Every day, new brain cells (neurons) are born in the brains of adult mammals, a process called neurogenesis (neuro = neurons, genesis = birth).  These newborn cells appear particularly in the hippocampus – a brain area that is important for new memory formation.   Over the next few weeks, many of these newborn cells die off again.  But studies show that, if a rat has been exercising or has been exposed to new learning, more of the newborn cells survive.  The rate of survival of these new cells also depends on sleep.

As we sleep, we (like rats) cycle through several “stages,” including rapid-eye movement (REM) sleep, which is believed to be when we dream, and several kinds of non-REM sleep.

A recent study has suggested that REM is particularly important for neurogenesis in the hippocampus.  One group of rats were given four days of REM deprivation, by putting the rats in a small chamber where the floor was a treadmill that automatically activated whenever the rats entered REM sleep – forcing them to step forward to avoid being carried into the wall of the chamber.  (Non-REM sleep didn’t activate the treadmill.) For comparison, a group of control rats were placed in the same type of chamber, but treadmill activation was unrelated to sleep cycle.

The REM-deprived rats showed much less neurogenesis than controls. Both groups showed similar amounts of total sleep, and similar levels of stress hormones, indicating that the stress of being periodically awoken was similar for the REM-deprived and control rats. This study therefore suggests that REM sleep is particularly important for the birth and survival of new neurons in the adult brain.

There are two important implications of this study.  The first is that it adds to a growing literature suggesting that relatively short-term periods of sleep deprivation (equivalent to a few nights’ insomnia or intentional wakefulness) can significantly affect the brain.  This is a cautionary finding for those of us who routinely don’t get a full night’s sleep.

The second implication is that not all sleep is equal.  This study also adds to a growing literature suggesting that REM sleep has some special functions, particularly contributing to learning and memory.  Many medications, including some over-the-counter sleeping aids, disrupt REM sleep.  If REM sleep is indeed important for neurogenesis, then disrupting REM may disrupt neurogenesis – which might in turn have consequences for a person’s learning and memory abilities.

Further Reading:

R. Guzman-Marin et al. (2008). Rapid eye movement sleep deprivation contributes to reduction of neurogenesis in the hippocampal dentate gyrus of the adult rat. Sleep, 31(2):167-175.

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