'Seals require only half of their brain to fall asleep'


Scientists from Universities of California, Los Angeles and Toronto (Canada), led a team that identified the chemical cues allowing the seal brain halves to remain awake and asleep.

The findings may explain the biological mechanisms that enable the brain to remain alert during waking hours and go off-line during sleep, the Journal of Neuroscience reports.

"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," says John Peever, professor at Toronto.

"Our research may explain how this unique biological phenomenon happens" adds Peever, according to a Toronto statement.

Jennifer Lapierre, doctoral student at Toronto and study co-author, made this discovery by measuring how different chemicals change in the sleeping and waking sides of the brain.

She found that acetylcholine - an important brain chemical - was at low levels on the sleeping side of the brain but at high levels on the waking side. This finding suggests that acetylcholine may drive brain alertness on the side that is awake.

But, the study also showed that another important brain chemical - serotonin - was present at the equal levels on both sides of the brain whether the seals were awake or asleep. This was a surprising finding because scientist long thought that serotonin was a chemical that causes brain arousal.

"It could help solve the mystery of how and why we sleep," says study's senior author Jerome Siegel from California's Brain Research Institute.