Media Releases

New study shows how seals sleep with only half their brain at a time

February 19, 2013

TORONTO, ON – A new study led by an inter­na­tion­al team of biol­o­gists has iden­ti­fied some of the brain chem­i­cals that allow seals to sleep with half of their brain at a time.

The study was pub­lished this month in the Jour­nal of Neu­ro­science and was head­ed by sci­en­tists at UCLA and the Uni­ver­si­ty of Toron­to. It iden­ti­fied the chem­i­cal cues that allow the seal brain to remain half awake and asleep. Find­ings from this study may explain the bio­log­i­cal mech­a­nisms that enable the brain to remain alert dur­ing wak­ing hours and go off-line dur­ing sleep.

“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 Pro­fes­sor John Peev­er of the Uni­ver­si­ty of Toron­to.

The study’s first author, Uni­ver­si­ty of Toron­to PhD stu­dent Jen­nifer Lapierre, 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.

These find­ings have pos­si­ble human health impli­ca­tions because “about 40% of North Amer­i­cans suf­fer from sleep prob­lems and under­stand­ing which brain chem­i­cals func­tion to keep us awake or asleep is a major sci­en­tif­ic advance. It could help solve the mys­tery of how and why we sleep” says the study’s senior author Jerome Siegel of UCLA’s Brain Research Insti­tute.

An abstract of the study can be found online:‑n


For more infor­ma­tion, please con­tact:

Jerome Siegel, PhD
Chief, Neu­ro­bi­ol­o­gy Research
Pro­fes­sor, Psy­chi­a­try and Biobe­hav­ioral Sci­ences
Brain Research Insti­tute, UCLA
Tel: 818–891-7711 ext.7581
Mobile: 818–891-8612

John Peev­er, PhD
Asso­ciate Pro­fes­sor, Sys­tems Neu­ro­bi­ol­o­gy Lab­o­ra­to­ry
Dept. Cell & Sys­tems Biol­o­gy, Uni­ver­si­ty of Toron­to
Tel: 416–946-5564
Mobile: 647–207-7920