Figure 5.
High-frequency oscillations in the parahippocampal cortex and hippocampus. A, Detection times and mean frequencies of high-frequency oscillations (gamma, ripples, and FR) between 40 and 600 Hz (three individual channels are depicted by different colors) for a single subject (subject 1). B, Frequency histogram over five subjects in the hippocampus (Hip) and adjacent parahippocampal gyrus (PHG). Note, in the hippocampus, a multimodal distribution in the high-frequency range with three main peaks in the gamma, ripples, and fast ripple range. In contrast, in the parahippocampal gyrus, only one single-frequency band was dominant in the gamma range between 40 and 130 Hz. C, In individual events i and ii, hippocampal ripple/sharp wave complexes and parahippocampal gamma oscillations (gamma 1) were not coincident within a time window of 100 ms. Nevertheless, in event iii, parahippocampal gamma oscillations (gamma 2) immediately followed hippocampal ripple/sharp wave complexes. D, Average time–frequency maps of gamma events not following (n = 115 events, gamma 1) or following (n = 43 events, gamma 2) ripple/sharp waves in three subjects. E, Ripple onset-triggered histograms of gamma oscillations (n = 288 ripples in 5 subjects).