Extended Data Fig. 3: The hippocampal depth profile during paced oscillations corresponded to the depth profile during endogenous theta oscillations.
From: Precisely timed theta oscillations are selectively required during the encoding phase of memory
(a) Sixteen-site linear silicon probes were chronically implanted in the hippocampus, and LFP recordings were performed in freely moving mice (n = 3 with one mouse excluded from analysis because of inadequate pacing; average pacing efficiency scores: 0.37 for mouse 89, 0.16 for mouse 95, and 0.04 for the excluded mouse 97). Schematic and brightfield histology images of the dorsal hippocampus for mouse 89 and 95. (b) Example raw LFP traces from all 16 recording sites during movement and rest. Ripple amplitude is known to be maximal in the pyramidal cell layer (encircled with red line), and alignment of the probe with the pyramidal layer was performed by visual inspection of sharp wave ripple amplitude and matched with the position of the probe in the histological reconstruction in (a). Scale bar is 250 ms. (c) Average current source density across hippocampal layers from recordings without stimulation (no stimulation) and with rhythmic stimulation at 8, 10, and 12 Hz. Periods from -125 to +125 ms are shown to include approximately two theta cycles (mouse 89, first and second column; mouse 95, third and fourth column). Note that there is a shortening of the theta cycle with higher stimulation frequencies, but during periods with stimulation the most pronounced current source-sink pair remained in slm, which is the termination zone of direct projections from entorhinal cortex. The distribution of less pronounced sink-source pairs across other hippocampal layers is also consistent between stimulation and no stimulation sessions. so, stratum oriens; sp, stratum pyramidale; sr, stratum radiatum; slm, stratum lacunosum moleculare.
