Sleep Switch: Induce Sleep By Remote Control And Consolidate Memory

in medicine, biology

When did you sleep last night? How long did you sleep? Is it hard to wake up on Monday mornings? Instead of turning on an alarm clock, you may be able to turn on some cells, a sleep switch, in the brain to wake you up from that deep early morning sleep!

Scientists at the Washington Universtiy School of Medicine in St. Louis report that they discovered a switch in the brain to control sleep.  However, not in man, but in fruit flies! According to these Scientists, there is a group of approximately 20 cells in the brains of fruit flies that controls when and how long the flies sleep.

If you can switch the sleep switch off, your insomnia may be gone too.

The significance of the finding does not remain in sleep control alone, they say that slumber induced through this sleep switch was essential to the creation of long-term memory, directly proving a connection between memory and sleep that scientists have long suspected.

sleep switch and long term memory The paper is published in the June 24 issue of the scholarly journal Science.

"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 neurobiology. "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.

In scientific terms, they induced sleep on demand by expressing the temperature-gated nonspecific cation channel Transient receptor potential cation channel (UAS-TrpA1) in neurons, including those with projections to the dorsal fan-shaped body. When the temperature was raised to 31°C, flies entered a quiescent state that meets the criteria for identifying sleep. When sleep was induced for 4 hours after a massed-training protocol for courtship conditioning that is not capable of inducing long-term memory by itself, flies develop  long-term memory . Activating the dorsal fan-shaped body in the absence of sleep did not result in the formation of LTM after massed training.

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 the process called courtship 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.

According the National Institute of Neurological Disorders and Stroke, at least 40 million Americans each year suffer from chronic, long-term sleep disorders each year, and an additional 20 million experience occasional sleeping problems. These disorders and the resulting sleep deprivation interfere with work, driving, and social activities. They also account for an estimated $16 billion in medical costs each year, while the indirect costs due to lost productivity and other factors are probably much greater.

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 cells they singled out can be matched to other brain cell types based on the chemical messengers they produce.

Source article:  Inducing sleep by remote control facilitates memory consolidation in Drosophila. Donlea JM, Thimgan MS, Suzuki Y, Gottschalk L, Shaw PJ.Science, June 24, 2011. DOI: 10.1126/science.1202249.
 

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