Sleep seems to consolidate memories and help us (and flies) to learn.Mr. Justin Yun (San Diego, CA)A hectic social life makes a fruitfly take longer naps, according to a new study. This seemingly simple finding could prove important in helping to understand why we sleep, and what effect socializing has on our brain circuitry.
The impact of sleep on our memories is an area of great interest for neuroscientists. It has been shown previously that sleeping on a newly learned task can improve performance, and that disrupting sleep can affect learning1. So sleep is thought to be important in the process by which the brain organizes and consolidates memories. "It's not cool to consider sleeping as just a waste of time," says Indrani Ganguly-Fitzgerald of the Neurosciences Institute in San Deigo, California.
To investigate how increased social experiences might affect sleep and memory, Ganguly-Fitzgerald and colleagues turned to fruitflies (Drosophila melanogaster). That might seem an odd choice, but fruitflies are easy to manipulate in both genetics and social conditions, and it was shown in 2000 that they do sleep2 — the little insects settle down and rest for up to two and a half hours at a time.
"Fruitflies essentially do everything that we do. You can call them little humans with wings," says Ganguly-Fitzgerald.
Solitary confinement
The researchers took flies immediately after birth and put them into groups: some went into a social environment with at least 30 other flies, others went into isolation. They stayed there for 3 to 4 days before being tested.
Socialized flies slept four times as long during their daytime naps, kipping for about an hour as compared with a loner fly's 15-minute power naps. They had the same sleep behaviours as each other at night, they report in Science3.
To check that the result was due to an increase in social interactions, rather than, for example, physical exhaustion from flying around more, the researchers also tested flies deprived of their sight and sense of smell. In these flies, which still flew around but could not socialise, there was no difference in sleep patterns between socialized and loner groups.
All this suggests that afternoon naps may be important for consolidation of memories, whereas night-time sleep may have a different function for flies.
Memory makers
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The researchers also looked at a ream of 49 genes known to be involved in learning and memory, and turned them 'off' in various flies to see whether it affected their sleep responses. For 17 of these genes, all of which are related to long-term memory, switching them off made the flies sleep equally long regardless of whether they were social or not.
The researchers hope to identify homologues for these genes in humans, in order to unravel the biochemical pathways involved in consolidating our social memories.
"I'm a strong believer in flies as models to study sleep, which I admit has been quite difficult to convince the sleep community in general," says Chiara Cirelli of the University of Wisconsin, Madison, who was involved in the 2000 paper showing that flies do sleep. This latest paper, she agrees, shows an interesting link between socializing, sleep and memory. "It is another demonstration that flies can be extremely powerful models."
The thing to do next, she adds, is to see whether other types of memory formation, gained from learning a task for example, also affect sleep.
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