Fig. 6.

Population characteristics of one-period of elevated firing (PEF) neurons. A and B and G and H: example of activity of a typical neuron (group I neuron, see Fig. 13) during walking on the flat surface (A, B) and along the horizontal ladder (G, H). The activity is presented as a raster of 50 step cycles (A, G) and a histogram (B, H). In the rasters, the duration of strides is normalized to 100%, and the rasters are rank ordered according to the duration of the swing phase. The end of swing and the beginning of the stance in each cycle is indicated by an open triangle. In histograms, the horizontal interrupted line indicates the average discharge frequency during standing. The horizontal black bar shows the PEF, and the circle indicates the preferred phase (as defined in methods). C and I: distribution of preferred phases of activity of all one-PEF neurons during simple (C) and ladder (I) locomotion. D and J: proportion of active neurons (neurons in their PEF) in different phases of the step cycle during simple (D) and ladder (J) locomotion. E and K: mean discharge rate of neurons during simple (E) and ladder (K) locomotion. Thin lines show SE. F and L: phase distribution of PEFs during simple (F) and ladder (L) locomotion. Each horizontal bar represents the PEF location of 1 neuron (shown in black in 1 cycle only) relative to the step cycle. Neurons are rank ordered so that those active earlier in the cycle are plotted at top of graph. Vertical solid lines highlight 1 cycle. Vertical interrupted lines denote end of swing and beginning of stance phase.