Scientists have found that the natural level of the hormone progesterone in young women is linked to how clearly the brain distinguishes the signals needed to control emotional reactions. The work was published in the journal Psychological Medicine.
In everyday life people often act automatically: they are drawn to what is pleasant and avoid what is unpleasant. Psychologists call this approach-avoidance behavior. But sometimes one must do the opposite - for example, approach an angry colleague even though one wants to move away. Such overcoming of automaticity requires active emotional control.
This function is largely handled by the lateral frontal pole - a region of the cortex at the front of the brain, directly behind the forehead. Previous work showed that this area helps suppress automatic impulses during emotional choice.
The new study involved 116 healthy women aged 18 to 35 who were not using hormonal contraceptives and had no neurological or mental disorders. Their saliva was taken to measure estradiol and progesterone levels, and they also underwent functional magnetic resonance imaging (fMRI) - a method that tracks brain activity via changes in blood flow. Participants performed a task in which they had to pull closer or push away faces with a joyful or angry expression. In half the cases the instruction matched natural impulses, and in half it contradicted them.
When the instruction contradicted the impulse, the women reacted more slowly and made more errors. The scientists then analyzed brain scans from 106 participants using multivoxel pattern analysis. A voxel is a tiny three-dimensional unit of brain tissue, the equivalent of a pixel. A machine learning algorithm tried to predict, from the activity pattern of thousands of voxels, which task the woman was performing at a given moment.
Activity in several areas, including the lateral frontal pole and the striatum (a cluster of neurons deep in the brain involved in controlling movement and reward), allowed the algorithm to determine more accurately than chance guessing whether a participant was suppressing an automatic impulse. At the same time, in women with higher progesterone levels this accuracy was lower: the correlation coefficient was -0.25 for the frontal area and -0.26 for the striatum. A correlation is a statistical relationship that by itself does not prove causation.
Clearer activity patterns in the lateral frontal pole were associated with better mood over the past week (r = 0.26). No direct correlation was found between progesterone and mood, but a mediation analysis revealed an indirect link: high progesterone was associated with less distinct frontal patterns, and those in turn with worse mood. The model explained 7.1% of the variation in mood.
Contrary to expectations, estradiol levels were not linked to either the accuracy of decoding brain activity or mood. The hormones also did not correlate with the speed or correctness of task performance.
The authors emphasize: the study does not prove that progesterone directly causes changes in the brain or mood. The data were collected once, and there were 101 participants with complete data instead of the planned 120, which reduced statistical power to 71%. In addition, chewing gum was used to stimulate salivation, which may affect hormone measurement.
Elevated progesterone does not mean that a woman becomes more emotional or controls her behavior worse, stressed the head of the work, Macia Buades-Rotger. According to him, only statistical associations were observed, and hormonal effects vary greatly between individuals. The scientists plan to follow the same women across different phases of the cycle in order to separate temporary hormonal states from stable traits.