Arousal components which differentiate the MWT from the MSLT

The purpose of this study was to determine the relative contribution of the instruction to maintain wakefulness versus posture change as major components determining sleep latency in the MWT as compared to the MSLT.

After adaptation, subjects spent 3 nights and the following days in the laboratory. On each day, Ss had eight sleep latency measurements including four sleep latency tests from two of the following conditions: Lay down and Sleep (MSLT); Lay down and stay Awake; Sit up and Sleep; Sit up and stay Awake (MWT); and sit in a chair in front of a Computer and stay awake.

Participants were 14 young adult normal sleepers.

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Significant differences in sleep latency were found for each condition with respect to all of the others except that the Computer condition did not differ from the Sit-Awake condition. Means for conditions were: Lay-Sleep -11.1 minutes; Sit-Sleep -17.7 minutes; Lay-Awake - 21.7 minutes; Sit-Awake - 29.0 minutes; Computer - 30.1 minutes. Correlations between conditions declined as subjects sat up.

The MWT differs from the MSLT by taking advantage of the arousal system (motivation and posture) to maintain alertness (i.e., increase sleep latency). These arousal effects are additive. MSLT results may not always correlate well with MWT results because the MWT measures the combined effects of the sleep and arousal systems while the MSLT, in ideal situations, measures only sleepiness.