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A study conducted by sleep researchers at Northwestern University has shown that when animals are partially sleep deprived over consecutive days, they no longer attempt to catch up on sleep despite an accumulating sleep deficit.

The study suggests that repeated partial sleep loss negatively affects an animal¡¯s ability to compensate for lost sleep, and that the body responds differently to chronic sleep loss than it does to acute sleep loss.

Published in the Proceedings of the National Academy of Sciences (PNAS), these findings shed light on a problem prevalent in industrialized nations with 24/7 societies, such as the US, where people get nearly an hour less sleep a night than they did 40 years ago.

¡°We now know that chronic lack of sleep has an effect on how an animal sleeps,¡± said lead study author Fred W. Turek, Professor of Neurobiology and Physiology, whose paper has been published in the Proceedings of the National Academy of Sciences (PNAS).

¡°The animals are getting by on less sleep but they do not try and catch up. The ability to compensate for lost sleep is itself lost, which is damaging both physically and mentally,¡± he added.

During the study, animals were kept awake for 20 hours per day followed by a four-hour sleep opportunity, over five consecutive days. The researchers monitored their brain wave and muscle activity patterns in order to precisely quantify sleep-wake patterns.

The animals compensated for the sleep loss by increasing the depth of sleep after the first day, which is indicative of a homeostatic response. But on the subsequent days of sleep loss, they failed to generate this compensatory response, and did not sleep any more deeply or any longer than they did under non-sleep deprived conditions.

At the end of the study, the animals were given three full days to sleep as much as they wanted. It was observed that they seldom recovered the sleep they had been deprived of during the five consecutive days in the immediate past.

The findings support the recent human studies that suggested that chronic partial sleep loss of even two to three hours per night could have detrimental effects on the body, leading to impairments in cognitive performance, as well as cardiovascular, immune and endocrine functions. Sleep-restricted people also reported not feeling sleepy, even though their performance on tasks declined.

¡°Even though animals and humans may be able to adapt their sleep system to deal with repeated sleep restriction conditions, there could be negative consequences when this pattern is maintained over a long period of time,¡± said Turek.

¡°This brings us back to the idea that repeated partial sleep restriction in humans has been linked to metabolic dysfunction and cardiovascular disease,¡± added the researcher.