Dopamine (dope-UH-mean)
	Dopamine, a nuerotransmitter, is released in your brain in response to pleasurable stimuli. The less likely or predictable a reward is, the more active your dopamine neurons become and the longer they fire -- flooding your brain with a soft euphoria. Dopamine is also released in response to the mere expection of a reward. But if an expected reward fails to arrive, the dopamine dries up instantly, which can make for a wrenching, and rapid, swing into depression.