Electrophysiological correlates of cognition improve with nap during sleep deprivation

The efficacy of a 30-min nap as a countermeasure in the reduction of cognitive decline following 24 h of sleep deprivation (SD) on subjective sleepiness scales, event-related potential (ERP) P300, and contingent negative variation (CNV) was evaluated. The experiment was performed in three sessions on different days between 7 and 8 a.m. on nine normal, healthy males, of age 25-30 years: Session 1. Baseline recordings; Session 2, after one night's total sleep deprivation, and; Session 3, after 1 week of Session 1, following one night's sleep deprivation along with a 30-min nap opportunity between 1.00 and 3.00 a.m. Subjective sleepiness scores increased after SD as compared to baseline, but reduced significantly after nap (P < 0.05). There was an increase in P3 peak latency of ERP following SD (16%, P < 0.01), which was reduced with nap (10.7%, P < 0.05).There was an increase in CNV M1 peak latency after SD (18%) which decreased with the use of nap (12.5%) (P < 0.01). The CNV reaction time increased following SD (39.3%) and decreased with the use of nap (24%) (P < 0.01). No significant effects on ERP N1, P1, N2 latencies, P2 and P3 amplitudes and CNV N1, P3, M2 peak latencies and M1, and M2 amplitudes were observed. It was concluded that a 30-min nap, between 1.00 and 3.00 a.m. during night SD, reduces the cognitive decline following 24 h of SD in terms of its electro-physiological correlates. The study is of applied value in optimization of cognitive performance in professions demanding night work schedules.