Joyce Chen ’23
Circadian rhythms are notably known as the body’s master clock. They regulate important physical and behavioral effects within the body by reacting to light and darkness. Interestingly, an individual’s preference for being an early bird or a night owl is determined by circadian preference, also known as chronotype. Chronotype impacts the desire for earlier or later sleep by combining circadian rhythms and an individual’s level of sleepiness. Despite the extensive research surrounding circadian rhythms, not much is known about the effects of chronotype on brain function. Dr. Mohammad Ali Salehinejad of the Leibniz Research Centre for Working Environment and Human Factors led a research study to investigate the relationship between circadian preference and neurophysiology.
The research team recruited a total of 32 female participants and divided them into two groups: early chronotypes (ECs), or morning types, and late chronotypes (LCs), or evening types. The circadian rhythms of the two groups were assessed at two specific times in the morning and night in order to analyze the preferred and non-preferred times. During the morning session, both groups were instructed to wake at 8AM, when the chronotypes have the lowest activity, and to sleep at 10-11PM in order to get 8 or more hours of sleep. In contrast, the rules of the evening sessions allowed the participants to sleep at any time before 12AM and to get more than 8 hours of sleep. While the participants completed one reaction time task and three memory tasks, the research team assessed the participants’ motor cortical excitability (the brain’s reaction to its surroundings), neuroplasticity, and cognition. Careful monitoring of the collected data revealed that both groups showed higher motor responses and brain activity at their circadian-preferred times compared to their non-preferred times. Furthermore, it was reported that working memory (short-term memory) and attention had greater performances with the preferred times.
The results of the study can improve the working environment and enhance productivity. Based on circadian preference, certain workspaces can find ways to improve their workers’ health, attention, and motor skills by having them work at their preferred times. Consequently, Dr. Salehinejad and his research team’s study paves the way for future research to better understand the effects of sleep on cognitive performance.
 M.A. Salehinejad, et al., Cognitive functions and underlying parameters of human brain physiology are associated with chronotype. Nat Commun 12, 4672 (2021). doi: 10.1038/s41467-021-24885-0