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Lack of sleep causes hippocampus to shrink

26 January 2012

A good night’s sleep is hard to come by in our current 24-hour society. However, a lack of sleep can have a very damaging effect on the brain. The Groningen neurobiologist Peter Meerlo and his colleague Arianna Novati have shown that the hippocampus, the part of the brain involved in learning, memory and emotions, even shrinks in rats with chronic sleep deprivation.

Peter Meerlo and Arianna Novati investigated the brains of laboratory rats who were allowed only four hours of sleep a day, whereas the animals usually sleep for more than ten. In previous research, Meerlo already discovered that a week of too little sleep had serious consequences for a rat brain – the serotonin system, involved in stress and emotions, was disrupted and became much less sensitive to the neurotransmitter serotonin.

Smaller hippocampus

A month of sleep deprivation turned out to have an effect on the rat brain itself too. Meerlo and Novati discovered that changes then occur in the structure of the brain. Meerlo: ‘The hippocampus in rats who have had too little sleep for a month turn out to have become about ten percent smaller. This means that the hippocampus – that part of the brain involved in learning, memory and emotions – is very sensitive to disruption such as sleep deprivation.’


A reduction in the size of the hippocampus could influence learning performance and mood. Meerlo: ‘Patients with depression also show a reduction in the size of the hippocampus and a disrupted serotonin system. These results thus confirm that a sleep problem is not only one of the symptoms of depression, but may also be a cause.’


Meerlo does not yet know if the hippocampus shrinkage is reversible: ‘That is one of the most important questions in our follow-up research. Although we know that there is shrinkage, the mechanism is not yet clear. Maybe the brain cells die off, or reduce the production of new cells – but the cells present could also just be decreasing in volume.’

24-hour society

A lack of sleep is a phenomenon that is becoming more common in Western society. Not only adults on shift work or with a lot of work pressure suffer from it, but also children who watch television or surf the internet into the wee small hours and have to be up early for school the next morning. The research results mean that we must take sleep more seriously in the current 24-hour society, according to Meerlo: ‘We spend a lot of time on eating healthily, not smoking and getting enough exercise but we’re not that bothered about getting enough sleep. And sleep should definitely be on that list of good habits.’

Curriculum Vitae

Peter Meerlo (1966) graduated as a biologist from the University of Groningen in 1991, and gained a PhD in 1997 in the biology of the brain and behaviour. He then worked in Chicago as a postdoc, returning to Groningen in 2002. Meerlo, who has a Vidi grant from NWO, is a joint supervisor of Arianna Novati (Italy, 1979), who will be awarded a PhD by the University of Groningen on 3 February 2012 for this research. The title of her thesis is Sleep loss, brain vulnerability and psychopathology: experimental studies on the neurobiological consequences of chronic sleep restriction in rats.

Note for the press

For more information: Dr Peter Meerlo, e-mail: p.meerlo, tel.: +31 (0)50 363 2334.

Last modified:13 March 2020 01.51 a.m.
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