Spark

by John J. Ratey

One explanation, certainly, is that physical activity increases levels of tryptophan in the bloodstream and thus concentrations of serotonin in the brain. It also balances dopamine, norepinephrine, and synaptic mediators such as BDNF. By stabilizing such a broad number of variables, exercise helps to tone down the ripple effects of shifting hormones. Exercise also ties into a more nuanced theory of PMS that is just developing. Estrogen and progesterone both get transformed into dozens of hormonal derivatives, some of which are of great interest to neuroscientists because they regulate the brain’s major excitatory and inhibitory neurotransmitters—glutamate and gamma-aminobutyric acid (GABA). During the hormonal fluctuations of the premenstrual phase, the levels of these derivatives relative to one another can get out of whack, which can lead to too much excitement of the nerve cells in the brain’s emotional circuitry. This could happen because too much glutamate is being produced or not enough GABA, but either way, the runaway activity can lead to mood changes, anxiety attacks, aggression, and even seizures. One recent study found that while hormone levels were the same in women with and without PMS symptoms, their GABA levels were different. Exercise has widespread effects on the GABA system, which puts the brakes on excessive cellular activity as Xanax does. Studies in rats have shown that just one bout of exercise turns on the genes that produce GABA, for instance. Exerc...