Moderate sedation induced by general anaesthetics disrupts audio-spatial feature binding with sustained P3 components in healthy humans

Feature binding is considered to be the basis for conscious stimulus perception, while anaesthetics exert a gradient effect on the loss of consciousness (LOC). By integrating these two streams of research, the present study assessed the effect of two anaesthetic agents (i.e. propofol and midazolam) on audio-spatial feature binding. We also recorded the electrophysiological activity of the frontal channels. Using pharmacokinetic simulation, we determined the effect-site concentration (Ce) of the anaesthetics at loss of response to verbal command and eyelash reflex. We subsequently adjusted Ce to 75%, 50% and 25% of Ce-LOC to achieve deep, moderate and light sedation, respectively. Behavioural results showed that moderate sedation selectively disrupted feature binding. The frontal channels showed a P3 component (350–600 ms peristimulus period) following the presentation of audio-spatial stimuli at baseline and under moderate and light sedations. Critically, the late event-related potential component (600–1000 ms) returned to the pre-activated level (0–350 ms) at baseline and under light sedation but was sustained under moderate sedation. We propose that audio-spatial feature binding may require the presence of a P3 component and its subsequent and sufficient decline, as under anaesthetic-induced moderate sedation the P3 component was sustained and featured binding was impaired.