Decoding Ketamine’s Neurophysiology Under General Anesthesia: Insights for Targeted Therapeutics

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This study demonstrates that coadministration of ketamine with general anesthesia (GA) differentially modulates neurophysiologic EEG signatures, selectively preserving beta-gamma oscillations while suppressing theta augmentation. This dissociation suggests distinct neural pathways for ketamine’s diverse effects, opening new avenues for more targeted treatments for depression and pain without loss of consciousness.

Study Background

Ketamine has emerged as a unique pharmacological agent with dissociative, analgesic, and rapid antidepressant properties. Clinically, it is used both in subanesthetic doses for treatment-resistant depression and in anesthetic settings for procedural sedation or surgery. Despite its efficacy, the intricate neurophysiologic mechanisms by which ketamine produces its diverse effects, particularly its psychedelic and antidepressant outcomes, remain incompletely understood.

Importantly, specific cortical oscillatory patterns recorded via electroencephalography (EEG)—notably theta (θ) and beta-gamma (βγ) frequency bands—have been linked to discrete effects of ketamine such as altered perception, analgesia, and mood modulation. Understanding whether these neurophysiologic signatures can be modulated independently is critical for refining therapeutic strategies and minimizing side effects.

Study Design

This cohort study was a secondary analysis of participant-level data derived from three prospective studies conducted between 2017 and 2023 at the University of Michigan, Stanford University, and the University of Auckland. The combined cohorts included healthy volunteers, elective surgery patients, and individuals diagnosed with depression, all aged 18 years or older.

Participants received either a subanesthetic infusion of ketamine at 0.5 mg/kg over 40 minutes or placebo, administered either during wakefulness or under general anesthesia. The primary outcome measured changes in EEG power spectra across multiple frequency bands, focusing on theta and beta-gamma oscillations, using paired nonparametric statistical analysis (Wilcoxon signed-rank test).

Key Findings

The analysis included 52 participants in the primary cohort (mean age 43.4 years; 65.4% female) and 27 participants in a supplementary cohort (mean age 30.2 years; 55.6% female). Ketamine-induced EEG changes were consistently modulated by GA across all primary cohort participants.

Specifically, ketamine administered during wakefulness significantly increased theta power (mean increase from 17.3 to 22.9 dB) and beta-gamma power (mean increase from 6.3 to 11.6 dB). Under general anesthesia, however, the theta augmentation observed during awake ketamine infusion was not evident; theta power nonsignificantly decreased during ketamine administration (from 29.0 to 27.8 dB). Conversely, beta-gamma oscillation modulation by ketamine was preserved during anesthesia, with an increase from 8.5 to 11.2 dB comparable to the awake condition.

This dissociation suggests that ketamine’s neurophysiologic effects tied to beta-gamma oscillations are independent of conscious awareness, whereas theta augmentation appears related to cortical activity disrupted by anesthesia-induced unconsciousness.

Expert Commentary

These findings provide valuable mechanistic insight into how ketamine’s distinct oscillatory signatures relate to its multifaceted behavioral effects. The preservation of beta-gamma modulation under anesthesia may underpin ketamine’s analgesic and possibly antidepressant actions that do not require conscious perception, whereas theta oscillations may be more connected with dissociative and perceptual experiences requiring intact consciousness.

Expert opinion underscores the translational potential of this work: selectively modulating specific neurophysiologic pathways could inform development of novel treatments that maximize ketamine’s therapeutic benefits while mitigating adverse psychoactive effects. The study, however, is limited by sample size, heterogeneity of participant groups, and indirect neurophysiologic inference from surface EEG. Further research employing advanced neuroimaging and larger, more homogenous cohorts is warranted.

Conclusion

This investigation distinguishes discrete neurophysiologic components of ketamine’s action by showing that general anesthesia dissociates the theta and beta-gamma EEG signatures associated with ketamine’s effects. This delineation advances understanding of ketamine’s mechanism of action and supports potential targeted interventions to enhance clinical outcomes in anesthesia, pain management, and psychiatry.

By parsing the neural substrates underpinning ketamine’s diverse actions, clinicians and researchers may better tailor dosing, coadministration strategies, and drug development efforts toward more efficacious and tolerable therapies in neuropsychiatric and perioperative care.

Funding and ClinicalTrials.gov

The original studies were conducted with institutional support from the University of Michigan, Stanford University, and the University of Auckland. Specific funding details were not provided. There is no direct reference to ClinicalTrials.gov registration numbers in the analyzed publication.

References

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