Paris, May 28, 2009

It really is best to sleep on it

The saying “Sleep on it” is turning out to be true. Researchers at the Laboratoire de physiologie de la perception et de l'action (LPPA, a CNRS/Collège de France research unit) and at the University of Amsterdam have shown that the brain replays the day's events while asleep. They have discovered that the information consolidated during sleep leads to the best decision-making while awake.
These results are published online on the website of the journal Nature Neuroscience.

While asleep, the neurons in our brain are constantly active at levels comparable to those observed while awake. This activity is of vital importance: during sleep, our brain unconsciously rearranges memories in order to stabilize them and ensure long term memory storage.


Researchers at the LPPA (CNRS/Collège de France) and the University of Amsterdam taught rats to find rewards in a maze and then studied the brains of the animals while they were asleep. The scientific team observed that the activity patterns of neurons during sleep resembled those of previous awake periods, while the rats were learning the task. But not all parts of the experience are replayed in the same manner in the brain. The neuron assemblies that were active at the moment of taking a decision and especially those active from the moment of understanding and learning the task were preferentially reactivated during sleep.  


This discovery suggests that not all memorized information is consolidated in the same way and that only the most relevant information for behavior is stabilized. This work represents a significant advance in our understanding of memory in the brain and the manner in which it encodes information. This approach is needed to improve our knowledge in cases of age-related neuronal degeneration such as Alzheimer's disease, in which memory is considerably disrupted.


La nuit porte conseil

© Peyrache et al.

Reactivation during sleep. The electrical activity of the brain has a tendency to oscillate differently depending on the waking or sleeping states. During a specific sleep phase, known as slow wave sleep, the oscillations are higher in the lower frequencies (the other phase being REM sleep). The colors of the image represent the strength of the electrical signal in each of the frequencies (red: strong, blue: weak) and enable the periods of slow wave sleep (indicated by black bars above) to be clearly distinguished during a long period of inactivity of the animal, which here lasts more than 25 minutes. The superimposed white curve shows the times when a cell assembly formed while awake is replayed, corresponding to the peaks towards the top of the curve. These peaks are only visible during slow wave sleep.


Replay of rule-learning related neural patterns in the prefrontal cortex during sleep, A. Peyrache, M. Khamassi, K. Benchenane, S. I. Wiener, F. P. Battaglia, Nature Neuroscience online 31 May 2009.


Adrien Peyrache l T 01 44 27 16 30 l
Sidney Wiener l T 01 44 27 16 21 l

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