Impaired perceptual judgment at low blood alcohol concentrations

Abstract

Males and females show different patterns of cognitive impairment when blood alcohol concentrations (BACs) are high. To investigate whether gender differences persist at low BACs, cognitive impairment was tested in 21 participants (11 female, 10 male) using a brief computerized perceptual judgment task that provides error rate and response time data. Participants consumed a measured dose of alcohol (average peak BAC: females: 0.052 g/100 mL, males: 0.055 g/100 mL), and were tested at four time points spanning both the rising and falling limbs of the BAC curve, in addition to a prealcohol time point. Comparisons were made against performance of these same participants at equivalent time points in an alcohol-free control condition. Males and females displayed a trend toward slower responses and more errors, even when mildly intoxicated. These data indicate that cognitive function can be impaired at BACs that are below the legal limit for driving in most countries.

Introduction

Alcohol intoxication plays a role in one-third of injury-related deaths in females and almost half of them in males (Sjogren et al., 2006). Gender differences in cognitive impairment resulting from alcohol intoxication have been suggested to contribute to the different nature and frequency of accidents sustained (Ogden and Moskowitz, 2004). Females for instance, metabolize alcohol more quickly (Baraona et al., 2001, Frezza et al., 1990), show greater impairments in psychomotor performance (Dougherty et al., 1998, Fillmore and Vogel-Sprott, 1994) and have higher subjective ratings of their individual level of intoxication (Lundahl et al., 1997, Read et al., 2004). Intoxicated females have been found to display greater impairment on a short-term verbal memory task (Jones and Jones, 1976), a delayed recall task (Jones and Jones, 1977), and in the speed taken to access information from episodic memory (Haut et al., 1989). By contrast, intoxicated males have greater deficits in mental arithmetic and retrieving items from short-term memory (Hindmarch et al., 1991). In addition, intoxicated males display a greater reduction in cerebral glucose metabolism (Wang et al., 2003).

Most gender-based comparisons of alcohol-induced impairment have used a blood alcohol concentration (BAC) of 0.08–0.12 g/100 mL, presumably because the legal limit for driving in the United Kingdom and in most of North America is 0.08 g/100 mL. It is not known whether gender differences persist at lower BACs, such as 0.05 g/100 mL, which is the legal maximum limit for driving in Austria, France, Germany, Italy, and Australia. The present study aims to determine whether gender-based differences in alcohol-induced cognitive impairment can be detected at relatively low BACs. The paradigm involves a single time of alcohol administration and multiple-test sessions, using a short cognitive test. The use of a brief measure of cognition has enabled cognitive performance to be closely matched to BAC on both the ascending and descending limbs of the BAC curve.

The subtle cognitive impairment test (SCIT) (Yelland et al., 2004) is a computer-based, nonverbal, visuospatial discrimination task that assesses the speed and accuracy of perceptual judgments on briefly presented stimuli. It is believed that the requirements of the task mirror rapid perceptual judgments that might be made while driving. Although it shares some features with the inspection time (IT) task (Vickers et al., 1972) such as not being prone to practice effects, the SCIT has a quicker administration time (approximately 5 min duration compared with 25 min, and it provides measures of both error rate and response time; Friedman et al., 2006, Hutchison et al., 2006). The SCIT has not been used before to measure the effects of alcohol intoxication; however, the IT task has detected impairment in subjects with a BAC as low as 0.05 g/100 mL (Tzambazis and Stough, 2000). In the present study, the SCIT was used to compare the performance of males and females as they approach a target BAC of 0.05 g/100 mL and then recover.