Figure 3: Amygdala-hippocampus directional PAC and phase lag analysis.

(a) PAC comodulogram for differences between the aversive and the neutral conditions is shown, with warmer colours denoting higher z-scores. The high gamma amplitude in the hippocampus was phase-locked to the phase of amygdala low-frequency (theta and alpha) rhythms (all P<0.01, permutation test). In contrast, the reciprocal directional PAC modulation (for example, high gamma amplitude in the amygdala phase-locked to phase of hippocampal low-frequency activity) was nearly absent. (b) Phase lag analysis. The PAC modulation index between low-frequency phase and high gamma amplitude was estimated across time lags for the aversive condition. The red line represents the z-PAC between subject-specific amygdala low-frequency phase and hippocampal high gamma amplitude (70–180 Hz). The blue line denotes the z-PAC between hippocampus low-frequency phase and amygdala high gamma amplitude. Cross (+) denotes subjects who showed the amygdala low-frequency activity leading hippocampal gamma.