The Effects of Anesthetics on the Cortex—Lessons From Event-Related Potentials

Abstract

Consciousness while under general anesthesia is a dreadful condition. Various electroencephalogram (EEG)-based technologies have been developed, on the basis of empirical evidence, in order to identify this condition. However, certain electrophysiological phenomena, which seem strongly related with depth of anesthesia in some drugs, appear less consistent with those of other anesthetic drugs. There is a gap between the complexity of the phenomenon of consciousness and its behavioral manifestations, on the one hand, and the empirical nature of the reported electrophysiological markers, which are associated with it, on the other hand. In fact, such a gap might prevent us from progressing toward unified electrophysiological markers of consciousness while under anesthesia, which are applicable to all anesthetic drugs. We believe that there is a need to bridge this conceptual gap. Therefore, in this work, we will try to present a theoretical framework for such bridging. First, we suggest focusing on neuropsychological processes, which seem to have a clear role in the behavioral manifestations of consciousness while under anesthesia but seem, nevertheless, better defined than consciousness itself-such as perception and attention. Then, we suggest analyzing the effects of anesthesia upon these neuropsychological processes, as they are manifested in the EEG signal. Specifically, we will focus on the effects of anesthesia on event-related potentials (ERPs), which seem more easily associable with neuropsychological modeling.

Identifying Recall Under Sedation by a Novel EEG Based Index of Attention—A Pilot Study

“…The underlying hypothesis, which was confirmed in a preliminary manner in this pilot study, was that awareness and recall under anesthetics would involve increased activation of attentional processes. We presented this hypothesis and reviewed its support in the literature, in much detail, in a previous theoretical publication ( 32 ). Electrophysiological markers for attention are well-established in the literature ( 37 ), and we established the ability to extract them in real-time from easy-to-use headsets ( 38 – 45 ).…”

“…If these findings would be replicated, in more elaborative studies, they may offer a refreshing alternative to the currently prevailing markers of AUA and RUS, which are empirical in nature, and are considered imprecise ( 8 ). Specifically, the currently leading markers seem less appropriate for certain anesthetic drugs ( 52 , 53 ), while attention, and attention related markers, seem to be reduced with all anesthetic drugs ( 32 ) and thus may overcome the limitations with the current markers.…”

“…Thus, they can signal when becoming aware and/or uncomfortable ( 5 , 6 , 24 ). Nevertheless, there are certainly procedures and conditions in which it is of clinical importance to monitor the patient's level of awareness under sedation ( 25 – 29 ) and multiple studies aimed at this goal, with limited success ( 30 – 32 ).…”

“…It is reasonable to expect that awareness under anesthesia or sedation, especially of stressing events, might evoke greater activation of attentional processes ( 32 ). It was shown, e.g., by using an auditory oddball protocol, that even though attention related electrophysiological activity reduces with increased dose of multiple anesthetics, it nevertheless remains evident.…”

Vascular and neuronal effects of general anesthesia on the brain: An fMRI study

“…They found that anesthetics cause reduction of N1 and other perception‐related waves that is accompanied by further reduction in P3 and other attention‐related waves. This anesthetic‐induced reduction of attention leads to reduction of top‐down activation of prefrontal to perceptual brain regions and causes loss of consciousness 65 …”