…this temporary learning deficit could be traced to a remarkable change that occurs at puberty in the hippocampus, a region of the brain that is involved in remembering places and integrating other kinds of learning. The change affects the GABA neurotransmitter system. GABA, which is present in all mammals, inhibits or down-regulates nerve signals, as opposed to exciting them; this calming, relaxing system is activated by tranquilizers like Valium and the popular sleep drug Ambien, which attach to GABA receptors and act similarly to GABA. But at puberty, female mice experience a 700% increase in an unusual GABA receptor that helps calm the nervous system, except when under stress.
GABA is not the only neurotransmitter system that goes out of whack at puberty, Giedd notes. Recent studies at Harvard suggest that dopamine receptors also temporarily proliferate, a change that might be related to the impulsiveness and risk-taking behaviors seen in teens. These bursts of brain changes seem to be connected to developmentally sensitive periods, says Giedd.