Individual differences in dominant theta-band frequency during associative memory encoding

Abstract

Individual differences in brain electrophysiologic activity have been recognized a long time ago. Electroencephalographic (EEG) indices such as individual alpha (IAF) and gamma (IGF) frequency have been extensively investigated as biomarkers of individual differences in baseline neurophysiological activity and in response to different stimuli. In contrast, individual differences in dominant theta frequency have received considerably less attention. Given that theta-band EEG activity underlies memory processes, better knowledge of its individual difference, besides improving understanding of the physiology of memory processes, is of foremost importance for personalization of future non-invasive neuromodulation treatment attempts for memory impairments (such as in dementia and other neurodegenerative disorders). The aim of this study was to explore individual differences in individual theta-band frequency (ITF) from a scalp EEG recorded during associative memory (AM) encoding. In a sample of 42 healthy young adults (age 20 – 35; 50% female) we extracted the frequencies (2-10 Hz, in 0.5 Hz steps) with the highest event-related spectral perturbation from 19 overlapping time windows and six centroparietal electrodes from the EEG recorded during successful encoding in the AM task. The ITF was defined as modal frequency (in the 4-8Hz range) in the given time x electrode matrix. The method showed 93% success rate and the range of variability of the extracted ITFs. We present and discuss individual differences in theta-band activity during AM encoding, together with ITF-extraction challenges.