Assessing nighttime vigilance through a three-letter cancellation task (3-LCT): effects of daytime sleep with temazepam or placebo

Nocturnal sleepiness is a common complaint suffered by night-shift workers, especially in conditions of an abrupt shift of the wake-sleep cycle. Alert ness management strategies can minimize the adverse effects of sleep loss a nd circadian rhythm desynchronization and promote optimal vigilance in oper ational settings. Within these strategies, one possibility is to use short periods of "prophylactic sleep" (before long periods of work), which can be facilitated by hypnotics. Vigilance can be evaluated by means of several t ests which, sometimes, imply procedures and devices not easily employable i n operational settings. In such conditions pencil and paper tests of vigila nce can be very useful in the assessment of attentional performance degrada tion due to sleep loss and/or inversion of the sleep-wake cycle. In this st udy we evaluated the sensitivity of a three Letter Cancellation Task (3-LCT ) in revealing nighttime variations of vigilance in a laboratory simulation of acute night shift, after a diurnal sleep with placebo (PLC) or temazepa m (TMZ). Nocturnal levels of vigilance were also assessed using the Mainten ance of Wakefulness Test (MWT) and the Multiple Sleep Latency Test (MSLT). All tests were administered four times at 2-h intervals during nighttime af ter a daytime sleep. Results show that the 3-LCT is sensitive to variations of vigilance occurring during a laboratory simulation of acute night shift . We also found some effects of TMZ, which in the first nocturnal session c aused a slowing down of visuoattentive performance. Nocturnal variations of vigilance detected through the S-LCT were similar to those revealed by mea ns of MSLT, while the ability to maintain wakefulness was substantially spa red during the night. (C) 1999 Elsevier Science Inc. All rights reserved.