In addition to smoothing out wrinkles, researchers have found that the drug Botox can reveal the inner workings of the brain. A new study used it to show that feedback from individual nerve cells controls the release of dopamine, a chemical messenger involved in motivation, memory, and movement.

Such “self-regulation,” the researchers say, stands in contrast to the widely held view that the release of dopamine — known as the “feel good” hormone — by any cell relied on messages from nearby cells to recognize that it is releasing too much of the hormone.

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