INTRODUCTION: Fast oscillations recorded in local field potentials (LFP), such as gamma oscillations (30–100 Hz) and high-frequency oscillations (HFOs, 130-180 Hz), are thought to temporally coordinate spiking activity. Ketamine is a psychoactive compound currently under extensive investigation for its antidepressant potential. In rodents, the olfactory bulb (OB) exhibits large-amplitude HFOs following ketamine administration.

AIM(S): How ketamine-induced changes in gamma and HFOs relate to neuronal spike activity.

METHOD(S): LFP data from freely moving rats (N=7) from the OB were acquired using a SmartBox (NeuroNexus, A8 × 8-10 mm-200–200–177). Spike activity were detected with Kilosort4 package. Rats were recorded 20-minute baseline period and 30 minutes of post-injection recording (ketamine, 0.1 mg/kg).

RESULTS: After ketamine administration, a decrease in both gamma bands power and a noticeable increase in HFOs power were observed. Modulation analysis indicated that high-gamma activity was largely replaced by HFOs, implying a reorganization of oscillatory dynamics. CSD analysis, overlaid on the OB histology reveals a distinct spatial patterns for high gamma after ketamine. The peri-stimulus time histogram analysis identified two spike clusters: one showing synchronized activity with gamma oscillations during the baseline and another lacking of such synchronization. Interestingly, spike activity in both clusters coordinated with HFOs after ketamine treatment. Spike-field coherence analysis verified increased spike-phase locking within the post-ketamine administration, indicating improved synchronization between spiking activity and HFOs.

CONCLUSIONS: Ketamine-induced brain oscillations may alter cognitive function by balancing gamma and HFOs activity. The change from gamma synchronization to extensive HFOs may lead to less specificity in brain communication, resulting in altered information processing.

FINANCIAL SUPPORT: The study was funded by NCN (grant 2021/41/B/NZ4/03882).