0106 Unitization Improves Memory for Associations during Sleep Deprivation

Abstract

Abstract Introduction Total sleep deprivation (TSD) impairs binding, i.e., the ability to form new associations. Unitization – when separate memory items are learned as a single unit (e.g., combining two words into a novel compound word) – reduces the need for binding. Unitization mitigates impaired memory for associations in amnesiacs, but whether it offsets binding problems from TSD is unknown. Methods N=23 healthy adults (ages 19-35, 8 women) participated in an ongoing, double-blind, 4-day/3-night in-laboratory study with a 10h baseline sleep opportunity, 38h TSD, and a 10h recovery sleep opportunity. During TSD, participants were randomized to four administrations of caffeine (200mg), modafinil (alternating between 200mg and 0mg), or placebo at 4h intervals beginning at 01:00. They completed a unitization task at 14:45 on day 2 (baseline, session 1), day 3 (TSD, session 2), and day 4 (recovery, session 3). The task began with a study phase where participants studied 60 pairs of words that were presented individually (e.g., “penny” and “tower”) or as new, unitized words (e.g., “pennytower”) (50% each). Afterward, in the test phase, participants indicated whether 60 presented pairs of individual words were old (presented together at study) or new (recombined into new pairs) (50% each). Results Repeated-measures ANOVA revealed significant effects of study pair type (individual or unitized), session (1–3), and their interaction (p<0.05). Performance did not differ by pair type in session 1 (p=0.46), and performance for pairs of individual words did not change across sessions (p=0.34). However, performance on unitized word pairs improved across sessions (p=0.003), and unitized word pairs were recognized better than individual word pairs in sessions 2 and 3 (p<0.05). Conclusion Across sessions, participants benefitted from practice on unitized word pairs, such that performance improved even during TSD. Although potentially partly attributable to drug condition (to which investigators are still blinded), no such practice effect was seen for word pairs studied individually. Whether this dissociation implies that unitization bypasses the need for binding and thus lessens the impact of TSD requires further investigation. Regardless, unitization may mitigate performance impairment from sleep loss in settings that require forming novel associations, such as eyewitness identifications. Support (If Any) USAMRDC W81XWH-18-1-0100 and CDMRP W81XWH-20-1-0442.