Bistability Breaks-Off Deterministic Responses to Intracortical Stimulation During non-REM Sleep

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

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cerebral Cortex / physiopathology*
  • Consciousness / physiology
  • Drug Resistant Epilepsy / physiopathology
  • Electric Stimulation
  • Electrodes, Implanted
  • Electroencephalography
  • Evoked Potentials
  • Humans
  • Neural Pathways / physiology
  • Neurons
  • Sleep*
  • Thalamus / physiology
  • Unconsciousness / physiopathology