Scientists Identify Brain Chemicals Behind Seals' Ability to Sleep With Half a Brain

Seals sleep by resting only half of their brain at a time, just like dolphins and whales. Now, a new study has identified some brain chemicals that allow half of the seal's brain to sleep, while the other half remains alert.

"Seals do something biologically amazing - they sleep with half their brain at a time," researcher John Peever, from the University of Toronto, Canada, said in a statement.

"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."

Peever and his colleagues said that their findings might explain these unique biological mechanisms.

For the study, Peever's colleague, doctoral student Jennifer Lapierre, measured how different brain chemicals change in the sleeping and waking sides of the brain in fur seals. She found that the brain chemical acetylcholine was at low levels on the sleeping side of the seals' brain, but it was at high levels on the waking side. This suggests that the chemical could be responsible for brain alertness on the side that is awake.

The research team also found another important brain chemical called serotonin that was present in equal levels on both sides of the brain, irrespective of the seals being either awake or asleep. It was surprising for the scientists, as they have long thought that the chemical causes brain arousal.

Researchers believe the study could have possible human health implications and help scientists understand which brain chemicals function to keep people awake or asleep.

The findings of the study are published in the Journal of Neuroscience.