An illustration of a sleeping worm (above) where most neurons are quiet (blue dots) and an awake worm (below) in which the nerve cells are active (yellow dots) ANNIKA NICHOLS AND MANUEL ZIMMERAcross the animal kingdom, nearly all creatures sleep or display sleep-like states. The roundworm, Caenorhabditis elegans, does not sleep in a typical day-night cycle like humans and many other animals. Instead, these worms catch most of their z’s while transitioning from one larval stage to another, during a period called lethargus. When these creatures fall asleep, most of their neurons become inactive spontaneously, suggesting that sleep—at least in worms—is a passive state of the brain, according to a study published today (June 22) in Science.
“The condition between sleep to wakefulness is probably one of the most drastic changes that our brains undergo,” says Manuel Zimmer, a neuroscientist at the Research Institute of Molecular Pathology at the Vienna Biocenter in Austria. “How a brain can switch between such drastically different states is not really understood.”
To investigate this process, Zimmer and colleagues examined the brains of C. elegans. These worms do indeed have primitive brains, yet their nervous system comprises only 302 neurons, making it much easier to tackle than, say, the human brain, with billions of neurons, or even the fly brain, which has around 100,000 nerve cells.
Using transgenic worms engineered with a fluorescent indicator that becomes active in response to high calcium levels in neurons (a proxy ...
