Figure 9. Stimulus strength has only a minor impact on complex spike responsiveness.

A, movements of all large facial whiskers were performed using a piezo‐actuator at three different speeds (weak: 1 mm displacement in 62 ms; moderate: 2 mm displacement in 31 ms; strong: 4 mm displacement in 16 ms). The stimulus sequence was randomly permuted. The recordings were made in awake mice. B, field of view with 24 identified and colour‐coded Purkinje cells (left) and their corresponding fluorescence traces (right). Stimuli were presented every 2 s and in between trials the laser illumination was briefly blocked to avoid photobleaching. Note that the periods without laser illumination are not drawn to scale. The vertical shaded areas indicate stimulus duration (which was inverse with the stimulus strength). C, summed fluorescence trace composed of all 24 individual traces showing that not all trials evoked ensemble‐wide responses. Some spontaneous, inter‐trial activity was also observed. D, median number of complex spikes per frame (of 40 ms) per trial (shaded areas: interquartile ranges) for the three stimulus strengths show little difference for the weak and moderate stimulation. The time course and amplitude (1–4 mm) of the three stimuli is shown schematically at the bottom of the graph. Strong stimulation elicited about 30% more complex spikes, as evident from the peak responses for each stimulus intensity. E, box plots showing the response strength for the 209 significantly responsive Purkinje cells (out of 340 Purkinje cells that were measured in this way). F, response rates for all Purkinje cells that showed an increase in response rate with increased stimulus intensity. Only a few cells stand out in that they show a strong response that consistently increases with stimulus strength (lines on top). G, the same for the Purkinje cells that showed a decrease in response strength with increasing stimulus intensity. H, histogram of the differences in peak responses between the strong and the weak stimuli of all 340 recorded Purkinje cells. W = weak; M = moderate; S = Strong; ^*** P < 0.001 (Friedman's test).