BPS Research Digest: Why teens should have th...

While you sleep your brain learns. Research with rats has shown how they rehearse maze-routes in their brains whilst they're dozing. And human research has demonstrated that learned material is better recalled after a sound sleep as opposed to a disturbed night. But what hasn't been looked at before now is the optimum time to leave between learning and sleeping.

A team led by Johannes Holz has done just that, finding that "procedural learning" (practice at the kind of skill that you do, rather than talk about) is more effective right before sleep. Learning factual material, by contrast, (dependent on "declarative memory"), was found to be more effective when done in the afternoon, seven and a half hours before sleep, although the evidence for this was less convincing and should be treated with caution.

The researchers recruited 50 teenage girls (aged 16-17) to learn a series of word pairs and a finger-tapping task, either at 3pm in the afternoon or 9pm at night. The performance level of the afternoon and night groups was equivalent at the end of these initial learning tasks.

With the tapping task, it was the girls who learned right before sleep who showed the greatest gains in performance when they were re-tested after 24 hours and again 7 days later. Holz and his colleagues can't be sure why procedural learning is more effective just before sleep, but they think it probably has to do with the effect of sleep on protein synthesis and gene expression.

In contrast to the tapping task, performance on the word pairs after 24 hours was better in the afternoon-learning group. At the 7 day word-pairs test there was no difference in afternoon or evening learners. The fact that declarative learning was more effective in the afternoon suggests that this type of hippocampus-dependent memory has a different time course from procedural learning.

The findings, though preliminary, have obvious practical implications. "We propose that declarative memories, such as vocabulary words, should be studied in the afternoon and motor skills, like playing soccer or piano, should be trained in the late evening," the researchers said. "Most parents among us would have preferred the opposite results."