Figure 1.

A, Coronal MR and CT images of hippocampal electrode trajectories. CT image of tract (top) coregistered and superimposed on MR image (middle) shows the electrode tip (white puff) registered to CA3/DG of hippocampus for m3 (indicated in B), closely matching the MR with tracts seen for m1 (bottom). Top, Right, Location of the recording chamber on the skull for m4, with electrode grid locations (white vertical tracts). The reconstructed electrode trajectory (green) and tip locations (red) reveal the hippocampal recording sites, primarily in CA3/DG. B, Schematic drawings of coronal sections of the hippocampal formation. Red dots, Recording locations; #, CA3; *, CA1; ^, dentate gyrus. Illustrations adapted from Saleem and Logothetis (2012). C, Spike scatter plots from recordings on one tetrode based on energy (same tetrode and session as in D and E). D, Examples of the average waveforms of units isolated from one tetrode, during the same session in which SWRs were recorded (shown in E). Waveforms are shown inverted, by convention. E, Broadband traces of SWR events from m1. Tetrode 7 was used for SWR detection in this session; the simultaneously recorded activity on Tetrode 5 is shown on the corresponding row. SWRs were observed in a limited range of depth across the chronically implanted tetrodes, where units were also observed (C, D). F, Illustration of the ripple envelope threshold method calculated for a single session and applied to an example segment of signal containing two SWRs. Shown in black is an example segment of the recorded signal that contains two ripples. The filtered signal envelope (final detection step) is shown in gray. An envelope z-score of 3 (original signal) is shown by a blue horizontal line, and the change in this threshold after simulating a 500% increase in SWR events is shown in green (see Materials and Methods), revealing the tolerance of the threshold method to large changes in ripple rates.