Suzana Herculano-Houzel

PMS explains, but doesn’t justify

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Premenstrual tension may be a woman’s thing, but it’s a problem that ends up affecting everyone – because it always affects those around us, man or woman, boy or girl. Not all women get irritable during the premenstrual period – thank goodness! – to the point where it’s a disorder that requires medical help. In principle, however, all women are subject to these mood swings, even to a small degree, for a simple reason: they result from the effects on the brain of the change in the hormone progesterone that leads to menstruation.

Progesterone accumulates in the blood each menstrual cycle after ovulation, produced by the corpus luteum that accompanies the egg. In the days leading up to menstruation, it is this hormone that causes the inner lining of the uterus to thicken in preparation for the implantation of an embryo.

Its functions don’t end there, however. When it reaches the brain, progesterone acts as a powerful natural anxiolytic for women: it increases the brain’s ability to regulate anxiety and the stress response in general. In the premenstrual period, when the corpus luteum degenerates and the level of progesterone in the blood drops dramatically, this natural anxiolytic effect is lost, and the brain becomes more susceptible to stress, anxiety and depression.

Not all women are affected in the same way. The monthly absence of the natural anxiolytic hormone from the body is more drastic in some women who, probably for genetic reasons, have a smaller number of receptors in the brain that respond to progesterone. For them, any drop in the hormone leads to a significant loss of the natural anxiolytic effect and, as a result, these women become especially irritable in the premenstrual period, capable of reacting to the slightest threat with an intense stress response, responding aggressively even to innocuous gestures and comments.

Hormonal irritation, however, is not a “license to kill”. Even if the temporary loss of anxiolytic progesterone explains aggression, it doesn’t justify any kind of rude behavior. The reason is simple: we are all able to use the services of the prefrontal cortex to control our impulses. The first step to mastering them is to become aware of them. Hormones have a voice, yes – but the brain speaks louder.

Originally published in Folha de São Paulo on August, 2006

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