Cortical excitability transiently increases during attentional lapses

It is well established that conscious state modulates cortical excitability, such that wakefulness has lower excitability compared to sleep. However, the impact of conscious content on cortical excitability has mostly been neglected in previous research: one can indeed be conscious without being truly aware of an external stimulus, for instance, during vigilance lapses. Here, we hypothesized that, during a vigilance lapse, the brain reacts to stimuli in a similar way to when it is unconscious. To test this hypothesis, cortical excitability was investigated while performing a continuous vigilance task (Compensatory Tracking Task, CTT) after prolonged wakefulness beyond habitual sleep time. Cortical excitability changes between periods with and without vigilance lapses were inferred from amplitude, slope and peak latencies of the first component of the TMS-evoked EEG potential (TEP; 0–30 ms post-TMS). During lapses vs. no-lapses, we found a significant amplitude increases of TEP and a concomitant significant increase in the latency of TEP positive peak. These results suggest that there is a transient change of cortical excitability during vigilance lapses, pointing to an alteration of the brain similar to the one observed during unconscious states, such as during sleep. Future research should investigate how these changes interfere with sensory processing and cognition and their molecular mechanisms. These findings provide new insight into the brain mechanisms underlying changes in consciousness content and in transient alteration of attention.