Fig. 6.

Pro-arousal slow firing follows local theta oscillations in MSvDB. A: schematics of the Z-shift method. Blue trace indicates LFP; black and red rasters represent original and time-shifted neuronal spikes, respectively. Phase-locking Z values were calculated while shifting neuronal spikes relative to LFP signals. Positive shift in time, if resulting in a larger Z value, suggests that the neuronal spikes are better phase-locked to LFP signals in the future. B: an example of Z values from 1 pro-arousal slow-firing neuron, calculated for theta oscillations for both WK and REM episodes concatenated together. HP_LFP, LFP theta oscillations in the hippocampus; MS_LFP, LFP theta oscillations in MSvDB. The maximal Z value for phase-locking to theta oscillations in MSvDB occurred before 0, suggesting that the neurons spikes followed the theta oscillations in MSvDB LFP in the past. C: histogram of time-shift distribution corresponding to maximal Z values of significantly phase-locked (P < 0.01) MSvDB neurons during WK, REM sleep, or both states. Positive spike shift suggests spike leading LFP theta oscillation, and vice versa. Pro-arousal slow-firing neurons mostly follow LFP theta oscillations in MSvDB, whereas fast-firing neurons mostly lead theta oscillations in both the hippocampus and MSvDB.