Gender and age differences in psychomotor vigilance performance under differential sleep pressure conditions.
The effects of sleep pressure and circadian phase on neurobehavioral function can be sensitively measured with the psychomotor vigilance task (PVT). We compared PVT performance in 16 young (8 men and 8 women, 20-31 years) and 16 elderly healthy subjects (8 men and 8 women, 57-74 years) during a 40-h sleep deprivation (SD, high sleep pressure) and a 40-h multiple nap protocol (NAP, low sleep pressure) under dim light and constant posture conditions in a balanced crossover design. Independent of age and sleep pressure conditions, women exhibited significantly slower reaction times (RTs) than men. This effect became more apparent with increasing time elapsed into both the 40-h NAP and SD protocol. However, women tended to have fewer premature key presses than men. Independent of gender, the elderly showed slower RTs than the young in the NAP protocol during the biological day (8-24 h) but not during the biological night (24-8 h). In the SD protocol, they had also significantly slower RTs but only during the first 16 h under low to moderate levels of sleep pressure conditions. The relative PVT performance decline after SD was significantly less pronounced in the elderly than in the young, so that both age groups exhibited similar performance decrements after 16 h into the SD protocol. Thus, nighttime- and sleep pressure-related RT slowing in the young "makes them old", or the elderly are less susceptible to circadian and wake-dependent PVT performance decrements. We interpret the gender effect as a different strategy in women when performing the PVT, although the instructions to be 'as fast as possible' were identical. Not only sleepiness and circadian phase, but also age and gender are major factors that may contribute to attentional failures in extended work shifts and during nighttime work shifts.