Higher levels of progesterone, a natural steroid hormone, during a menstrual cycle could be linked with brain activity that makes it harder to tell one emotional situation from another, relating also with a lower mood overall, a study has found. The findings, published in the journal Psychological Medicine, show how natural levels of the ovarian hormones 'estradiol' and 'progesterone' can influence brain regions involved in emotion control, and whether this could help explain differences in mood. Emotion control is the ability to regulate behaviour in response to emotional information, particularly when automatic emotional responses need to be overridden.

"In our study we found that higher progesterone levels were linked to brain activity patterns that made it harder to tell different emotion control situations apart, which also corresponded with lower mood in participants," lead author Macia Buades-Rotger, from the University of Barcelona in Spain, said.

An analysis of MRI scan data from 116 naturally cycling women participants revealed that when progesterone levels were higher, there was a less clear distinction between 'easy' and 'difficult' emotional situations in the brain scans.

"This suggests that if the brain can tell different emotional situations apart more clearly, it may be better at regulating emotion in daily life," Buades-Rotger said.

The lead author added that while a one-time measurement cannot establish a cause-and-effect link, the findings are exciting "because we know something about progesterone that we didn't know before." The participants completed questionnaires about their mood and period stage, and gave a saliva sample for measuring hormone levels. They then underwent an MRI scan while conducting a psychological task that stimulated an 'easy' or a 'difficult' emotional response.

For the task, the women were shown a happy face or an angry face and asked to react naturally -- to approach the happy face and avoid the angry face -- or counter intuitively, which was to avoid the happy face and approach the angry face.

All the participants experienced the four different scenarios in the task, the researchers said.

An analysis of brain activity patterns revealed that it was possible to tell whether an 'easy' or a 'difficult' emotional response was elicited from the participant at that moment, they said.

However, when progesterone levels were higher, patterns in one area of the brain called the 'lateral frontal pole' were found to be more similar to one another, suggesting that the brain was less able to differentiate between the 'easy' or 'difficult' task demands.

The authors "observed that lower frontopolar decodability of emotion-action contingencies is a progesterone-sensitive correlate of mood variation."

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