Sleepiness contributes to between 20 and 30% of all heavy vehicle accidents throughout the world each year. Professional drivers are particularly susceptible to the effects of sleepiness, due to chronic or acute sleep deprivation, time-on-task effects, driving at circadian low points, and increased daytime sleepiness resulting from sleep disorders. Population surveys of heavy vehicle drivers indicates that a small proportion of drivers use pharmaceutical means in order to help maintain alertness during long-haul trips. Despite the known benefits of amphetamine-type stimulants on reducing fatigue and sleepiness, epidemiological evidence suggests that a large percentage of fatally injured professional drivers test positive to amphetamines. The primary objective of the current thesis was to determine the underlying causes of these sleep- and drug-related accidents. Experimentally, driving performance can be broken down into specific components that can be examined independently. Measures of behavioural disposition provide an indication of the drivers’ mood, ability to determine a change in performance and sleepiness, and whether the driver can make appropriate decisions regarding their ability to drive safely when sleep-deprived. Simulated driving tasks are commonly used to detect driving-related performance in a controlled and safe environment. The task of driving involves a number of components, including attention and vigilance, processing speed and reaction time, visual processes, and executive functioning, which can be measured using neurocognitive tasks. Smaller, pre-conscious neural processes that are undetected by behavioural tasks may also be affected by sleep deprivation, and in turn, affect driving performance. Electrophysiological (eventrelated potentials; ERPs) and neuroimaging (functional magnetic resonance imaging; fMRI) measures can be used to determine the neural underpinnings of visual and auditory processes after sleep deprivation. The aim of this thesis was to determine the effects of one night of sleep deprivation on these driving-related processes in professional drivers. In Experiment 1, nineteen professional drivers underwent two randomised sessions; one session following a normal night of sleep and one session following 24-hours of sleep deprivation. Behavioural disposition, simulated driving performance, neurocognitive measures related to driving, and visual and auditory ERPs were examined in both sessions. Subjective ratings of sleepiness and sleepiness symptoms increased significantly following sleep deprivation. Simulated driving performance and neurocognitive measures of vigilance and reaction time were impaired after sleep deprivation, whereas tasks examining processing speed and executive functioning were less susceptible to sleep deprivation. Event-related potentials of visual and auditory processing indicated that early visual processes were unaffected by sleep deprivation, whereas the amplitude of later cognitive processing was attenuated after sleep deprivation. Driving also involves the ability of the driver to divide his or her attention between different sensory modalities in the driving environment. Experiment 2 presents a functional neuroimaging experiment examining the effect of sleep deprivation on neural activations that occur in response to a cross-modal divided attention task. There was no significant effect of sleep deprivation on behavioural performance. Following sleep deprivation, increased activation was observed in the temporal gyrus, cerebellum and precuneus, compared to activations observed after normal sleep. As no behavioural changes were observed, the results suggest that additional activation may act as a compensatory mechanism. The restorative effect of d-amphetamine on sleep deprivation related impairment was examined in Experiment 3. This pilot study examined eight professional drivers who were past or current users of amphetamine across four, randomised sessions; after normal sleep with oral placebo, after sleep deprivation with oral placebo, after normal sleep with 0.42mg/kg oral d-amphetamine, and after sleep deprivation and 0.42mg/kg oral d-amphetamine. Measures of behavioural disposition appeared to be more affected by d-amphetamine administration after sleep deprivation compared to simulated driving and neurocognitive performance, however these findings need further clarification in a larger sample. The results of the present thesis highlight the detrimental influence of sleep deprivation on a range of driving-related processes. The experienced, professional drivers in this study were able to recognise signs and symptoms of sleepiness, and acted upon these indicators appropriately. Measures of driving-related performance on both simulated driving, and simple neurocognitive tasks were negatively affected by sleep loss, although there is likely to be a discrepancy between on-road and laboratory behaviour. ERP and neuroimaging findings in the present thesis suggest that these sleep-related behavioural effects are caused by small changes in neural processing and neural recruitment. Sleep deprivation can have large implications for safe driving, and this study highlights the importance of promoting and educating the driving public about the dangers of driving when sleepy.
| Identifer | oai:union.ndltd.org:ADTP/244882 |
| Date | January 2009 |
| Creators | Jackson, Melinda L. |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright © 2009 Melinda Lee Jackson. |
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