Changes in resting activity in the sensory cortices of the brain at dawn and dusk are associated with an improvement in visual perception, shows a study published this week in Nature Communications.
Although the influence of circadian cycles on physiological processes have been documented before, the neural basis of time-of-day dependent changes in human perception are unclear. In this study, Christian Kell and colleagues scanned the brains of 14 male participants at 6 different times (spanning 8am to 11pm) on two subsequent days. In addition to collecting so-called resting state data (which refers to data collected when a participant is not doing a task) the authors also collected functional magnetic resonance imaging data while participants performed a visual detection task. The results showed that the participants were best at the visual task in the morning (at 8am) and in the evening (at 8pm), because at these times, the resting activity in the areas of their brain that process visual information was lower.
The authors suggest that the human brain changes its natural activity in order to compensate for the deterioration in visual-signal quality at dawn and dusk. This anticipatory mechanism may explain why we can still see well at these times.