How Seals Sleep with Half their Brains: Chemicals Discovered

Did you know that a seal can sleep with only half of its brain? The other side stays awake, giving it a better chance at survival in the wild. Now, biologists have identified the brain chemicals that allow seals to stay half awake while they snooze.

"Seals do something biologically amazing-they sleep with half their brain at a time. The left side of their brain can sleep while the right side stays awake. Seals sleep this way while they're in water, but they sleep like humans while on land. Our research may explain how this unique biological phenomenon happens," said John Peever, one of the researchers from the University of Toronto, in a press release.

The study, published in the Journal of Neuroscience, was headed by scientists at UCLA and the University of Toronto. In order to conduct their study, the researchers measured how different chemicals change in the sleeping and waking sides of the brain. In particular, they found that acetylcholine, an important chemical, was at low levels on the sleeping side of the brain but at high levels on the waking side. Usually, the chemical is associated with skeletal muscle movement in humans, as well as in the regulation of smooth muscle and cardiac muscle. In the central nervous system, it's thought to be involved with memory, learning and mood.

It wasn't only acetylcholine that they found, though. The researchers also found that another brain chemical, serotonin, was present at equal levels on both sides; it didn't matter if the seals were awake or a sleep. This, in particular, baffled researchers. The chemical is usually associated with brain arousal, so it would have made sense if it were in greater concentrations on the side of the brain that was awake.

These findings don't just have implications for seals, though. About 40 percent of North Americans suffer from sleep problems. Understanding exactly what chemicals help a brain stay awake or keep asleep is crucial for future research concerning the science of sleep.