Diurnal Fluctuations in Testosterone Tied to Variation in Intrinsic Functional Connectivity in a Densely Sampled Male

Sex hormones are powerful neuromodulators of learning and memory, influencing the brain at the level of microscopic intracellular events to macroscopic brain organization. A central feature of the mammalian endocrine system is that hormone secretion varies over time. Human neuroimaging studies that densely sample individuals over timescales of days, weeks, and months provide unique insight into the role our endocrine system plays in regulating the dynamic properties of the human brain. For example, we recently established estrogen’s ability to drive widespread patterns of connectivity and enhance the global efficiency of large-scale brain networks in a densely-sampled female (Pritschet et al., 2020). In men, sex hormone production follows a sinusoidal pattern with a peak in testosterone between 6-7am and nadir between 7-8pm.