, located in the anterior bank of the parieto-occipital sulcus, PEc, bordering anteriorly to V6A, and PE, located more rostrally in the SPL. We analyzed single cell discharges recorded from areas V6A (N= 303), PEc (N= 264) and PE (N= 189) of two Macaca fascicularis in two main time intervals: i) target fixation and ii) holding of the foveated target. We found that the three areas were differently modulated by eye-position and proprioceptive signals, being PE cells more involved in the encoding of limb postures while V6A and PEc neurons more involved in the processing of eye-position information during target fixation. Our results support the existence of a functional antero-posterior trend along the SPL: from area PE, strongly dominated by proprioceptive signals of the arm holding the target, to the most functionally heterogenous areas PEc and V6A, which showed an additional gaze influence. This coding scheme parallels the increase of somatosensory and the simultaneous decrease of visual processing observed along the caudo-rostral axis of the SPL.