Busy people like to say that the best time to sleep is when you’re dead. But the best time to sleep is actually when you’re young, a study of fruit flies suggests.
Newly hatched fruit flies deprived of sleep end up with brain and behavior problems later in life, scientists report in the April 18 Science. “This study is a really important advance in our understanding of how sleep and brain maturation are related,” says neuroscientist Salome Kurth of the University of Colorado Boulder.
It’s not clear whether sleep trouble early in life has similar effects in people. If so, the implications are provocative, says neuroscientist Megan Hagenauer of the University of Michigan in Ann Arbor. “They suggest that the consequences of chronic sleep deprivation in human children may go beyond temporary impairment and actually produce permanently altered brain development,” she says.
Researchers have previously linked poor sleep in young children to negative outcomes such as anxiety and diminished academic performance, but those results come from observational studies that can’t say whether disrupted sleep actually caused the deficits. The new study in flies, however, makes a causal connection.
Like human infants, rat pups and many other immature animals, young fruit flies sleep more than older ones. Neuroscientist Amita Sehgal of the University of Pennsylvania in Philadelphia and colleagues found that sleep during early life is particularly important.
The team studied the sleep of flies on their first day out of their pupal cases. These young flies slept about four hours longer per day than older flies, fell asleep earlier and were harder to wake up.
Sehgal and her colleagues found the signal in the brain that sends young flies to sleep. A brain structure called the dorsal fan-shaped body produces more sleepiness in young flies than in older flies, the team found. These sleep signals are held in check by a group of neurons that produce the neural chemical dopamine. Young flies have less dopamine in their brains than do older flies. This dearth of dopamine allows the fan-shaped body to send its sleepy message, the team found.
When the researchers disrupted youngsters’ early sleep by genetically altering these dopamine neurons in the brain, male fruit flies’ behavior at the ripe old age of 5 days suffered: Males spent less time courting females and were less likely to mate, compared with males that slept well early in life. The researchers haven’t studied how early sleep deprivation affects female brains and behaviors.
Early sleep deprivation also made its mark in the brain. A brain structure thought to be involved in courtship behavior was about 20 percent smaller in the flies that didn’t get enough sleep early in life than in flies that slept well. This region, called the VA1v glomerulus, does a lot of growing when flies are young, the researchers found. Disrupted sleep seemed to impair its growth.
The results highlight not only the importance of sleep, but also of dopamine, Sehgal says. Because the neurotransmitter also promotes wakefulness in people, drugs that affect dopamine levels, including some stimulants given to children for attention deficit disorders, might damage children’s sleep, she says.