Electroencephalogram tests for brain dysfunction: a question of validity.

centrations of diazepam in the blood, but previous studies (7) have shown that a single 10-mg oral dose will, after I to 2 hours, produce concentrations similar to those in patients following a typical dosage regimen of 5 mg, three times daily. This does not imply that shortand longterm diazepam effects will necessarily be the same because of equivalent blood concentrations, nor that healthy volunteers will react like patients in any case. We cannot conclude from our results that diazepam will render all drivers, and particularly habitual diazepam users, unable to operate a motor vehicle safely. Patients possessing less driving skill than our subjects, however, might be expected to react even more adversely when beginning diazepam therapy. If they eventually adapt to long-term treatment in ways reducing the diazepam effect upon driving performance, their impairment would pass. Until this can be demonstrated, however, it would be prudent to assume that many diazepam users are impaired to some degree. The measured impairment was confined to a loss of the subjects' ability to control the lateral position of the vehicle during high-speed travel on straight roads. It was apparent for most subjects in conditions D-10, but to widely different degrees. In two subjects, and possibly three, impairment reached levels that might rightfully be called dangerous. Their standard deviation of lateral position exceeded that associated with the containment of lateral movement within lane boundaries [about 35 cm (8)], and their movement extended into adjacent lane and shoulder areas. Because these excursions appeared involuntary, one might assume that their control ability had diminished below that required to operate safely on normal roads. Volitional effort, which allowed the subjects to comply with speed instructions, was apparently insufficient to overcome the effect of diazepam on lateral variability. The correlation between changes in lateral variability from control conditions to D-10 and M may provide some clue about the mechanism of the diazepam effect. Performance changes in both cases were accompanied by a corresponding drop in subjective arousal. Those individuals whose performance deteriorated with the normal loss of arousal that accompanies prolonged wakefulness showed even greater impairment accompanying loss of arousal after the 10-mg diazepam treatment. The lability of the arousal process might therefore be the individual mitigating factor that determines the drug's effect