Sex hormones are powerful neuromodulators of learning and memory. In rodents and nonhuman primates estrogen and progesterone influence the central nervous system across a range of spatiotemporal scales. Yet, their influence on the structural and functional architecture of the human brain is largely unknown. Here, I highlight findings from a series of dense-sampling neuroimaging studies from my laboratory designed to probe the dynamic interplay between the nervous and endocrine systems. Individuals underwent brain imaging and venipuncture every 12-24 hours for 30 consecutive days. These procedures were carried out under freely cycling conditions and again under a pharmacological regimen that chronically suppresses sex hormone production. First, resting state fMRI evidence suggests that transient increases in estrogen drive robust increases in functional connectivity across the brain. Time-lagged methods from dynamical systems analysis further reveals that these transient changes in estrogen enhance within-network integration (i.e. global efficiency) in several large-scale brain networks, particularly Default Mode and Dorsal Attention Networks. Next, using high-resolution hippocampal subfield imaging, we found that intrinsic hormone fluctuations and exogenous hormone manipulations can rapidly and dynamically shape medial temporal lobe morphology. Together, these findings suggest that neuroendocrine factors influence the brain over short and protracted timescales.

Menstruation is a normal physiological process in women occurring as a result of changes in two ovarian produced hormones – estrogen and progesterone. As a result of these fluctuations, women experience different symptoms in their bodies – their immune system changes (Sekigawa et al, 2004), there are changes in their cardiovascular and digestive system (Millikan, 2006), as well as skin (Hall and Phillips, 2005). But these hormone fluctuations produce major changes in their behavioral pattern as well causing: anxiety, sadness, heightened irritability and anger (Severino and Moline, 1995) which is usually classified as premenstrual syndrome (PMS). In some cases these symptoms severely impair women’s lives and professional help is required. The official diagnosis according to DSM-5 (2013) is premenstrual dysphoric disorder (PMDD). Despite its ubiquitous presence the origins of PMS and PMDD are poorly understood. Some efforts to understand the underlying brain state during the menstruation cycle were performed by using TMS (Smith et al, 1999; 2002; 2003; Inghilleri et al, 2004; Hausmann et al, 2006). But all of these experiments suffer from major shortcomings - no control groups and small number of subjects. Our plan is to address all of these shortcomings and make this the biggest (to our knowledge) experiment of its kind which will, hopefully, provide us with some much needed answers.