Referee Comments: Referee 1

Reviewer 1's Review

“This paper investigates intracerebral stereo-EEG (S-EEG) recording in the hippocampus and neocortex of five epileptic patients in the pre-surgery phase, as compared to the scalp EEG recording, during the first three NREM-REM sleep cycles of the night. The main conclusions are (a) that hippocampal S-EEG power in delta frequencies (1-4 Hz) decreases across sleep cycles and drops during REM sleep periods, indicating homeostatic regulation of delta activity in the hippocampus likewise in neocortical areas; (b) less or no homeostatic effect in the slow oscillations (SO) range, i.e. very low frequencies in the 0.5-1 Hz range, and (c) SO stability across REM - NREM sleep episodes, suggesting a tendency for EEG synchronization of slow wave activity in the hippocampus during REM sleep.

This is an interesting study, clearly and well written, that follows a logical progression and is well supported by the illustrating figures. I have only a few remarks that the authors should address in order to improve their manuscript.

As far as I remember (but I was unable to retrieve the paper to check in details, sorry), the relationship between hippocampal and cortical slow wave activity has been investigated in a Dijk & Wieser paper, I believe using foramen ovale electrodes (Dijk, D.-J. and H.-G. Wieser (1990). Intracranial recording of slow wave activity in man. Sleep '90. J. A. Horne. Bochum, Pontenagel Press: 3-7.) They found parallel variations in SWA in the hippocampus and neocortex I think. Since the present study raises independent variations in SO, it could be interesting to discuss this paper and the potential causes for differences.”

N.B. These are the general comments made by the reviewer when reviewing this paper in light of which the manuscript was revised. Specific points addressed during revision of the paper are not shown.