What does it mean that sleep preferentially consolidates "future-relevant" information?

The brain consolidates more strongly what it has tagged as important — and simply expecting a test tomorrow is enough to tag material.

Wilhelm et al. found that participants who were told they would be tested the next day showed stronger sleep-dependent consolidation of the material than those who didn't expect a test — even though everyone slept the same. The expectation acted as a relevance tag that the sleeping brain then prioritised.

The practical lesson: sleep isn't an indiscriminate archive. Signalling to yourself that material matters — by planning to self-test, or genuinely caring about it — recruits sleep's consolidation machinery toward that material. Sleep amplifies what you flagged as worth keeping.