Fig. 5.

Cell activity in the ipsilateral lead condition. A, B) Two examples of limb-independent cells. Ai and Bi illustrate the cell discharge activity of 2 cells, each triggered on the onset of activity in the coClB muscle during both the contralateral (red traces) and ipsilateral (green traces) lead conditions. Aii, Bii: Activity in the same 2 cells is now triggered on the activity of the lead ClB (i.e. the period of activity in the first limb to step over the obstacle). These 2 cells are indicated by “5A,B” in Fig. 3. Arrows in Fig. 5Bii indicate the period of activity of the coSrt in the co- and iLead conditions. C, D: Two cells that showed significant modification of activity only in the ipsilateral lead condition. Ci, Di: The activity of the cells is illustrated triggered on the activity of the coClB in both coLead and iLead conditions. The numbers beside the periods of EMG activity indicate the sequence of activation of each muscle as each limb in turn steps over the obstacle. Numbers are color-coded in the same way as for the traces. Only the sequence of activity during the iLead condition is illustrated in Di. Cii) The activity of the cell illustrated in Ci is now synchronized to the onset of activity in the iSrt muscle as the ipsilateral hindlimb passes over the obstacle. Dii) The activity of the cell in Di is synchronized to the onset of activity in the coSrt as the contralateral hindlimb passes over the obstacle in the iLead condition. B1 and B2 indicate the same 2 bursts of activity in Di and Dii, displaced because of the difference in the burst used to trigger the display. The EMG burst #4 corresponds to that in Di (green traces). Bars under the histograms indicate the periods of significant modified activity. Figure otherwise arranged as in Fig. 2.