The involvement of monkey premotor cortex neurones in preparation of visually cued arm movements.

Some neurones in macaque postarcuate premotor area modulate their firing frequency in relation to motor tasks which require visual information. We previously reported that a large proportion of these neurones modulate during execution of a detour reaching task in which the movement phase was separated in time from the phase in which the monkey received a visual cue for the movement required to retrieve a food reward. A large proportion of task-related neurones (75%) modulated during this 'visual' phase, in which no task-related movements were made. This modulation was related to the position of the food reward, which served as the visual cue. Most of these neurones were located in cortical area 6, close to the arcuate curvature and its spur, but also more caudally in area 4 and rostrally in area 8. In the present chronic recording experiments in monkeys, several variations of the original task were used in order to test whether the 'visual'-related neuronal modulation could be involved in preparation of the upcoming movement. This modulation is unlikely to be related to any eye or arm movements occurring during the visual phase or to changes in environmental illumination. Neither can it be related to the presence of the visual cue in a particular part of the visual field, since the pattern of neuronal modulation was similar when a cue with a fixed position was used. This modulation was, however, contingent upon the occurrence of food retrieval during the subsequent 'movement phase', since it was abolished or diminished during presentation of a 'food-reward' which the monkey did not retrieve. For several neurones, modulation pattern during the visual phase depended on whether the food reward was to be retrieved with a gross hand movement or with relatively independent finger movements. It is likely, therefore, that neurones in the postarcuate premotor cortex are involved in preparation for arm movements with the help of visual cues. The results are discussed in view of corticocortical pathways which might be involved in transmission of visual information from visual areas through parietal association areas and premotor cortex to the primary motor cortex.