Load a hard problem before sleep

Review the problem just before bed so overnight consolidation can work on it.

Why it works

Sleep is the most reliable diffuse-mode period. During NREM and REM, the hippocampus replays material from the day and the neocortex integrates it into longer-term patterns. Deliberately reviewing the problem — especially its stuck point — before sleep gives the consolidation process a specific target and increases the likelihood of insight on waking.

How to do it

1. In the last 10 minutes before bed, read or write what you are trying to solve — no screens.
2. Do not try to solve it; just review the material and the question.
3. Keep a notepad by the bed and write down what comes on waking, before other inputs crowd it out.

Evidence

Sleep consolidation research consistently shows that targeted pre-sleep review improves next-day recall and problem solving on trained material. The "targeted memory reactivation" paradigm supports deliberate loading of specific content for consolidation. (observational)

Walker's "Why We Sleep" has been criticized for selective citation and overstated claims in some areas; the underlying consolidation research is sound but more nuanced than the popular account.

Sources

• Walker (2017), Why We Sleep — summary of sleep consolidation and REM insight research

Common mistake

Reviewing by scrolling through notes on a phone — the blue light, the cognitive activation, and the feed temptation all interfere with the sleep transition the practice depends on.