When scientists genetically tweaked a part of the brain involved in learning and memory in fruit flies, the flies were unimpaired even after being deprived of sleep.
The study appears in Current Biology on Aug. 5.
The study was the first to show that fruit flies enter a state of inactivity comparable to sleep. The research team demonstrated that the flies have periods of inactivity where greater stimulation is required to rouse them.
These periods begin at night; like human sleep they are cyclic over the course of the night, with sleep cycles lasting 20-25 minutes.
lso like humans, flies deprived of sleep one day will try to make up for the lost time by sleeping more the next day, a phenomenon referred to as increased sleep drive or sleep debt.
For the study, first author Laurent Seugnet, Ph.D., a postdoctoral fellow, revealed that sleep deprivation impairs learning in flies. Seugnet put them through multiple runs of a maze with two options: one lighted vial with the bitter-tasting quinine in it and one darkened but quinine-free vial. Flies are instinctively drawn to light, but they want to avoid the unpleasant taste of quinine.
"This tests the flies' mental capacity in two ways: First, they've got to remember that the lighted vial is the one that has quinine in it, and then they've got to suppress their natural instinct to fly toward the light," says Seugnet.
Flies allowed normal sleep learned to avoid the lighted vial, but sleep-deprived flies did not.
A brain messenger known as dopamine is linked to some of the mental capabilities harmed by sleep loss. Researchers decided to test if this messenger could be used to block learning impairment in sleep-deprived flies.
Seugnet genetically altered a line of flies so they made more copies of a dopamine receptor in brain regions known as the mushroom bodies. These areas are roughly equivalent to the human hippocampus, which is involved in learning and memory.
Sleep-deprived flies with extra dopamine receptors could still learn as if they had a full night's sleep, Seugnet found.