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Diurnal variation in alpha oscillations and aperiodic components of patient ECoG

Poster Session D - Monday, March 9, 2026, 8:00 – 10:00 am PDT, Fairview/Kitsilano Ballroom

Kemmei hoshi¹ (), Ayumu Yamashita¹, Ryohei Nakayama¹, Masataka Sawayama², Takumitsu Iwata³, Satoru Oshino³, Naoki Tani³, Hui Ming Khoo³, Ryohei Fukuma^3,4, Haruhiko Kishima^3,5, Takufumi Yanagisawa^3,4,5, Kaoru Amano¹; ¹Graduate School of Information Science and Technology, The University of Tokyo, ²Graduate School of Information Science and Technology, ³Graduate School of Medicine, Osaka University, ⁴Institute for Advanced Co-Creation Studies, Osaka University, ⁵Osaka University Hospital Epilepsy Center

Neural activity in the cerebral cortex shows both rhythmic oscillations and 1/f aperiodic components. Alpha-band (8–13 Hz) activity is dominantly observed over the occipital cortex, and numerous studies have reported its association with cognitive functions such as vision and attention. The slope of the EEG aperiodic component has been suggested to reflect the excitation/inhibition (E/I) balance. Some cognitive performances are known to fluctuate across the day, with peaks around 10:00–11:00 or 17:00–20:00. Time-varying dynamics of alpha oscillations and aperiodic components may involve such diurnal fluctuation in cognitive functions. In this study, we analyzed long-term, multichannel electrocorticogram (ECoG) recordings from ten epilepsy patients with chronically implanted intracranial electrodes. We quantitatively investigated the diurnal variations in the alpha oscillation frequency and the slope of the 1/f component. The alpha peak frequency over occipital regions, defined as the frequency yielding maximal occipital alpha power, exhibited a clear diurnal rhythm: it gradually increased during the day and peaked around 19:00–21:00, while some patients showed an additional peak around 9:00–15:00. In contrast, the slope of the 1/f components showed multiphasic fluctuation patterns, with peaks around 9:00, 20:00, and possibly 13:00 across many electrodes and patients. These results demonstrate that both periodic and aperiodic components of human intracranial neural activity exhibit diurnal fluctuations. They also suggest that considering such daily rhythms will be important for future cognitive experiments, neural state estimation, and clinical applications. Furthermore, the observed neural fluctuations may be associated with diurnal variations in cognitive performance, warranting further investigation of this relationship.

Topic Area: PERCEPTION & ACTION: Vision