Circadian rhythms govern diverse aspects of physiology, including sleep/wake cycles, cognition, gene expression, temperature regulation, and endocrine signaling. Similarly, studies of brain function in both humans and animals have documented time of day–dependent variation at multiple scales of brain organization.
Despite the clear influence of circadian rhythms on physiology, most studies of brain function do not report or consider the impact of time of day on their findings.
A new study suggests that the strength of the brain’s global signal fluctuation shows an unexpected decrease as the day progresses.
Scientists analyzed functional magnetic resonance imaging (fMRI) data of approximately 900 subjects who were scanned between 8 am and 10 pm on two different days as part of the Human Connectome Project.