Swallowing a retort when someone snaps at you is a small daily miracle of self-control. New research suggests that one of the body’s own hormones may make the machinery behind it slightly hazier. A study published in Psychological Medicine scanned the brains of 116 healthy young women and found that those with higher natural levels of progesterone showed weaker, less distinct activity in a region called the lateral frontal pole, which helps suppress automatic emotional reactions. Women with the fuzziest signals there also reported worse moods over the previous week—and the blurred signal statistically accounted for the link between the hormone and low mood. The study is careful, however, to stop well short of claiming causation.
That hormones such as estrogen and progesterone shift mood is old news; how they do it inside the brain is not. The researchers, working with naturally cycling women aged 18 to 35, used a sharper scanning technique than most earlier work. Instead of asking merely whether a brain region switched on or off, they read patterns of activity across many points of tissue and tested whether those patterns could reliably tell one kind of emotional situation from another.
The task was deliberately awkward. Photographs of angry and happy faces flashed up while participants lay in the scanner. Sometimes the rules followed instinct—approach the happy face, avoid the angry one. Sometimes they flipped, demanding that a woman approach an angry face and avoid a happy one, forcing the brain to override its pull towards reward and away from threat. As expected, people were slower and less accurate when the rules clashed with instinct, confirming that the game measured emotional self-control rather than something else. Beforehand each woman gave a saliva sample to measure progesterone and estradiol; afterwards she filled in a questionnaire about her mood over the past week.
A dimmer switch, not a blowout
Several brain regions passed the pattern test, but the frontal pole stood out. Earlier work has tied it to reining in approach-and-avoidance urges, and weak activity there has been found in people with anxiety, trauma symptoms and aggression. As progesterone rose, the region’s signal for “this is an approach situation” versus “this is an avoid situation” grew muddier. The muddier it was, the worse the mood. An alternative explanation—that brain activity was driving mood by altering hormone levels, rather than the reverse—did not hold up statistically. Estradiol, the other ovarian hormone measured, showed no clear link to mood or performance.
Two caveats deserve emphasis. First, progesterone had no bearing on how fast or accurately the women actually played the game: the hormone appeared in the brain’s signal and in reported feelings, not in behaviour. Second, the effect on mood was modest—about 7% of the variation in mood scores—leaving most of the ebb and flow unexplained. The authors note the study had limited power to detect effects smaller than the one observed.
One detail quietly rebukes folk wisdom. Cycle phase itself—whether a woman was early or late in her cycle—did not reliably predict mood or brain activity; the directly measured hormone level was the more precise marker. Broad assumptions about “that time of the month” may simply be missing the actual signal.
The limits are real. Hormones were measured once, not tracked across cycles, so the snapshot cannot separate fleeting hormonal states from stable traits. Saliva-based estradiol readings are imprecise, the chewing gum used to stimulate saliva can skew hormone levels, and cycle phase was estimated from self-reported cycle length. Being cross-sectional, the study can suggest a mechanism but cannot prove progesterone causes anything. It was no treatment trial, though the authors point to brain-stimulation of the frontal pole as a possible future avenue: earlier studies suggest targeting the region can improve such tasks and perhaps ease social anxiety. The paper credits a 2022 Young Investigator Award from the Brain & Behavior Research Foundation, reports no competing interests, and discloses—commendably plainly—that ChatGPT assisted with literature synthesis and data analysis, with the authors reviewing and taking responsibility for the result.
Emotional self-control tends to go unnoticed until it fails. If progesterone does nudge this circuit towards a fuzzier state, it could help explain why some women feel emotionally less sure-footed at certain points in their cycle when nothing else has changed. That is not grounds for alarm. It is grounds for treating hormone-linked mood swings as brain biology rather than as noise.