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Neuroimage. 2015 May 15;112:105-113. doi: 10.1016/j.neuroimage.2015.02.056. Epub 2015 Mar 4.

Bistability breaks-off deterministic responses to intracortical stimulation during non-REM sleep.

Author information

1
Department of Biomedical and Clinical Sciences "L. Sacco", Università degli Studi di Milano, Via G.B. Grassi 74, 20157 Milan, Italy.
2
Centre of Epilepsy Surgery "C. Munari", Department of Neuroscience, Niguarda Hospital, Piazza Ospedale Maggiore 3, 20162 Milan, Italy.
3
Max Planck Institute for Human Development, Lentzeallee 94, 14195 Berlin, Germany.
4
Neuroscience Center, University of Helsinki, P.O. Box 56, FIN-00014 Helsinki, Finland.
5
Department of Biomedical and Clinical Sciences "L. Sacco", Università degli Studi di Milano, Via G.B. Grassi 74, 20157 Milan, Italy; Don C Gnocchi Foundation IRCCS, Via Alfonso Capecelatro 66, 20148 Milan, Italy. Electronic address: marcello.massimini@unimi.it.

Abstract

During non-rapid eye movement (NREM) sleep (stage N3), when consciousness fades, cortico-cortical interactions are impaired while neurons are still active and reactive. Why is this? We compared cortico-cortical evoked-potentials recorded during wakefulness and NREM by means of time-frequency analysis and phase-locking measures in 8 epileptic patients undergoing intra-cerebral stimulations/recordings for clinical evaluation. We observed that, while during wakefulness electrical stimulation triggers a chain of deterministic phase-locked activations in its cortical targets, during NREM the same input induces a slow wave associated with an OFF-period (suppression of power>20Hz), possibly reflecting a neuronal down-state. Crucially, after the OFF-period, cortical activity resumes to wakefulness-like levels, but the deterministic effects of the initial input are lost, as indicated by a sharp drop of phase-locked activity. These findings suggest that the intrinsic tendency of cortical neurons to fall into a down-state after a transient activation (i.e. bistability) prevents the emergence of stable patterns of causal interactions among cortical areas during NREM. Besides sleep, the same basic neurophysiological dynamics may play a role in pathological conditions in which thalamo-cortical information integration and consciousness are impaired in spite of preserved neuronal activity.

KEYWORDS:

Causality; Consciousness; Down-state; Intracranial; Phase-locking

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