A secondary motor area contributing to interlimb coordination during visually guided locomotion in the cat

We investigated the contribution of cytoarchitectonic cortical area 4 delta c, in the caudal bank of the cruciate sulcus of the cat, to the control of visually guided locomotion. To do so, we recorded the activity of 114 neurons in 4 delta c while cats walked on a treadmill and stepped over an obstacle that advanced toward them. A total of 84/114 (74%) cells were task-related and 68/84 (81%) of these cells showed significant modulation of their discharge frequency when the contralateral limbs were the first to step over the obstacle. These latter cells included a substantial proportion (27/68 40%) that discharged between the passage of the contralateral forelimb and the contralateral hindlimb over the obstacle, suggesting a contribution of this area to interlimb coordination. We further compared the discharge in area 4 delta c with the activity patterns of cells in the rostral division of the same cytoarchitectonic area (4 delta r), which has been suggested to be a separate functional region. Despite some differences in the patterns of activity in the 2 subdivisions, we suggest that activity in each is compatible with a contribution to interlimb coordination and that they should be considered as a single functional area that contributes to both forelimb-forelimb and forelimb-hindlimb coordination.