Phase-locking of spontaneous and tone-elicited pontine waves to hippocampal theta waves during REM sleep in rats

Temporal relationships between hippocampal theta waves and pontine waves (P waves) during rapid-eye-movement (REM) sleep were investigated in rats. P waves were phase-locked to the positive theta peak. The phase relationships of P waves elicited by a tone stimulus (PE waves) to hippocampal theta waves were also analyzed to qualitatively clarify the mechanism of phase-locking between these two phenomena. PE waves occurred at the positive theta peak, as seen for spontaneous P waves. This phase preference of PE waves could be understood as that of the response probability to tone stimulus. These data suggest that the P-wave generator receives inputs that mimic theta waves. As hippocampal theta waves and P waves are known to be involved in learning and memory processes during REM sleep, the present studies could help to clarify these functions.