INTRODUCTION: The injection of ketamine is an animal model of schizophrenia. It leads to behavioral changes such as hyperlocomotion and accelerated breath and electrophysiological changes such as the appearance of high‑frequency oscillations (HFO). Previous studies reported that the amplitude of HFO in the striatum is coupled with a phase of respiratory rhythm. However, recent studies suggest that the olfactory bulb is an important generator of HFO which can impose this activity in ventral striatal areas. AIM(S): The purpose of this study was to examine the LFP recording from olfactory bulb after injection of ketamine with a novel method of phase-amplitude coupling detection. METHOD(S): The proposed novel method of PAC detection is based on analysis of time‑frequency representation of signals aligned to a given phase in the low‑frequency band. Low‑frequency wave is obtained with the Matching Pursuit algorithm by selecting waveforms of interest. The time‑frequency representation of the signal’s energy density is derived from continuous wavelet transform and normalized at each frequency relative to its average value in the baseline period. Next, the representation is thresholded at values obtained from surrogate data. The resulting maps are used to compute comodulograms. The effects presented in the comodulograms are validated with extreme values statistics. RESULTS: We found statistically significant coupling between the amplitude of high‑frequency oscillation (around 150 Hz) and phase of low‑frequency oscillation (around 7 Hz) in most of the examined rats. The temporal pattern of PAC shows dependence on injection of ketamine. CONCLUSIONS: The HFO in olfactory bulb display the property of phase-amplitude coupling with low-frequency oscillation. The additional conclusion is that the proposed novel method is adequate to detect coupling in real LFP data.
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