Time-on-task impairment of psychomotor vigilance is affected by mild skin warming and changes with aging and insomnia.

STUDY
OBJECTIVES: To investigate the effect of mild manipulations of core and skin temperature on psychomotor vigilance (PVT) in young adults, elderly, and elderly insomniacs.
DESIGN: 432 PVTs were obtained during a 2-day semi-constant routine protocol, while differentially manipulating core and skin temperatures within a comfortable thermoneutral range.
SETTING: Sleep laboratory of the Netherlands Institute for Neuroscience. PATIENTS OR PARTICIPANTS: Groups of 8 sex-matched young adults (27.0 +/- 2.4 years, mean +/- s.e.m.), elderly (65.8 +/- 2.8 years), and insomniacs (59.1 +/-1.9 years). MEASUREMENTS AND
RESULTS: During the 7-minute PVTs, response speed typically declined with increasing time-on-task. Proximal skin warming by only +/- 0.6 degrees C accelerated this decline by 67% (P = 0.05) in young adults and by 50% (P < 0.05) in elderly subjects. In elderly insomniacs, proximal warming slowed down the mean response speed already from the onset of the task (3% level drop, P < 0.001). Response speed tended to decrease with age (P < 0.10), reaching significance only in elderly insomniacs (P < 0.05). Speed decrements occurred mostly towards the end of the time-on-task in young adults; earlier and more gradually in elderly without sleep complaints; and very early and in a pronounced fashion in insomniacs. Interestingly, the worsening by warming followed the time pattern already present within each group.
CONCLUSIONS: The results are compatible with the hypothesis that the endogenous circadian variation of skin temperature could modulate vigilance regulating brain areas and thus contribute to the circadian rhythm in vigilance. Minute-by-minute PVT analyses revealed effects of age and insomnia not previously disclosed in studies applying time-point aggregation. Our data indicate that "age-related cognitive slowing" may result, in part, from age-related sleep problems.