A recently published study has found that females show greater brain activation to uncertain rewards during the most fertile stage of the menstrual cycle, perhaps explaining why women dress more attractively and have altered sexual preferences during this time.
The dopamine system is known to be involved in reward processing, and one of the current theories is that it is particularly involved in reward prediction – that is, it signals when we might expect to find something gratifying.
The key female sex hormone estrogen is known to alter dopamine function, so it was thought that females might show changes in how they experience rewards when estrogen levels fluctuate during the menstrual cycle.
The most direct dopamine-related rewards are drugs like cocaine and amphetamine, and studies have found that the same dose feels stronger during the fertile follicular phase of the cycle.
Research, largely conducted with straight women, has found that females dress more attractively during this phase and have altered sexual preferences so that they experience more masculine looking, assertive males as more attractive.
This new study by Dr Jean-Claude Dreher and colleagues fMRI brain-scanned men and women during a gambling task, and looked at between-sex differences and within-cycle differences in brain activity.
They found that women have a greater response to rewards than men in the amygdala and hippocampus, both key emotion areas.
They also found that during the most fertile follicular phase of the menstrual cycle, women show more activity when predicting rewards, particularly in the amygdala and another key emotion and reward area, the orbitofrontal cortex.
When the reward was delivered (a win in the gambling task), women showed stronger response in a number of reward-related areas during the fertile phase, including the striatum, a dopamine-rich deep brain area.
It seems that the hormone cycle makes brain areas related to the prediction and experience of rewards become more active when women are more fertile. This might explain why the menstrual cycle can alter women’s sexual preferences and behaviour.
If you want more details of the study, the full paper is available at the link below.
Link to PubMed entry for the scientific paper.
pdf of full-text scientific paper.