Alpha oscillations reduce temporal long-range dependence in spontaneous human brain activity.

Ongoing neural dynamics comprise both frequency-specific oscillations and broadband-features such as long-range-dependency (LRD). Despite both being behaviorally relevant, little is known about their potential interactions. In humans, 8-12Hz α-oscillations constitute the strongest deviation from 1/f power-law scaling, the signature of LRD. We postulated that α-oscillations - believed to exert active inhibitory gating - down-modulate the temporal width of LRD in slower ongoing brain activity. In two independent "resting-state" data-sets (electroencephalography surface-recordings and magneto-encephalography source-reconstructions), both across space and dynamically over time, power of α-activity co-varied with the power-slope below 5Hz; i.e., greater α-activity shortened LRD. Causality of α-activity dynamics was implied by its temporal precedence over changes of slope. A model where power-law fluctuations of the α-envelope inhibit baseline-activity closely replicated our results. Thus, α-oscillations may provide an active control mechanism to adaptively regulate LRD of brain activity at slow temporal scales, thereby shaping internal states and cognitive processes.SIGNIFICANCE STATEMENTThe two prominent features of ongoing brain activity are oscillations and temporal long-range dependence. Both shape behavioral performance but little is known about their interaction. Here, we demonstrate such an interaction in EEG and MEG recordings of task-free human brain activity. Specifically, we show that spontaneous dynamics in alpha activity explain ensuing variations of dependence in the low and ultra-low frequency range. In modeling, two features of alpha-oscillations are critical to account for the observed effects on long-range dependence, scale-free properties of alpha oscillations themselves and a modulation of baseline levels, presumably inhibitory. Both these properties have been observed empirically, and our study hence establishes alpha oscillations as a regulatory mechanism governing long-range dependence or "memory" in slow ongoing brain activity.