The idea that memory consolidation is one function of sleep is quite old. So far, the evidence in favor of this notion is correlative: performance of a task that is learned before a good night's sleep improves the next morning. Reporting in Nature, Reto Huber et al. now show that areas of the brain that are relevant for learning experience local synaptic changes during sleep, and propose that these changes might benefit performance.

Credit: Reprinted from Nature

The researchers trained humans in a motor task known to activate mainly one region of the brain—the parietal lobe. They then measured electrical activity during sleep using 256 electrodes distributed over the skull, as shown here. Huber et al. were particularly interested in the slow wave activity (SWA) that appears during sleep. The longer we stay awake, the higher the pressure for sleep and the higher the proportion of SWA during the sleeping period. But the relationship between SWA and memory consolidation had not been explored, and the neuroanatomical specificity of the task provided these researchers with the ideal tool to address this question.

Huber et al. found that SWA increased over the parietal lobe (larger dots in the figure) in trained as compared to untrained subjects. What's more, the magnitude of this increase correlated with improved performance the next morning. These results indicate that the relationship between SWA and learning is tighter than previously believed. Although the evidence for a role of sleep in memory consolidation remains correlative, as far as correlations go, it doesn't get much better than this.