Sociable fruit flies apparently need more sleep than their isolated siblings. The find, reported tomorrow in Science, provides clues about why flies and other animals sleep and what our brains do while we are in dreamland.
Although animals of all sorts need sleep to survive, it is still a mystery why we require regular shut-eye. Studies in humans, rats, and other animals have suggested that sleep plays a role in learning and memory--students who have a full night's sleep between training sessions for a new skill learn faster than those who don't, for example (ScienceNOW 14 April, 1998).
To see if they could find a link between sleep and nervous-system stimulation, neuroscientist Indrani Ganguly-Fitzgerald of the Neurosciences Institute in San Diego, California, and her colleagues compared the sleep habits of flies housed in groups of 30 or more to those of flies kept in isolation. Despite their simple appearance, flies have rich social lives, she says: "They mate, they fight. They form memories about the interactions they've had, and they make decisions." And, the researchers found, the socialized flies slept significantly more during the day than their isolated counterparts. In fact, the bigger the group, the more sleep the flies needed.
Ganguly-Fitzgerald argues that the difference is due to the flies' social life. All that extra stimulation requires extra down-time to process, she says. When the scientists tested flies that couldn't see or smell--and therefore received less sensory input in the socialized conditions--there was no difference between socialized and isolated insects.
Further experiments demonstrated that molecules and genes involved in learning and memory also impact the social flies' extra need for naps. One of those molecules is a neurotransmitter called dopamine. When flies were altered to have more or less dopamine than normal, the difference between social and isolated flies disappeared. The same was true when flies lacked genes involved in memory formation.
The results "support the idea that sleep is involved in synaptic plasticity," the process in which brain cells make new connections, says neurobiologist Amita Sehgal of the University of Pennsylvania Medical School in Philadelphia. New experiences trigger changes in brain-cell connections, and that apparently increases the need for sleep, she says. The role of dopamine and memory-forming genes is intriguing, she says, and further experiments should help nail down exactly which genes are involved in the link between sleep and information-processing.
Related sites
)
)
)
)
)
)
)
)
