Foveal and peripheral reaching activity in the macaque cortical area V6A

Abstract

In a previous work, we demonstrated a spatial tuning for reaching activity in the majority of V6A cells, suggesting that V6A reach-related neurons could be able to code the direction of movement of the arm and the position of the hand/arm in space (Fattori et al, 2005, Eur. J. Neurosci). In that work, the animals reached foveated targets placed in different spatial locations. As V6A neurons are strongly modulated by the direction of gaze (Galletti et al., 1995, EurJ Neurosci), it could be that the above described spatial tuning of reaching activity is due to a gaze modulation of neural activity. Thus, we here study the coding of directions of reach with a constant-gaze task. The monkey reached central or peripheral locations while looking constantly towards a central fixation point. The task was performed in complete darkness except for the very small and barely visible fixation point. The monkey always started the reaching movement with the hand near the chest, then reached and held the target location in peripersonal space, and finally went back to the home button. We tested 101 V6A neurons from 1 monkey with this constant-gaze reaching task. We found that 65% of them showed a neural modulation during the execution of reaching movements towards foveal and peripheral targets. Some of them showed activities preferring the reaching movement to the foveated target, others to the ipsilateral, and others to the contralateral one. A similar percentage of neurons (60%) was modulated during hand holding among different spatial locations, again with the gaze fixed in the straight ahead direction. We suggest that the visuomotor area V6A plays a key role in the fronto-parietal loops monitoring and/or controlling goal-directed voluntary arm movements both towards foveated and peripheral ones.