Figure 9. Post-stimulus resumption of cortical persistent firing dictates the dynamics of MSN late response to cortical stimulation.

A, to examine the phase shifting effect of cortical stimulation in the slow wave condition (n = 8, 4 s inter-stimulus interval, 25–100 trials per neuron), we computed inter-trial instantaneous phase (IIP) distributions for the simultaneously recorded ECoG, MUras and MSN V_m, and took circular dispersion of IIP distributions as a measure of stimulus-induced phase concentration. IIP circular dispersion fell dramatically following stimulation in all three recordings (*P < 0.001 versus pre-stimulus, t test for paired data). B, polar plots illustrating the latencies to the first post-stimulus persistent cortical firing episode (B1) or to the MSN LD (B2) as a function of ECoG phase at stimulus arrival (n = 8 MUras–MSN pairs, 4 s inter-stimulus interval). The latency to cortical ensemble activation was computed from wavelet decomposed and normalized MUras, as the time to the first negative-to-positive post-stimulus waveform transition. Polar plot data are summarized in the box and whisker graphs below, showing median latency (red bar), 25–75% data interval (box) and range (error bar) for the four quadrants (A, B, C and D) of the corresponding polar plots. Grey lines are MUras waveform (B3) or MSN membrane potential (B4) mean relative amplitudes as a function of ECoG IP at the time of stimulus arrival (upper x-axis) (P < 0.00001, Kruskall-Wallis ANOVA; *P < 0.05 versus quadrants C and D, post hoc Tukey test). C, latency of MSN LD plotted as a function of the latency of cortical ensemble activation in slow wave (n = 8 MUras–ECoG pairs, black circles) and activated ECoG conditions (n = 4 MUras–ECoG pairs, red circles). LD latency increased linearly with increasing cortical ensemble activation delay (r = 0.81, P < 0.001 for the regression's ANOVA). One MUras–MSN pair could be recorded in the activated ECoG condition only.