The influence of a 1 h nap on performance overnight

The effect on performance overnight of a 1 h nap taken at 0200 h was studied in six young female subjects. The subjects completed three schedules, including one with a nap and two without a nap, during which either a placebo or 300 mg caffeine was ingested at 2315 h. Performance was measured from 1700 h in the evening until 1030 h the next morning. Caffeine improved performance overnight on almost all tasks compared with placebo. The nap had some limited beneficial effect compared with placebo, but most tasks remained impaired.