Intrusions of a drowsy mind: neural markers of phenomenological unpredictability.
Frontiers in psychology January 1, 2015 Valdas Noreika, Andrés Canales-Johnson, Justin Koh et al.
During the transition from relaxation to drowsiness, people often experience hypnagogic phenomena such as perceptual imagery or linguistic intrusions—sudden, unpredictable anomalies in inner speech. In a single participant across 10 EEG sessions, drowsiness depth (measured by Hori stages) increased in the 20 seconds before reporting such an experience, and EEG Dimension of Activation values decreased, indicating rapid changes in brain predictability. Linguistic intrusions were associated with higher alpha and gamma power over the left hemisphere, while perceptual imagery corresponded to higher beta power over the right hemisphere. These results suggest that the modality and incongruence of hypnagogic experiences have distinct EEG signatures, and sleep onset offers a way to study the neural basis of consciousness fragmentation in healthy individuals.