The sex hormone levels heavily influence the brain's reward circuit in a woman during the menstrual cycle, according to a new study by the National Institute of Mental Health (NIMH), a component of the National Institutes of Health (NIH).
The reward circuitry is one of the most complex areas of the brain. It has receptors for both progesterone and estrogen. The circuit is made up of the prefrontal cortex, which is the seat of thinking and planning; the amygdala, which regulates fear; the hippocampus, which is the memory hub and the striatum, which relays signals from these areas to the brain's cortex.
While the receptors for the female sex hormones predominate the circuit, researchers have been unable to determine what role they play in the reward circuit.
The current study says that a woman's brain reward circuit was more active and receptive if they were in a menstrual phase dominated by estrogen, which is just before ovulation takes place. However when both estrogen and progesterone dominated, they appeared to be mood swings and the women was not receptive even when she was rewarded.
The study conducted at the NIMH Intramural Research Program, is reported online in the Proceedings of the National Academy of Sciences.
The research team led by Karen Berman, MD, chief of the NIMH Section on Integrative Neuroimaging, mainly used functional magnetic resonance imaging (fMRI) in order to get images of the brain activity during menstrual phase.
In order to determine the activity of the brain during the menstrual cycle in a woman, the researchers scanned the brain activity of 13 women and 13 men when they were playing the slot machines. The women were scanned twice; before and after ovulation.
It was found that when women were anticipating a reward the amygdala was activated meaning that emotion and reward-related behavior was more pronounced during the pre-ovulation phase. Additionally the more pleasurable areas were activated during this phase rather than the post-ovulatory phase.
On the other hand, men showed a different response to the anticipation of the rewards. They had more activity in the signal relay area than the women.
"These first pictures of sex hormones influencing reward-evoked brain activity in humans may provide insights into menstrual-related mood disorders, women's higher rates of mood and anxiety disorders, and their later onset and less severe course in schizophrenia," said Berman. "The study may also shed light on why women are more vulnerable to addictive drugs during the pre-ovulation phase of the cycle."