Abstracts

Rationale: Interaction between different frequency bands ("Cross Frequency Coupling (CFC)") is thought to be important for information processing and integration in human brain. During slow wave sleep (SWS), CFC would be more apparent. However, detailed spatio-temporal dynamics of CFC in sleep has yet to be elucidated by human electrocorticogram (ECoG). Methods: Nine medically intractable epilepsy patients with ECoG recording for epilepsy surgery participated (IRB R0603). ECoG was recorded during a whole night with scalp EEG, electrooculogram and electromyogram of the chin. Thirty-second segments were classified into different sleep stages by means of R&K criteria. Slow frequency band (0.02-2 Hz) was divided into 15 bins, while fast frequency band (40-200 Hz) was divided into 4 bins using band pass filter. Instantaneous amplitude (IA: real number) of each fast frequency bin and instantaneous phase (IP: complex number) of each slow frequency bin were calculated using Hilbert transformation. Absolute values of correlation coefficients between IA and IP were calculated for all combinations of the bins in each electrode. For statistical analysis, 10,000 surrogate random time-shifted signals were generated to determine the threshold (p < 0.05). Electrodes with supra-threshold CFC were defined as E+CFC. Seizure onset zone or area with interictal spikes was defined as epileptic area. Results: Among the whole electrodes investigated (612) across the patients, the number of E+CFC increased as sleep stage became deep SWS (341), REM sleep (177), light sleep (LS) (169), and waking (78). Within non-epileptic areas, E+CFC were less in the temporal lobe (TL) than in the frontal (FL) and the parieto-occipital lobes (POL) during LS and REM (p < 0.05). In contrast, there was no significant interlobar difference during SWS. In epileptic areas, CFCs were less observed compared with non-epileptic areas during SWS and LS (p < 0.05). Conclusions: CFCs widely appeared in SWS whereas they were found in the smaller areas in TL than in FL and POL during both LS and REM. E+CFC tended to be less in epileptic area compared with non-epileptic area during SWS and LS, thus epileptiform discharges might interrupt physiological CFCs. Funding: KAKENHI JP 15H05874 15H05875