title: Intrusions of a drowsy mind: neural markers of phenomenological unpredictability.
abstract: The transition from a relaxed to a drowsy state of mind is often accompanied by hypnagogic experiences: most commonly, perceptual imagery, but also linguistic intrusions, i.e., the sudden emergence of unpredictable anomalies in the stream of inner speech. This study has sought to describe the contents of such intrusions, to verify their association with the progression of sleep onset, and to investigate the electroencephalographic processes associated with linguistic intrusions as opposed to more common hypnagogic perceptual imagery. A single participant attended 10 experimental sessions in the EEG laboratory, where he was allowed to drift into a drowsy state of mind, while maintaining metacognition of his own experiences. Once a linguistic intrusion or a noticeable perceptual image occurred, the participant pressed a button and reported it verbally. An increase in the EEG-defined depth of drowsiness as assessed by the Hori system of sleep onset was observed in the last 20 s before a button press. Likewise, EEG Dimension of Activation values decreased before the button press, indicating that the occurrence of cognitively incongruous experiences coincides with the rapid change of EEG predictability patterns. EEG hemispheric asymmetry analysis showed that linguistic intrusions had a higher alpha and gamma power in the left hemisphere electrodes, whereas perceptual imagery reports were associated with a higher beta power over the right hemisphere. These findings indicate that the modality as well as the incongruence of drowsiness-related hypnagogic experiences is strongly associated with distinct EEG signatures in this participant. Sleep onset may provide a unique possibility to study the neural mechanisms accompanying the fragmentation of the stream of consciousness in healthy individuals.
authors: Cognition and Brain Sciences Unit, Medical Research Council Cambridge, UK ; Department of Psychology, University of Cambridge Cambridge, UK.
authors: Valdas
authors: V
authors: Noreika
authors: Cognition and Brain Sciences Unit, Medical Research Council Cambridge, UK ; Laboratory of Cognitive and Social Neuroscience, Universidad Diego Portales Santiago, Chile.
authors: Andrés
authors: A
authors: Canales-Johnson
authors: Department of Medicine, University of Cambridge Cambridge, UK.
authors: Justin
authors: J
authors: Koh
authors: Hills Road Sixth Form College Cambridge, UK.
authors: Mae
authors: M
authors: Taylor
authors: Departments of English and Comparative Literature, University at Buffalo Buffalo, NY, USA.
authors: Irving
authors: I
authors: Massey
authors: Cognition and Brain Sciences Unit, Medical Research Council Cambridge, UK ; Department of Psychology, University of Cambridge Cambridge, UK.
authors: Tristan A
authors: TA
authors: Bekinschtein
keywords: EEG Dimension of Activation; EEG spectral power; Hori stages of sleep onset; consciousness; drowsiness; hypnagogic experiences; linguistic intrusions; perceptual imagery