'Arm-reaching' neurons in the parietal area V6A of the macaque monkey

In previous experiments we have found that several cells of area V6A in the macaque superior parietal lobule were activated by small and stereotyped m ovements of the arms (C. Galletti, P. Fattori, D. F. Kutz & P. P. Battaglin i, Eur J. Neurosci., 1997, 9, 410). This behaviour was not accounted for by retinal information, nor by somatosensory inputs from the arms. We now wan t to investigate whether V6A neurons are modulated by purposeful movements aimed at reaching visual targets or targets located outside the field of vi ew. V6A neuronal activity was collected while monkeys performed arm movemen ts during an instructed-delay reaching task in darkness. The task required the animal to reach out for a visual target in the peripersonal space and t o bring the hand back to its body. Quantitative analysis of neuronal activi ty carried out on 55 V6A neurons showed that: (i) the great majority of neu rons (71%) was significantly modulated during the execution of arm movement s; (ii) 30% of neurons were significantly modulated during preparation of r eaching; and (iii) modulations during both execution and preparation of rea ching occurred in the absence of any visual feedback and were not due to ey e movements. V6A reach-related neurons could be useful in guiding the hand to reach its target with or without visual feedback.