Abstract
The superior parietal lobule (SPL) is strongly involved in organizing arm actions in space. Despite neuropsychological studies reported that patients with SPL lesions show deficits in reaching targets in depth, so far only few single cell recording studies addressed this issue. Cortical area V6A, located in the SPL of primates, carries signals related to the distance of targets from the eyes, and contains neurons with arm movement-related activity. Recent neurophysiological studies show that area V6A integrates, often at single cell level, vergence with gaze direction signals, thus encoding spatial location in 3D space (Hadjidimitrakis et al., Plos One 2011). The aim of present study was to examine the spatial encoding of single V6A neurons during fixation, preparation, and execution of reaches towards foveated visual targets in depth. Single unit activity was recorded in two macaque monkeys performing a visually-guided reaching task in darkness. Animals were required to fixate and reach targets (LEDs) placed at different positions and depth in 3D space. In the majority of cells, a significant effect of both target direction and depth was found in all time epochs. Spatial modulations were generally maintained from fixation through subsequent task epochs, till reaching execution. Spatial encoding was remarkably consistent across epochs, with common preferences evenly distributed in 3D space. Given the functional properties of V6A neurons, we suggest that this spatial information is integrated with somatosensory input coming from the upper limbs, to define and control the part of space that can be reached by the hands. These new findings demonstrate that, in an area involved in reaching and grasping (Fattori et al., Eur. J. Neurosci 2005; Fattori et al., J. Neurosci 2010), the encoding of action in 3D space is accomplished through the interaction of a variety of signals.
Meeting abstract presented at VSS 2012