Tokley, Melanie Joy (2009) Sleep inertia and alcohol impairment in young adults: neurocognitive effects and interactions Implications for fire escape behaviours. Other Degree thesis, Victoria University.

Abstract

Alcohol intoxication is known to considerably increase the probability of death from fire across the lifespan, to the extent that it has been isolated as the single most significant risk factor. The study investigated the combined effects of sleep inertia and alcohol impairment on fire emergency-relevant cognitive performance indicators in a young adult population. Mental tracking, visual scanning, psychomotor speed, working memory and sustained, selective, and divided attention functions were assessed for performance decrements and reference to speed-accuracy trade-off effects. Participants were 24 young adults (18-26 years) who participated in a repeated-measures study over 2 nonconsecutive nights; 1 night with alcohol administration and 1 ‘sober’ night. During the alcohol administration night, 10-minute testing blocks occurred under (1) baseline sober and (2) baseline 0.05 blood alcohol concentration (BAC) conditions. Subsequently, subjects were awoken from stage 4 sleep and assessed in two consecutive 10-minute blocks (3) and (4). Self-reports of sleepiness and clearheadedness were also taken. The same procedure was used during the sober night (with condition (2) excluded). All cognitive functions assessed showed an alcohol effect (i.e., decrements between sober baseline (1) and conditions of alcohol (2)), and an even larger sleep inertia effect (i.e., greater decrements between sober baseline (1) and conditions of sleep inertia alone (3) and (4)). Sleep inertia selectively affected performance speed on the working memory task, whilst performance accuracy on this task was affected by conditions of alcohol impairment only. When the sober and alcohol nights were compared, there was no combined or synergistic interaction between sleep inertia and alcohol impairment on the cognitive tasks or subjective measures during the first 10 minutes of sleep inertia. Conditions of combined sleep inertia and alcohol impairment produced cognitiveperformance decrements that were greater than those produced by alcohol administrationalone, but not those produced by sleep inertia alone. Indeed, sleep inertia effectsappeared to ‘override’ alcohol effects. At 10-20 minutes post-awakening, however, sleepinertia effects began to dissipate, thus ‘unmasking’ alcohol effects on some tasks,including accuracy of working memory performance, selective/sustained attention and subjective sleepiness. Divided attention performance demonstrated a complex and unpredictable pattern at 10-20 minutes post-awakening whereby performance under conditions of sleep inertia and alcohol intoxication combined became significantly worse than either condition alone, indicating that alcohol effects were also possibly being unmasked for this measure. Other measures (speed of working memory performance and subjective clearheadedness) showed no difference between conditions at 10-20 minutes post-awakening. The results suggest that (1) moderate alcohol impairment and sleep inertia do not combine to produce further decrements in neurocognitive functioning than those caused by the effects of alcohol or sleep inertia alone and (2) sleep inertia poses a greater risk to fire emergency escape than moderate alcohol impairment. Moreover this data suggests that when awoken abruptly in an emergency situation, prior alcohol consumption to 0.05 BAC will not further impede cognitive functioning that is already compromised by a state of sleep inertia. The study considers the importance of the arousing effects of task complexity, the BAC curve (particularly the descending limb), and speed-accuracy trade-off effects in predicting the effects of sleep inertia and alcohol on cognitive performance.

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