This makes the species ideal for studying the changes in synapses that happen during sleep. elegans has one of the most streamlined nervous systems of any organism, says L’Etoile, and scientists have mapped its entire connectome - the web of all of the neurons and their connecting synapses.
Part of the process of consolidating memories involves reducing the number of synapses during sleep, which is thought to balance connections between neurons in the brain and keep them within an appropriate range. Memories are thought to reside in synapses - the junctions between neurons.
“Their feeding is reduced, but it’s not zero,” she says. Although they tend not to move around, the worms can’t resist sleep eating. While napping, “the little worms become straight with just a little crook where their head is”, says L’Etoile. The researchers used video-based imaging tools to observe hundreds of worms and look for telltale features of sleep such as reduced movement, stereotypical postures and seeming to ‘wake up’ when exposed to a flashing blue light. elegans from one that is awake is a tricky task. With no limbs or clear-cut sleep stages to observe, distinguishing a sleeping C. The research came with an unusual challenge, says L’Etoile: defining when the one-millimetre-long worms are in fact asleep. “We know their individual synapses, and that’s something that we don't have in other animals.” Studying sleep in such a simple organism “might help us to really understand the underlying mechanism”, says Hanna Zwaka, a neuroscientist at Harvard University in Cambridge, Massachusetts. L’Etoile and her colleagues wanted to investigate whether this also applied to C. Research on many species, including fruit flies 2, bees 3, rodents 4 and humans has shown that sleep is essential for long-term memory. “This brings cellular resolution to a question that’s ancient”, namely what is the purpose of sleep and how is it linked to memory, says study co-author Noelle L’Etoile, a cell biologist at the University of California, San Francisco. The findings, published in Cell on 2 June 1, pave the way for scientists to delve more into the processes that occur at the cellular and molecular level during sleep. But disturbing their sleep prevents crucial changes to their nervous system that are involved in forming long-lasting memories. elegans) nematodes can still remember to do so after 16 hours, as long as their post-training nap is uninterrupted. When trained to avoid a sweet scent, Caenorhabditis elegans ( C. Roundworms need a good night’s sleep to maintain the memories associated with particular smells, a study suggests. Credit: Steve Gschmeissner/Science Photo Library
elegans worms have a critical sleep window of 1–2 hours after odour training, during which they solidify their memories.
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