The young shouldn’t be scolded for sleeping a lot, a new study says. This research in flies shows that long snoozes are critical to proper brain development, including the ability to mate. Young flies sleep more than their older counterparts and are especially resistant to arousal. The role heavy sleep plays in their development has been elusive, as have the mechanisms in place to maintain it. Matthew S. Kayser and colleagues, studying the increased sleep behavior of young flies, performed a series of experiments that led them to theorize that dopamine signaling is less active in young organisms, which in turn allows a sleep-promoting region of their brain, the dorsal fan shaped body (dFSB), to be hyperactive. To test their theory, they activated the dFSB in young and mature flies during the first 12 hours of the day -- the period when the two age groups exhibit the most differences in sleep patterns. In young flies, the boost in dFSB activation didn’t have much effect, but in mature flies, it caused a big increase in nap time. This is consistent with the theory that the dFSB is very active in young flies, such that boosting its activity wouldn’t make much difference. The researchers looked to see if sleep resulted in changes in function on a larger scale, focusing on courtship, an activity thought to be hardwired. Exciting the dopamine neurons during day one of a fly’s life -- when its dopamine neurons should have been quiet -- caused courtship troubles for young flies later in life; these flies mated much less frequently, for example. The work of Kayser et al. defines a specific function for heavy slumber in young flies. Dopamine may influence developmental changes in sleep in other species, too, the researchers say. 

"A Critical Period of Sleep for Development of Courtship Circuitry and Behavior in Drosophila," by M.S. Kayser; Z. Yue; A. Sehgal at Perelman School of Medicine at the University of Pennsylvania in Philadelphia, PA; Z. Yue; A. Sehgal at Howard Hughes Medical Institute in Philadelphia, PA.