Gamma, beta, alpha rhythms — cross-frequency coupling and neural synchrony
Cortical oscillations reflect synchronized activity of large neural populations, visible in the local field potential (LFP) and EEG. Alpha (~8–13 Hz) dominates during relaxed states and suppresses task-irrelevant areas; beta (~13–30 Hz) is prominent during motor planning and top-down control; gamma (~30–100 Hz) accompanies active sensory processing and is generated by E-I network interactions (PING mechanism: pyramidal-interneuron gamma). A key phenomenon is phase-amplitude coupling (PAC): the amplitude of fast gamma oscillations is modulated by the phase of slower theta or alpha waves — a mechanism for multiplexing information across temporal scales. The modulation index (MI) quantifies the degree of this cross-frequency coupling.