It turns out that nodding off in class may not be such a bad idea after all, as a new study has shown that going to sleep shortly after learning new material is the best way to remember it.

看来在课堂上打瞌睡也许并不是坏事。一项新研究显示，学完新知识后马上打个小盹是最佳的记忆方法。

According to US lead author Jessica Payne, a psychologist at the University of Notre Dame¹ in Indiana, nodding off after learning something new is like 'telling' the sleeping brain what to retain.

Along with colleagues, she studied 207 students who habitually² slept for at least six hours per night.

Participants were randomly³ assigned to study declarative, semantically related or unrelated word pairs at 9am or 9pm, and returned for testing 30 minutes, 12 hours or 24 hours later.

Declarative memory refers to the ability to consciously remember facts and events, and can be broken down into episodic memory (memory for events) and semantic（语义的） memory (memory for facts about the world).

People routinely use both types of memory every day – recalling where we parked today or learning how a colleague prefers to be addressed.

At the 12-hour retest, memory overall was superior following a night of sleep compared to a day of wakefulness.

At the 24-hour retest, with all subjects having received both a full night of sleep and a full day of wakefulness, subjects' memories were superior when sleep occurred shortly after learning, rather than following a full day of wakefulness.

'Our study confirms that sleeping directly after learning something new is beneficial for memory. What's novel about this study is that we tried to shine light on sleep's influence on both types of declarative memory by studying semantically unrelated and related word pairs,' Payne said.

'Since we found that sleeping soon after learning benefited both types of memory, this means that it would be a good thing to rehearse（排练，预演） any information you need to remember just prior to going to bed. In some sense, you may be "telling" the sleeping brain what to consolidate⁴（巩固，加强） .'

Results of the study were published on March 22 in PLOS One.