Fig. 11.

Changes in activity characteristics of neurons that had one PEF during both simple and ladder locomotion but were active in different phases of the stride (group III neurons). A: comparison of preferred phases of activity in individual neurons during simple and ladder locomotion. The x-axis and y-axis of each point show the preferred phase of a neuron during simple and ladder locomotion, respectively. Neurons whose characteristics were statistically significantly different during the two tasks are shown with filled circles; the others are shown with open circles. Areas that correspond to the swing phase during one task but stance phase during the other task are shaded. B: negative correlation between the change in the depth of modulation and the duration of PEF. The x-axis and y-axis of each point show the difference in a discharge characteristic of a neuron between simple and ladder locomotion. The difference is positive if the value of the parameter was larger during ladder locomotion. Only neurons with statistically significant differences in the depth of modulation between two tasks are shown. The coefficient of correlation (r) is indicated. C: schematic presentation of the most frequently observed type of the change in the discharge pattern of group III neurons upon transition from simple to ladder locomotion: the shift in the preferred phase occurs because the activity in a part of the PEF observed during simple locomotion decreases during ladder locomotion. Solid line shows the activity during simple locomotion; interrupted line shows the activity during ladder task. Vertical dashed line shows the transition between swing and stance. D: example of activity of a typical group III neuron. Area histogram shows the activity of the neuron during simple locomotion. Bar histogram shows its activity during ladder task. To promote visualization of the difference between activities in two tasks, the cycle is repeated twice. E and F: same as C and D but showing the second most frequent type of the activity change in group III neurons when the shift in the preferred phase occurs because the activity in a part of the PEF observed during simple locomotion decreases during ladder locomotion, and this reduction is accompanied by an increase in the discharge rate during the remaining part of the PEF.