title: Consciousness and cortical responsiveness: a within-state study during non-rapid eye movement sleep.
abstract: When subjects become unconscious, there is a characteristic change in the way the cerebral cortex responds to perturbations, as can be assessed using transcranial magnetic stimulation and electroencephalography (TMS-EEG). For instance, compared to wakefulness, during non-rapid eye movement (NREM) sleep TMS elicits a larger positive-negative wave, fewer phase-locked oscillations, and an overall simpler response. However, many physiological variables also change when subjects go from wake to sleep, anesthesia, or coma. To avoid these confounding factors, we focused on NREM sleep only and measured TMS-evoked EEG responses before awakening the subjects and asking them if they had been conscious (dreaming) or not. As shown here, when subjects reported no conscious experience upon awakening, TMS evoked a larger negative deflection and a shorter phase-locked response compared to when they reported a dream. Moreover, the amplitude of the negative deflection-a hallmark of neuronal bistability according to intracranial studies-was inversely correlated with the length of the dream report (i.e., total word count). These findings suggest that variations in the level of consciousness within the same physiological state are associated with changes in the underlying bistability in cortical circuits.
authors: Department of Psychiatry, University of Wisconsin, Madison, WI, USA.|Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland.
authors: Jaakko O
authors: JO
authors: Nieminen
authors: Department of Psychiatry, University of Wisconsin, Madison, WI, USA.|Department of Psychology, University of Wisconsin, Madison, WI, USA.|Coma Science Group, GIGA-Research &Neurology Department, University and University Hospital of Liege, Liege, Belgium.
authors: Olivia
authors: O
authors: Gosseries
authors: Department of Clinical Sciences "Luigi Sacco", Università degli Studi di Milano, Milan, Italy.|Don C. Gnocchi Foundation IRCCS, Milan, Italy.
authors: Marcello
authors: M
authors: Massimini
authors: Department of Psychiatry, University of Wisconsin, Madison, WI, USA.|Department of Psychology, University of Wisconsin, Madison, WI, USA.
authors: Elyana
authors: E
authors: Saad
authors: Department of Psychiatry, University of Wisconsin, Madison, WI, USA.|Department of Psychology, University of Wisconsin, Madison, WI, USA.
authors: Andrew D
authors: AD
authors: Sheldon
authors: Department of Psychiatry, University of Wisconsin, Madison, WI, USA.|Department of Neurology, University of Wisconsin, Madison, WI, USA.
authors: Melanie
authors: M
authors: Boly
authors: Department of Psychiatry, University of Wisconsin, Madison, WI, USA.|Centre for Investigation and Research on Sleep, Centre Hospitalier Universitaire Vaudois and University of Lausanne, Lausanne, Switzerland.
authors: Francesca
authors: F
authors: Siclari
authors: Department of Psychiatry, University of Wisconsin, Madison, WI, USA.|Department of Psychology, University of Wisconsin, Madison, WI, USA.
authors: Bradley R
authors: BR
authors: Postle
authors: Department of Psychiatry, University of Wisconsin, Madison, WI, USA.
authors: Giulio
authors: G
authors: Tononi
mesh_terms: D002540:Cerebral Cortex / Q000502:physiology; D003243:Consciousness; D004325:Dreams / Q000502:physiology*; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008297:Male; D009473:Neuronal Plasticity; D012890:Sleep / Q000502:physiology; D012895:Sleep, REM / Q000502:physiology*; D009435:Synaptic Transmission; D050781:Transcranial Magnetic Stimulation; D014851:Wakefulness / Q000502:physiology