Figure 2. Coupled theta and gamma oscillations.

(A) Single trial examples (from different subjects) show multiple, brief bursts of high-frequency activity throughout encoding and maintenance, concurrent with theta oscillations. For each trial, we show the raw LFP, high frequency filtered signal, and theta filtered signal (relatively scaled for visualization) centered around one of the bursts. Note the diversity in the center frequencies of bursts, both within and across subjects. Across all subjects, burst duration was 107 ± 18 ms (mean ± s.e.m.) in PCx, and 98 ± 14 ms in AH (see Methods).

(B) PAC during encoding and maintenance was quantified across a wide range of candidate modulating frequencies (top panel) and modulated frequencies (bottom panel). Across evaluated frequencies, we show the percentage of subjects demonstrating significant modulation strength (surrogate test, corrected across modulated sub-bands, p < 0.025), separately for PCx and AH. See also Figure S2.

(C) In both regions of interest, theta power during encoding and maintenance were individually greater vs. baseline (paired-sample t-test, *p < 0.05). Larger solid circles indicate supra-threshold theta power; smaller empty circles indicate sub-threshold power (see Methods). See also Figure S3.

(D) Modulation strengths of theta phase-coupled gamma bursts were increased during encoding and maintenance vs. baseline, which was further stratified for identity-match correct (hit + correct rejection [CR]) vs. incorrect (miss + false alarm [FA]) trials. Larger solid circles indicate significant modulation strength (corrected, p < 0.025). **p < 0.01; ***p < 0.001. See also Figure S3D.

In (C-D), colors indicate individual subjects.