The phases of the menstrual cycle seem to affect how the brain responds to reward activity, according to a report published online Jan. 31 in the 

Proceedings of the National Academy of Sciences

Karen Faith Berman, MD, and colleagues from the National Institute of Mental Health in Bethesda, Md., studied brain activity in 15 women using functional magnetic resonance imaging to determine how estrogen and progesterone influence the human reward system. While neurons in this system have receptors for both hormones, little is known about how changing hormone levels affect neural activity. 

Using a hypothetical monetary reward game, the investigators found that reward system neurons were more active 4 to 8 days after the onset of menstruation, a time when estrogen is present without progesterone. The activity changes were concentrated in the midbrain, striatum, and left frontopolar cortex. Brain activity in males responded differently highlighting sex-specific differences in the reward system. 

Dreher JC, Schmidt PJ, Kohn P, et al. Menstrual cycle phase modulates reward-related neural function in women. 

The phases of the menstrual cycle seem to affect how the brain responds to reward activity, according to a report published online Jan. 31 in the Proceedings of the National Academy of Sciences Early Edition.