Distinct origins of human low and high alpha rhythms revealed by simultaneous EEG-SEEG

Alpha-band activity is the most prominent neurobiological feature of scalp electroencephalography (EEG) signals, recent findings showed that there is more than one alpha rhythm coexisted in this 8-13 Hz band, but the generation mechanism of them was not fully understood. To address this question, we collected local field potential (LFP) in 32 brain regions of human brain with stereo-EEG (SEEG), with simultaneously recording with EEG during the process from awaked state (eyes-closed) to loss of consciousness (LOC) state with anesthesia. Our study revealed a prominent low-alpha (LA) rhythm (8-10 Hz) localized in the occipital region during the awake, eyes-closed state. As anesthetic depth increased leading to the LOC, this low-alpha rhythm gradually diminished and was replaced by a globally distributed high-alpha (HA) rhythm (10-13 Hz). This phenomenon was consistently observed at both LFP and EEG levels. Furthermore, we demonstrated that state-dependent changes of oscillatory property in alpha band were primarily driven by periodic rather than aperiodic activities, which could be also effectively explained by a simple dynamical model. This work provides the first evidence of anesthetic-induced modulation mechanisms underlying the generation and regulation of distinct alpha oscillations, offering valuable insights for future research in anesthesia, consciousness studies, and potential clinical applications.