Arm movement-related neurons in the visual area V6A of the macaque superior parietal lobule.

Area V6A is a cortical visual area located in the posterior face of the superior parietal lobule in the macaque monkey. It contains visual neurons as well as neurons not activated by any kind of visual stimulation. The aim of this study was to look for possible features able to activate these latter neurons. We tested 70 non-visual V6A neurons. Forty-three of them showed an arm movement-related neural discharge due to somatosensory stimulation and/or skeletomotor activity of the upper limbs of the animal. The arm movement-related neural discharge started before the onset of arm movement, often before the earliest electromyographic activity. Thus, although the discharge is probably supported by proprioceptive and tactile inputs it is not fully dependent on them. Arm movement-related neurons of area V6A seem to be well equipped for integrating motor signals related to arm movements with somatosensory signals evoked by those movements. Taking into account also the visual characteristics of V6A neurons, it seems likely that area V6A as a whole is involved in the visual guiding of reaching.