From Sleep Study, Clues to Happiness - NYTimes.com
A little over a decade ago, scientists discovered that narcolepsy, the neurological disorder that leads to episodes of irresistible sleepiness, is caused by the loss of brain cells that produce hypocretin, a neurotransmitter that promotes wakefulness.
But the discovery did not shed light on two other mysterious problems associated with the disorder. Narcoleptics have profoundly high rates of depression — up to six times the rate in the general population — and they have a tendency to collapse when swept by some emotions, a phenomenon known as cataplexy.
Now research shows that in addition to regulating sleep, hypocretin also appears to govern emotion, particularly experiences of joy and happiness.
The study has implications that extend beyond narcolepsy. It suggests that the brain has several different arousal systems, and that one of them, driven by hypocretin, has the specific function of keeping people awake for pleasure.