Figure 1. Theta-nested gamma rhythms enhance hippocampal SWRs in vivo.
(A) Representative LFP recording in an awake mouse illustrates the occurrence of different network states in a behavioral-dependent manner. The initial spontaneous SWRs during a quiet state (left, SWR) are replaced by a running-associated theta-nested gamma rhythm (middle), followed by another rapid reversal to SWRs (right, p-SWR). Note the higher amplitude of the p-SWRs. Prolonged running period is marked by the black bar above. (B) (i, ii, iii) Left, three example excerpts from the trace in (A) at higher temporal resolution. (i) Left, the initial quiet state example band-pass filtered at 2–300 Hz and 100–300 Hz to illustrate the SWRs and the corresponding ripple component, respectively. Two SWRs are accentuated in red. Right, a single SWR together with its wavelet transform (color-coded power spectral density with superimposed corresponding ripple trace in white). (ii) Left, the theta-nested gamma example with a small excerpt shown above. Right, the corresponding spectral analysis demonstrates the predominant theta (7.3 Hz) and gamma (46.3 Hz) peak. (iii), the p-SWR with the same type of illustration as for the SWR shown in (i). (C) Left, a direct comparison of the mean values of SWR areas before and after the intervening gamma episode (n = 11, 4 mice) highlight a significant increase in SWR areas (p=0.0006, Wilcoxon signed rank test). The respective grand means are indicated by the horizontal bold bars. Right, the corresponding percentage increase of mean SWR areas.