Diurnal fluctuations in steroid hormones tied to variation in intrinsic functional connectivity in a densely sampled male.

Diurnal variation is an essential biorhythm, yet the relationship between diurnal fluctuations in steroid hormones and the functional architecture of the human brain is virtually unknown. This precision neuroimaging study suggests that endogenous fluctuations in testosterone, estradiol, and cortisol concentrations are tied to rhythmic changes in coherence across the brain. Precision imaging studies that track individuals across major endocrine transitions (e.g. the diurnal cycle and menstrual cycle) demonstrate steroid hormones' ability to modulate the functional architecture of the brain in both sexes, and provide a starting point for future studies to probe the functional significance of these rhythms for behavior.