Linking neuronal connectivity with brain cross-rhythmic interactions

In the brain, synchronous activity is detected as oscillations at different frequencies. Experimental data from the hippocampus and neocortex link Phase-Amplitude Cross-Frequency Coupling (PAC), where the amplitude of fast gamma oscillations aligns with the phase of slower theta/alpha waves, to cognitive functions like attention, learning and navigation. Traditionally, this mechanism was thought to be generated through the slow oscillation modulating the excitability and thus driving the fast gamma wave amplitude. However, recent findings using the Cross-Frequency Directionality (CFD) metric show that in the hippocampus, gamma amplitude reliably precedes in time the locally measured theta phase (CFD<0). In this talk, we explore how neural connectivity influences these interactions. Specifically, we show that feedforward inhibition modeled by a theta-modulated ING (Interneuron Network Gamma) model results in fast-to-slow interactions. In contrast, feedback inhibition in a theta-modulated PING (Pyramidal Interneuron Network Gamma) model leads to slow-to-fast interactions.