Sleep switch found in fruit flies

Rather than count sheep, drink warm milk or listen to soothing music, many insomniacs probably wish for a switch they could flick to put themselves to sleep.

Scientists at Washington University School of Medicine in St. Louis have discovered such a switch in the brains of . In a study appearing June 24 in Science, the researchers show that a group of approximately 20 cells in the brains of fruit flies controls when and how long the flies . Slumber induced through this sleep switch was essential to the creation of , directly proving a connection between memory and sleep that scientists have long suspected.

"This is exciting because this induced sleep state so far appears to be very similar to spontaneous sleep," says Paul Shaw, PhD, associate professor of . "That means we can manipulate these cells to explore a whole new realm of questions about the purposes of sleep. Such studies might one day lead us to more natural ways of inducing sleep in humans."

The key cells are found in an area of the fly brain known as the dorsal fan-shaped body. Scientists in Shaw's lab genetically modified the cells to increase their activity. One effect of making these cells more active was that adult flies slept for an additional seven hours a day.

When scientists added a gene that increases the cells' activity only at warmer temperatures, they could determine when and how long flies would sleep by simply adjusting the temperature in the flies' habitats.

To analyze the similarity of induced sleep to spontaneous sleep, scientists tested whether induced slumber was essential to the formation of long-term memories. In a process called conditioning, male flies were exposed to other males genetically modified to make female sex pheromones.

"The subject fly will initiate courtship because of the female pheromones, but the modified male making those pheromones inevitably rejects him," says first author Jeff Donlea, PhD, now a postdoctoral research assistant at Oxford University. "This is an ecologically relevant way to test memory because a male fly in the wild needs to quickly assess whether a particular female is interested in mating so that he doesn't waste time making unproductive advances."

The researchers used a training protocol that normally only creates a memory that lasts a few hours in fruit flies. After being "rejected" multiple times over three hours, the fly learns not to make advances when he encounters the altered male again at a later time. But when scientists used the cells in the dorsal fan-shaped body to put the fly to sleep immediately after training, the fly formed a long-term memory of his experience that lasted for at least several days.

To rule out the possibility that the increased excitability of the cells could be directly responsible for the long-term memory, scientists activated the sleep-regulating cells following training but prevented the flies from sleeping. The flies did not remember the training, indicating that sleep itself was important for the consolidation of memory.

Scientists have yet to determine whether a counterpart for the dorsal fan-shaped body exists in human brains. Shaw's lab is currently working to see if the they singled out can be matched to other brain cell types based on the chemical messengers they produce.

Related Stories

Searching for shut eye: Study identifies possible sleep gene

Jul 29, 2008

While scientists and physicians know what happens if you don't get six to eight hours of shut-eye a night, investigators have long been puzzled about what controls the actual need for sleep. Researchers at the University ...

Brain tweak lets sleep-deprived flies stay sharp

Jul 31, 2008

Staying awake slows down our brains, scientists have long recognized. Mental performance is at its peak after sleep but inevitably trends downward throughout the day, and sleep deprivation only worsens these effects.

New research sheds light on fly sleep circuit

Nov 26, 2008

In a novel study appearing this week in Neuron, Brandeis researchers identify for the first time a specific set of wake-promoting neurons in fruit flies that are analogous to cells in the much more complex sleep circuit in hum ...

Sleepy Fruit Flies Provide Clues to Learning and Memory

Jun 15, 2006

Researchers at the University of Pennsylvania School of Medicine have discovered that a brain region previously known for its role in learning and memory also serves as the location of sleep regulation in fruit flies. Through ...

Recommended for you

Emotional adjustment following traumatic brain injury

7 hours ago

Life after a traumatic brain injury resulting from a car accident, a bad fall or a neurodegenerative disease changes a person forever. But the injury doesn't solely affect the survivor – the lives of their spouse or partner ...

New ALS associated gene identified using innovative strategy

Oct 22, 2014

Using an innovative exome sequencing strategy, a team of international scientists led by John Landers, PhD, at the University of Massachusetts Medical School has shown that TUBA4A, the gene encoding the Tubulin Alpha 4A protein, ...

User comments