Comparative Electrocorticographic Signatures of S‑Ketamine and Racemic Ketamine in the Rat Visual Cortex Across Temporal Phases.

Ketamine enantiomers differ neurophysiologically, yet their specific influence on sensory cortical oscillations remains unclear. Characterizing the electrophysiological signatures of S-ketamine (KS) versus racemic ketamine (KSR) in the visual cortexa region highly sensitive to NMDA blockadecan improve understanding of enantiomer-specific neural modulation and anesthetic depth. This study compared the temporal dynamics of cortical oscillations induced by KS and KSR in rat visual cortices during dissociative anesthesia. Adult Wistar rats received KS (50 mg/kg), KSR (50 mg/kg), or saline. Visual cortex electrocorticographic (ECoG) recordings were obtained for 15 min, segmented into three phases. Power spectral density was calculated across delta to gamma bands (1-40 Hz), and linear power means were compared. KSR produced a deep, stable suppression of oscillatory activity across all frequency bands throughout the recording. Conversely, KS exhibited time-dependent modulation, with a pronounced late-phase increase in delta and theta power, indicating anesthetic superficialization. Furthermore, KS preserved relatively higher overall beta and gamma power, whereas KSR displayed a persistent high-beta elevation (24-28 Hz) typical of NMDA blockade. Ultimately, KSR maintains a stable suppressive pattern, while KS produces late-phase enhancement of slow rhythms. These distinct electrophysiological profiles highlight enantiomer-specific neural dynamics relevant for anesthetic choice and mechanistic modeling.