Microsleep Episodes, Attention Lapses and Circadian Variation in Psychomotor Performance in a Driving Simulation Paradigm

Numerous studies document circadian changes in sleepiness, with biphasic peaks in the early morning and late afternoon. Driving performance has also been demonstrated to be subject to time-of-day variation. This study investigated circadian variation in driving performance, attention lapses (AL) and/or frequency of microsleep (MS) episodes across the day. Sixteen healthy adults with valid driver’s licenses participated in the study. Using the York Driving Simulator, subjects performed four intentionally soporific 30-minute driving simulations at two-hour intervals (i.e., at 10:00, 12:00, 14:00, and 16:00). During each session, individuals had EEG monitoring for MS episodes (defined as 15 to 30 seconds of any sleep stage by polysomnographic criteria) and AL episodes (defined as intrusion of alpha- or theta-EEG activity lasting 4-14 seconds). Measured variables included: lane accuracy, average speed, speed deviation, mean reaction time (RT) to “virtual” wind gusts and off-road events. Mean values of each variable at every time were analyzed using a general linear model and paired sample t-tests. RT displayed significant within-group variation, with paired samples tests at df=15 showing RT at 10:00 significantly faster than at other times of the day, but no significant within-group variation between other times of the day. All other variables and EEG-defined AL episodes failed to exhibit any statistically significant variation across the day. However, MS episodes were found to occur more often at 16:00 in comparison to all other times. As RT was optimal before noon, it appears that psychomotor performance and therefore driving ability is subject to circadian variation. Coincident with the demonstrated circadian pattern of diminished alertness, this may partially explain the high incidence of motor vehicle accidents during the mid- to late-afternoon. By better understanding circadian fluctuations in driver sleepiness and psychomotor performance, human performance researchers may be in a position to better educate the public about cautionary measures to prevent accidents

Simulator Performance vs. Neurophysiologic Monitoring: Which is More Relevant to Assess Driving Impairment?

Previously, we reported on circadian variation in driving simulator performance and neurophysiologic evidence of sleep intrusion into consciousness in a pilot study of healthy individuals. We have since expanded this “normative” sample and run a prospective comparison study with a sample of clinical patients reporting excessive daytime sleepiness (EDS) as a chief complaint. Thirty healthy adults (mean age of 31.3 ± 11.5) and 27 EDS patients (47.0 ± 13.7) with valid driver’s licenses were included. Subjects performed four intentionally soporific 30-minute driving simulations at two-hour intervals while undergoing continuous EEG monitoring for microsleep (MS) episodes. Measured variables included: subjective ratings of sleepiness and alertness prior to each drive, lane position accuracy, mean speed, speed deviation, mean reaction time (RT) to “virtual” wind gusts as well as off-road events, i.e., “crashes.” In comparing normative individuals and EDS patients, significant between-group differences were found between subjective ratings, RT, crashes and MS. Both groups showed a significant a tendency towards RT slowing during afternoon drives, with this circadian effect appearing most pronounced for EDS patients. Significant between-group differences were also found on subjective ratings of sleepiness and alertness, although diurnal fluctuation of subjective sleepiness ratings was significant only for the EDS group. Objective EEG MS monitoring demonstrated escalating sleep intrusion with repeated drives in both groups, but particularly for the EDS group. Total crash rates were three times higher in EDS patients, with an increasing trend towards crash-proneness in the late afternoon. In summary, we found significantly impaired performance on some, though not all, driving parameters for EDS patients. While increased crash rate may be the most dramatic of these, slowing of RT was the most statistically robust. EEG monitoring was able to document increased propensity towards MS episodes in patients with EDS, which we suggest is causative in creating this impairment. It remains unclear whether a neurophysiologic or simulator approach captures impairment due to sleepiness with greater sensitivity and specificity. A hybrid approach combining data from both sources may be optimal, and also could be integrated in commercial vehicle use. We suggest that the need for a more accurate hospitalbased screening tool for assessment of driving impairment due to sleep disorders remains an important issue for physicians and legislators dealing with driving competency

Sleep disorders, sleepiness and traffic safety: a public health menace

Sleep disorders are not uncommon and have been widely reported throughout the world. They have a profound impact on industrialized 24-h societies. Consequences of these problems include impaired social and recreational activities, increased human errors, loss of productivity, and elevated risk of accidents. Conditions such as acute and chronic insomnia, sleep loss, excessive sleepiness, shift-work, jet lag, narcolepsy, and sleep apnea warrant public health attention, since residual sleepiness during the day may affect performance of daily activities such as driving a car. Benzodiazepine hypnotics and zopiclone promote sleep, both having residual effects the following day including sleepiness and reduced alertness. In contrast, the non-benzodiazepine hypnotics zolpidem and zaleplon have no significant next-day residual effects when taken as recommended. Research on the effects of wakefulness-promoting drugs on driving ability is limited. Countermeasures for excessive daytime sleepiness have a limited effect. There is a need for a social awareness program to educate the public about the potential consequences of various sleep disorders such as narcolepsy, sleep apnea, shift-work-related sleep loss, and excessive daytime sleepiness in order to reduce the number of sleep-related traffic accidents.Mount Sinai School of Medicine Division of Pulmonary, Critical Care, and Sleep MedicineUniversity of Utrecht Utrecht Institute for Pharmaceutical Sciences Department of PsychopharmacologyUniversity of Toronto, and Sleep and Neuropsychiatry Institute Department of PsychiatryUniversidade Federal de São Paulo (UNIFESP) Departamento de PsicobiologiaUNIFESP, Depto. de PsicobiologiaSciEL

Farit Gabidinovich Avkhadiev (on his 70th birthday)

This article about mathematical results of F.G. Avkhadiev

Farit Gabidinovich Avkhadiev (on his 70th birthday)

This article about mathematical results of F.G. Avkhadiev