Two premotor areas (6aα and 6aγ) involved in motor preparation and execution during visually guided locomotion in the cat.

We examined the contribution of areas 6aα and 6aγ of the cat pericruciate cortex to the control of visually guided locomotion by recording single unit activity from layer V of the cortex while cats stepped over obstacles attached to a moving belt. We found populations of neurons in both areas (53% in area 6aα; 25% in area 6aγ) that modified their discharge activity in advance of and/or during the steps over the obstacle. In both areas we found some cells that modified their activity only when the contralateral or ipsilateral limb was the first to step over the obstacle and others that discharged regardless of which limb was the first to step over. Retrograde tracer injections into each area showed differential projections from the primary motor cortex (area 4γ), with area 6aα receiving inputs from rostromedial 4γ (controlling more proximal movements) and 6aγ receiving inputs from more rostrolateral (controlling more distal movements) regions of 4γ. Area 6aα, in addition, received inputs from area 6iffu. Both regions received inputs from area 5 of the posterior parietal cortex. The results support a role for each area in the planning and execution of visually guided gait modifications.