0259 SLEEP DEPRIVATION EFFECTS ON THE DIGIT SYMBOL SUBSTITUTION TEST: GENERAL COGNITIVE SLOWING OR WAKE STATE INSTABILITY?

Sleep deprivation (SD) causes wake state instability, which amplifies variability in reaction times (RTs), skews the RT distribution, and increases the frequency of lapsing on the Psychomotor Vigilance Test (PVT). SD also causes various other effects on a range of cognitive performance tasks. Any shared underlying mechanisms for these effects have been difficult to demonstrate due to heterogeneity of task characteristics and outcome measures. Here we used a computerized Digit Symbol Substitution Test (DSST), which involves matching symbols to digits based on a 9-number key. Cognitive throughput (number of correct responses) on the DSST is used as a measure of cognitive processing speed, in both aging and sleep research. SD reduces cognitive throughput on the DSST, suggesting that SD slows cognitive processing speed. We investigated whether RT distributions on the DSST reflect general cognitive slowing, or rather wake state instability. N=56 healthy adults (ages 22–37, 29 females) completed a 4-day/3-night in-laboratory study, randomized with a 2:1 ratio to a total SD (TSD) condition or a well-rested control condition. The TSD condition (n=37) had 10h sleep opportunities (22:00-08:00) on the first and last nights, with 38h TSD between; the control condition (n=19) had 10h sleep opportunities each of the three nights. A 10min, computer-paced PVT and a 4min, subject-paced DSST were administered twice before TSD, twice during TSD, and once following recovery. Lapses were defined as RTs≥2000ms on the DSST and RTs≥500ms on the PVT. TSD reduced cognitive throughput on the DSST (p<0.001). TSD reduced mean response speed (1/RT) on the DSST (p<0.001) and PVT (p<0.001). However, TSD also increased the number of lapses on the DSST (p<0.001) and PVT (p<0.001). Furthermore, TSD skewed the RT distribution for both tasks. A hallmark effect of SD on the PVT is wake state instability. Despite considerable differences in task characteristics, we observed the same phenomenon on the DSST. It thus appears that reduced cognitive throughput on the DSST during SD reflects wake state instability. Office of Naval Research grant N00014-13-1-0302.