Right-frontal slow negative potentials evoked by occipital TMS are reduced in NREM sleep

Occipital transcranial magnetic stimulation applied in a task-free experimental setup leads to enhanced relative negativity of frontally recorded evoked slow potentials under the influence of caffeine (Murd et al., 2010 [26]). We tested whether this increased negativity could be reversed when a similar magnetic stimulation is applied during quiet sleep where consciousness is absent. Consistently with the hypothesis, non-REM sleep led to relative more positive slow brain potentials, compared to wakefulness. This effect was lateralized to the right hemisphere. We conclude that TMS indeed elicits slow negative potentials in higher arousal states, but the effect has hemispheric specificity depending on how arousal is manipulated.

Research highlights
► Occipital TMS combined with EEG was used to evoke slow cortical potentials (SCPs).
► Conscious state produced negativization of the SCP compared to NREM sleep state.
► The effect spread from occipital to parietal, central and frontal areas.
► The effect was lateralized: SCP negativity was recorded from the right hemisphere.
► SCP appears as a neural correlate of consciousness in the TMS/EEG domain.