Time- and frequency-resolved decomposition of beta brain activity reveals two functionally distinct beta bands

Oscillatory brain activity in the beta (13-30 Hz) range plays a central role in sensorimotor and other healthy brain processes and is a potential disease biomarker . However, even in the well-studied sensorimotor system, inconsistencies remain concerning beta’s differential role in maintaining and terminating movement. Emerging evidence suggests that beta comprises two frequency ranges, a lower (<20 Hz) and a higher (>20 Hz) subrange. Moreover, beta occurs in transient ‘events’ which correlate with perception and action. We here use human whole-brain magnetoencephalography (MEG) recordings and a Hidden Markov Model based analysis approach to discover whole-brain beta-band activity during rest and a naturalistic motor task in a data-driven manner. We successfully delineate two anatomically and functionally distinct beta band components which coexist throughout the neocortex. Low-beta (<20 Hz) events are very rare, high amplitude events, whereas high-beta (>20 Hz) is common but lower in amplitude. Both bands show state-specific anatomical distribution and modulation during a motor task: Low-beta is entirely absent during movement, whereas high-beta is only partially suppressed and reoccurs during postural maintenance. During post-movement beta rebound, low-beta event probability increases threefold, accompanied by strong low-beta event synchronization. A third state, probably corresponding to gamma activity, is active during task execution. Beta rebound occurs via a directed, sequential shift from gamma/active state via high-beta state to low-beta state. Our results provide strong experimental evidence for the coexistence of two functionally and anatomically distinct beta bands, and provide insights into their role in movement initiation, maintenance, and termination.