UPCAT Reading Comprehension practice question 26: According to the passage, what happens in the hippocampus during deep sleep?

The old view of sleep treated it as a pause, a period in which the brain simply idled while the body repaired itself. Recordings of neural activity have made that description untenable. During deep sleep, the hippocampus replays sequences of activity from the day at accelerated speed, and the cortex receives them. Over successive nights, memories that begin as fragile hippocampal traces are gradually stabilized in cortical networks.

This process is selective. Not everything encoded during waking hours is retained, and the sorting appears to favor material the brain has been given reason to treat as important, whether by emotional weight or by a signal that it will be needed again.

The practical implication runs against a common student habit. A single long night of study before an examination allows almost no consolidation, because consolidation requires sleep that the night has been spent avoiding. The same total hours distributed across a week, each session followed by ordinary rest, produce markedly better retention.

Sleep, on this account, is not the interval between periods of learning. It is one of the periods of learning, and the one during which the sorting actually happens.