Beta EEG reflects sensory processing in active wakefulness and homeostatic sleep drive in quiet wakefulness

摘要

Markers of sleep drive (<10Hz; slow wave activity and theta) have been identified in the course of slow wave sleep (SWS) and wakefulness. So far, higher frequencies in the waking electroencephalogram have not been examined thoroughly as a function of sleep drive. Here, we measured EEG dynamics in epochs of active wake (AW; wake characterized by high muscle tone) or quiet wake (QW; wake characterized by low muscle tone). We hypothesized that the higher beta oscillations (15-35Hz, measured by local field potential and electroencephalography) represent fundamentally different processes in AW and QW.In AW, sensory-stimulation elevated beta activity in parallel with gamma (80-90Hz) activity, indicative of cognitive processing. In QW, beta activity paralleled slow wave activity (1-4Hz) and theta (5-8Hz) in tracking sleep need. Cerebral lactate concentration, a measure of cerebral glucose utilization, increased during AW whereas it declined during QW. Mathematical modeling of state-dependent dynamics of cortical lactate concentration was more precisely predictive when QW and AW were included as two distinct substates rather than a uniform state of wakefulness. The extent to which lactate concentration declined in QW and increased in AW was proportionate to the amount of beta activity.These data distinguish QW from AW. QW, particularly when characterized by beta activity, is permissive to metabolic and electrophysiological changes that occur in SWS. These data urge further studies on state dependent beta oscillations across species.