Altered hemispheric functioning under alcohol.

Abstract

A visual search task which required subjects to locate the duplicates to complex nonsense figures or verbal stimuli (consonant-vowel-consonant trigrams) displayed in a visual array was completed by 40 students (men, mean age 24) under "delay" or "no-delay" conditions. Under the no-delay condition the target remained in the visual field during the search for the matching pattern; under the delay condition the target was removed from sight 10 s before the array was presented to the subject. Ten subjects were assigned to each of 4 groups: no-delay-alcohol or placebo, and delay-alcohol or placebo. All subjects were right-handed and light to moderate drinkers. None had a history of possible brain injury. The subjects in the alcohol groups received 1.04 g of 95% alcohol/kg of body weight in a 20% solution. The visual search task was performed when blood alcohol concentration (BAC) had reached 0.075-0.080% on the ascending BAC limb. The over-all mean response time was significantly longer in the alcohol than in the placebo groups (6.27 vs. 5.42 s, P < .05). It took longer to match shapes than verbal stimuli. No significant differences between delay and no-delay conditions were found. A significant interaction between alcohol, nature of the stimulus and visual area was demonstrated. Compared with the placebo groups, the alcohol groups had a significantly longer search time for shapes presented to the left visual area (P < .01), but the groups did not differ in search time for stimuli in the right visual area. Single doses of alcohol affect the neuropsychological functions subserved by the right hemisphere to a greater extent than functions controlled by the left hemisphere. Further analysis suggests that alcohol affects normal laterality functions and thus may also alter left hemisphere functions under certain conditions.