Abstract
BACKGROUND: Chronotype is the circadian time preference for sleep-wake timings. However, its impact on cognitive performance is least explored. OBJECTIVE: The present study investigated the effect of chronotype (morning "M" vs. evening "E") on cognitive measures as a function of time of the day. In addition, the correlation between electroencephalogram (EEG) waves and subjective/objective cognitive measures were investigated. METHOD: Cognitive status of 28 adult male subjects (15 "M" and 13 "E") was assessed objectively through event-related potential (ERP) by administering visual odd ball paradigm test and subjectively through Montreal Cognitive Assessment questionnaire. In addition, 20 to 30 min of resting EEG was recorded. Recordings were done from 8 to 10 am and from 4 to 6 pm on a single day. Power spectral analysis of EEG for alpha and beta waves at PZ and FZ cortical sites was done after subjecting selected epochs to fast Fourier transformation. Also, latency and amplitude of P300 potential from event-related potential record were measured. Appropriate statistical tests were applied for analysis. RESULTS: Higher alpha and beta power was observed in "E" at PZ in the evening. "M" showed increased P300 latency and amplitude during evening session for frequent and rare stimuli and vice versa in "E."' Significant negative correlation was seen between latency of rare stimuli and alpha and beta power at FZ site during evening in "E" chronotype only. CONCLUSION: Result indicates better attention and alertness during evening hours in evening chronotypes and vice versa in morning chronotypes. The findings could be implemented to schedule the mental performance/cognitive load according to individual chronotype.