A collaboration between scientists at the University of Toronto and University of California, Los Angeles, has discovered a biological phenomenon in seal brains that may help refine research into sleep factors among other mammals. The findings were published this month in the Journal of Neuroscience.
Study co-author John Peever, associate professor of biology at U of T, said researchers discovered that seals have the ability to be both asleep and awake simultaneously.
While at rest in water, Peever said one half of a seal's brain will subside into a state of slumber while the other will remain active and alert. The entire brain would shut down when the seal went to sleep on land, he added.
The phenomenon, Peever said, is likely an adaptive behaviour designed to help the animals ward off prey that attacks from underwater.
"If they were to sleep with both halves of their brain, they would effectively be vulnerable to being eaten," he said in a telephone interview.
"The side of their brain that's looking down into the water is ... the side that's watching, and the eye that's looking up into the sky where there's no harm coming from typically is the side that is sleeping."
While such behaviour is not unique to seals — certain species of whales have acquired the same skill — Peever said the smaller mammals may serve as a guide to solving some of the mysteries underlying human sleep patterns.
Both seals and humans are large-brained mammals that can be safely compared, he said, adding the chemicals that regulate sleep patterns in one may prove equally powerful in the other species.
Preliminary findings, he said, have already challenged some of the common wisdom surrounding sleep drivers.
When comparing both sides of the seal brain, researchers found serotonin levels were nearly equal in the sleeping and wakeful halves.
Peever said this finding casts doubt on the broadly held theory that serotonin is the chemical primarily responsible for keeping the brain aroused and in a wakeful state. The data suggests a chemical known as acetylcholine may play a more active role. Peever said acetylcholine levels were more elevated in the active half of the brain and much lower on the sleeping side.
Such analysis has been difficult to conduct on humans, whose entire brains go off-line when they settle down for some shut-eye.
By studying a comparable species who can maintain both states at the same time, Peever said researchers may be able to make some useful discoveries that ultimately pave the way for human sleep treatments.
"It's a guide to tell us what are the transmitters that are involved in keeping the brain awake and those that are keeping it asleep, and it's a first line of understanding the basic chemistry of the brain that drives that process," he said.
The research team is currently analyzing histamine levels in seal brains to determine what role, if any, it plays in sleep patterns.
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