Acute dose of alcohol affects cognitive components of reaction time to an omitted stimulus: differences among sensory systems

Rational: The possibility that moderate blood alcohol concentrations (BACs) may impair cognitive processes before disturbing motor functions has raised concern about the safety of BACs <= 80 mg/100 ml. Reaction time (RT) to the presentation of a stimulus or to the omission of a regularly occurring stimulus has been fractionated into independent premotor (cognitive) and motor (movement) components. It has been suggested that cognitive processes may be impaired at lower BACs than are motor processes, but the effects of moderate rising and declining BACs on these component RT measures have not been investigated. Objectives: An omitted stimulus RT task was used to test the hypothesis that moderate rising BACs impair (slow) premotor RT (PMRT) when motor RT (MRT) remains unaffected. The task included visual, auditory, and tactile stimuli to explore differences in sensory sensitivity to alcohol. Methods: Thirty male social drinkers were randomly assigned to three groups (n=10) that received 0.62 g/kg alcohol, 0.8 g/kg alcohol, or a placebo (0 g/kg). All participants performed the task three times: baseline and during rising and declining BACs. Results: Comparisons of the alcohol and placebo groups showed rising BACs slowed PMRT and had no detectable effect on MRT. Impairment in visual PMRT occurred under both alcohol doses. Auditory PMRT was impaired only under the 0.8 g/kg dose, and tactile PMRT was unaffected. Conclusions: Cognitive functions are impaired by moderate increasing BACs that do not affect motor movement, and the tactile sensory system may be relatively insensitive to this impairment.