Figure 5. OFF periods affect cortical responsiveness.

(A) An average profile of neuronal spiking of two individual neurons from the frontal (left) and from the parietal (right) cortex during a double-pulse electrical stimulation (interpulse interval 50 ms). Note a slightly larger response to the 2nd pulse in the frontal neuron and a substantial increase in firing after the 2nd pulse of the parietal neuron. Insets – corresponding waveshape of the extracellular action potentials (mean± std.dev.) (B) Average neuronal activity in the frontal cortex triggered by spontaneous OFF periods (mean, n = 9 rats). (C) Left. An increase in neuronal firing rates in the first 20 ms after the electrical pulse relative to the mean firing rates in the 2 sec before the stimulus for the trials with low and high incidence of spontaneous OFF periods during preceding 2 sec. Mean ratio ± SEM, n=9 rats. Right. Mean values of the synchrony (1/variability) between individual neurons in the initial response to the electrical pulse computed for the trials with low and high incidence of spontaneous OFF periods during preceding 2 sec. Mean values ± SEM, n=9 rats are shown as % of the mean. (D) Left. The relationship between the incidence of spontaneous OFF periods in the 2 sec interval before the electrical pulse and firing rates in the first 10 ms after the pulse on the control day (after 4 hours of undisturbed waking and sleep). All trials for each rat are subdivided in ten 10% percentiles as a function of the number of OFF periods and corresponding evoked firing rates are computed for each percentile. Mean values + SEM, n=9 rats. Right. The same as left panel computed for evoked firing rates after 4 hour continuous wakefulness (W4).