MCAT Practice Test 3

Sleep and Interference in Declarative Memory

¹Researchers examined whether sleep protects newly learned declarative memories against later interference. Prior work suggests that during slow-wave sleep (SWS), recently encoded memories are reactivated and stabilized, a process called sleep-dependent consolidation. If consolidation strengthens memories, the benefit of sleep may be most visible when those memories are later challenged.

²Ninety-six undergraduates (ages 18–24) were randomly assigned to four groups (n = 24) in a 2 × 2 design. All participants learned 40 word pairs (A–B pairs, such as candle–river) to a criterion of 70% correct. Sleep groups learned the pairs at 9:00 p.m. and slept in the laboratory while polysomnography recorded sleep stages; wake groups learned at 9:00 a.m. and continued their normal daytime activities. After a 12-hour interval, half of each group (interference condition) learned a second list in which the same cue words were paired with new responses (A–C pairs, such as candle–ladder) immediately before a cued-recall test of the original A–B pairs. The other half (no-interference condition) rested for 10 minutes before the same test. Two additional groups (n = 16 each) learned the A–B pairs at either 9:00 a.m. or 9:00 p.m. and were tested after only 20 minutes.

³Results are shown in Figure 1. The Sleep × Interference interaction was significant (p < 0.01), and the standard error of the mean was about 3 percentage points in every group. The 20-minute groups recalled 86% (morning) and 85% (evening) of the pairs, a nonsignificant difference. Within the sleep groups, minutes of SWS correlated positively with A–B recall (r = 0.45, p < 0.05), whereas minutes of REM sleep were unrelated to recall.

⁴In a follow-up study, a new sample completed the same sleep and wake procedures but gave a stressful 5-minute public speech immediately before the recall test. Salivary cortisol rose by about 60%, and A–B recall fell in both the sleep and wake groups relative to the values in Figure 1. The authors concluded that sleep stabilizes memories against interference but that retrieval remains vulnerable to acute stress.