Chronic insomnia and performance in a 24-h constant routine study MICHAEL VARKEVISSER 1 and GERARD A. KERKHOF 1,2 1 Department of Psychology, University of Amsterdam, Amsterdam and 2 Centre for Sleep and Wake Disorders, MCH Westeinde, The Hague, The Netherlands Accepted in revised form 21 June 2004; received 4 September 2003 SUMMARY Insomniacs report daytime functioning problems, but studies of neurobehavioral functioning in insomniacs have shown little objective evidence of impairment. In addition, very little is known about the influence of the circadian clock on performance in chronic insomniacs. In the present study, we investigated whether chronic insomnia is associated with an overall performance deficit, and what the effect is of circadian rhythmicity, under strictly controlled laboratory conditions. A 24-h experiment was carried out under constant routine conditions. Psychomotor performance, body temperature, and subjective functioning of 11 insomniacs and 13 healthy subjects were assessed. The insomniacs showed significant overall performance impairments in vigilance, working memory, and motor control. In addition, body temperature, performance and subjective functioning showed a circadian pattern similar to healthy subjects, with trough values in the late night/early morning and peak values in the early evening. Self-reported functioning among the insomniacs indicated mood disturbances, concentration problems, elevated fatigue and elevated sleepiness. The results indicated that chronic insomnia is associated with a substantial lowering of the 24-h level of performance and subjective functioning, irrespective of the type of task and/or the particular parameter, and without differential effects of circadian rhythmicity. Apparently, chronic insomnia has a negative impact upon performance as measured under strictly controlled, unmasked conditions. keywords chronic insomnia, circadian rhythm, constant routine, performance, subjective functioning INTRODUCTION Disrupted sleep, generally demonstrated in studies of individ- uals suffering from chronic insomnia, is expected to have a detrimental effect on daytime functioning. Indeed, most insomniacs report problems in their functioning, i.e. deterior- ation of mood and concentration, the occurrence of anxiety, etc., which, to their belief, have negative daytime consequences (Chambers and Keller, 1993). Several laboratory studies have investigated the consequences of chronic insomnia on daytime performance. Surprisingly, most studies found no clear evidence of performance impairments during the day (Adams et al., 1986; Hauri, 1997; Schneider-Helmert, 1987). Similarly, when asked about their functioning at a specific time, e.g. before or after bedtime, no differences were found between insomniacs and normal sleepers (Bonnet and Arand, 1998). This absence of a difference in time-specific reports of daytime functioning, as contrasted to global reports, may reflect a ÔtraitÕ component of dysfunctional beliefs about the impact of disturbed sleep in insomniacs (Hart et al., 1995). On the basis of such results it has been concluded that either insomnia does not impair objective daytime functioning, or that it affects only specific aspects of performance, such as vigilance and imme- diate memory (Fulda and Schulz, 2001; Schneider-Helmert, 1987). Most laboratory studies investigating insomnia in relation to daytime functioning did not take account of factors such as postural changes, food intake, light exposure and social interactions, which are known to have a profound impact on daytime behavior. Insomniacs may profit from these factors, Correspondence: Michael Varkevisser, Department of Psychology, University of Amsterdam, Roetersstraat 15, 1018 WB Amsterdam, The Netherlands. Tel.: (+31) 70 3302841; fax: (+31) 20 639 1656; e-mail: m.varkevisser@uva.nl J. Sleep Res. (2005) 14, 49–59 Ó 2005 European Sleep Research Society 49