Habitual napping and performance on the Trail Making Test

Neuropsychologists typically administer psychometrics without formal recognition of an individual’s sleep/wake history, despite a voluminous experimental literature extending back over 40 years suggesting that sleep at night effects daytime performance (Van Dongen et al., 2004; Wilkinson, 1961). Recently, a large epidemiologic study of nearly 5000 individuals noted subjectively reported sleep duration of sleep on the night immediately preceding neuropsychological testing predicted performance on tests of simple reaction time and new learning (Krieg et al., 2001). In this report, we note relationships between the subjective report of habitual napping and performance on a widely used, paper and pencil neuropsychological test, the Trail Making Test (TMT) (Reitan and Davison, 1974). Subjects in this study were 974 individuals (712 men, 262 women) drawn from the Western Collaborative Group Study (WCGS), a large, prospectively followed epidemiological population residing in Northern California. All subjects gave voluntary informed consent before participation. Complete description of the study population has been given elsewhere (Rosenman et al., 1970; Swan et al., 1998). The mean age of the follow-up population at the time of present data collection was 75.7 years (SD 1⁄4 4.0) for men and 71.0 (SD 1⁄4 5.2) for women. We defined dementia by a score of <1.52 on the Iowa Battery for Mental Decline (Eslinger et al., 1985). The TMT parts A and B (TMT-A, TMT-B) was administered by trained examiners using standardized test administration. Time of day was not controlled. Depression was examined with the Center for Epidemiologic Studies Depression Scale (CES-D) (Radloff, 1977). We characterized napping frequency with the following question: How often do you take naps during the day? This could be answered: 1 1⁄4 never, 2 1⁄4 less than once a week, 3 1⁄4 one to two times a week, 4 1⁄4 three to five times a week, or 5 1⁄4 daily. Subjects were instructed to use a time frame of the last 6 months in answering this question. The question was administered as a part of a large array of health-related questions routinely collected in the WCGS (Swan et al., 1998). Age and CES-D adjusted TMT-B times are shown in Table 1 for both the entire sample and the non-demented sample. TMT-A results did not demonstrate significant differences by napping frequency. Both age and depression were significant covariates of napping (both P < 0.001), however, TMT-B performances showed a significant decrease with greater likelihood of napping. The difference between the highest and lowest napping categories was 11–12 s, and this did not vary by gross level of cognitive impairment (Iowa score). Napping frequency was unrelated to educational level. As would be expected, TMT-B times (in seconds) for those individuals with Iowa scores below 1.52 were significantly longer than for those with Iowa scores greater than or equal to 1.52 [120.5 (47.1) versus 95.3 (33.3), t 1⁄4 5.53, P < 0.0001]. The TMT is one of the most widely used components of many neuropsychological test batteries. It is typically considered to be an effective test to assess visual scanning with a motor component (Lezak, 1995), visual attention and information processing (Mitrushina et al., 1999), and visual-perceptual performance (Spreen and Strauss, 1998). Performance on part B may even, to some extent, serve as a rough marker of frontal lobe function (Green, 2000), and it has shown a robust genetic etiology (Swan and Carmelli, 2002). It is a simple test, lasting several minutes at most, and therefore might be expected to be relatively unaffected by characteristic levels of daytime sleepiness. Effective neuropsychological testing technique is usually considered to mitigate the influence of tiredness by offering frequent breaks, maintaining patient cooperation, and sustaining motivation. Such skills are considered part and parcel of conducting detailed psychometrics, which can easily total several hours in duration, depending upon the number of tests employed. Just as inquiring about the length of sleep the prior night seems to have been an issue heretofore unrecognized in making such assessments (Krieg et al., 2001), routine inquiry as to frequency of daytime napping, particularly in an elderly population, may be of value in accounting for performance. Of note is that other studies using a very brief (5-min) paper and pencil test (e.g. Letter Cancellation Task) have also shown sensitivity to an individual’s sleep history (Casagrande et al., 1997). Potential limitations in our data must be acknowledged. Reported napping may relate imperfectly to objective measures of daytime sleepiness or alertness. Moreover, although we Correspondence: Donald L. Bliwise, PhD, Program in Sleep, Aging and Chronobiology, Department of Neurology, Emory University Medical School, Wesley Woods Center, 1841 Clifton Road, Atlanta, GA 30329, USA. Tel. : +1 404 728 4750; fax: +1 404 728 4756; e-mail: dbliwis@emory.edu J. Sleep Res. (2005) 14, 209–210