Discovering how seals sleep with half their brain

A study published this month in the Journal of Neuroscience has identified some of the chemicals released in the brain that allow seals to sleep with only one half of their brain at a time.

On land, seals sleep in the same way as humans, with the whole brain.  But when they are in water, seals are able to literally be half-asleep: at any time only one hemisphere of their brain is ‘sleeping’ while the other is still awake.  This allows them to stay relatively aware of the environment while conserving energy.

Researchers at the University of Toronto and UCLA studied the chemicals involved in this amazing biological process by measuring the levels of different substances in the awake and asleep sides of the brain.  They had previously found hemispheric differences in levels of acetylcholine, an important neurotransmitter in the brain. There were low levels of acetylcholine on the sleeping side of the brain and higher levels in the awake side, suggesting that acetylcholine may be behind brain alertness.  In contrast, in the current study, they showed that serotonin (another neurotransmitter) was at similar levels in both sides of the brain, despite being thought to be involved in brain arousal.  It did not seem to impact on whether the side of the brain was waking or sleeping.

As well as being fascinating insights into how seals are able to sleep like this, this research could have implications in treating sleep problems in humans.  By deducing which chemicals are involved in waking and sleeping, treatments could be devised for insomnia and other sleep disorders.  But unfortunately, the only time we humans can be half-asleep is during lectures.