EEG Functional Connectivity Detects Seasonal Changes

Seasonal alterations in human health, mood, and basal cortisol level have been reported in several studies. Despite the interest in these factors, seasonal changes in brain functional connectivity as a possible base of these phenomena have not been studied before. The aim of the current study is to analyse seasonal effects using two resting electroencephalogram (EEG) functional connectivity measures: magnitude-squared coherence (MSC) and imaginary coherence (iCOH). Recordings from 80 healthy Estonians were used: 25 recordings from spring, 8 from summer, 10 from autumn and 37 from winter months. Eyes-closed resting EEG was recorded from 30 channels using Neuroscan Synamps2 acquisition system and five frequency bands were analysed: delta, theta, alpha, beta and gamma. Multivariate permutation test revealed significant influence of seasons on beta MSC. Furthermore, statistical analysis between different seasons showed increased beta MSC in spring and winter months compared to summer and autumn months, increased beta iCOH in spring, autumn and winter months compared to summer months and increased gamma MSC in spring and summer months compared to autumn months. The increase in beta MSC and iCOH in spring and winter months compared to summer months may be the result of increased stress or deficiency in Vitamin D. Current study is the first to bring out seasonal changes in brain functional connectivity, but the shortcoming of the study is the limited number of recordings in summer and autumn months. Therefore, further studies are required for more reliable results.