Public Release: 

The cognitive damage of alcohol lingers after motor performance returns to normal

Alcoholism: Clinical & Experimental Research

  • The human ability to process information is divided into three stages: stimulus identification/ perception, response selection/cognition, and response execution/motor processes.
  • A new study examines alcohol's effects on response selection/cognition.
  • Alcohol-related impairment of cognitive functioning appears to linger after motor performance returns to normal.

The human ability to process information is divided into three stages: stimulus identification/perception, response selection/cognition, and response execution/motor processes. Tasks such as driving a car involve a complicated interaction of all three information-processing components. Researchers know from previous studies that alcohol slows information processing, but the specifics remain unclear. A study in the April issue of Alcoholism: Clinical & Experimental Research has found that alcohol impairs cognitive functioning even when motor functioning appears normal.

"Given that most tasks require some information processing and that alcohol is one of the most commonly used recreational drugs, we felt that a more thorough examination of how alcohol disrupts the stream of information processing was warranted," said Tom A. Schweizer, currently a postdoctoral fellow at the Rotman Research Institute in Toronto and first author of the study. "What is not clear from earlier studies is whether this disruption is attributable to a specific slowing of one stage - that is, perceptual, cognitive or motor - or a slowing of all stages within the information-processing stream. Also, few studies have looked specifically at the differential effects of alcohol on cognitive functioning during rising and declining blood alcohol concentrations (BACs). One of the goals of this research was to address whether or not cognitive functioning behaves like motor functioning during rising and declining BACs."

Schweizer and his colleagues examined 34 healthy, male social drinkers using the psychological refractory period (PRP) paradigm.

"The PRP paradigm tests the limits of a person's ability to process information when two tasks are completed in rapid succession," said Schweizer. "PRP refers to the delay in processing the information from a second task stimulus when it closely follows the first task stimulus. Specifically, if alcohol disrupts the cognitive stage of information processing, a greater delay in responding - meaning an increase in reaction time - to the second task should be observed."

Participants were randomly assigned to one of two groups (each n=17); one group received a placebo while the other received a moderately high dose of alcohol (peak blood alcohol of 0.10%). A trial on the dual task consisted of a Task 1 stimulus (a frequency tone of 200, 500, 1250 or 3125 Hz) followed by a Task 2 stimulus (either the letter H, O or S), separated by one of four delays (either 50, 200, 500 or 1100 milliseconds). Reaction times and errors were recorded for both groups at baseline (prior to drug administration), and while BACs were rising and declining.

Compared to their baseline measures, the alcohol group made significantly more errors during the ascending phase of the BAC curve; moreover, this increase in errors continued during the descending phase of the BAC curve. The alcohol group also demonstrated longer reaction times during rising BACs, however, response times returned to baseline levels when BACs were declining.

"Our findings indicate that the motor component of information processing recovers during declining BACs, but it appears that the cognitive effects of the drug linger well after motor performance is back to drug-free levels," said Schweizer. "The reduction in motor impairment as BACs decrease could create the illusion of complete sobriety and prompt the undertaking of activities requiring cognitive processes that are still greatly impaired. However, the reaction time may have recovered, but the cognitive system is still under the influence of the drug and could result in the individual making a serious error."

Schweizer used the example of driving. "One could envision a scenario in which the brake lights on the car ahead suddenly come on," he said. "To avoid a collision, a driver must swiftly remove his or her foot from the gas and depress the brake. A driver whose BACs are decreasing may react as swiftly as normal but may respond incorrectly by slamming on the accelerator rather than the brake. The speed of response is the same, but the driver has just made a costly error."

Schweizer said this research highlights the importance of measuring both speed and accuracy of cognitive performance when investigating the effects of alcohol intoxication. "The results also highlight the importance of testing the effects of alcohol at various points on the blood alcohol curve," he said. "Depending on where you test on the BAC curve you could get vastly different results. This is especially true for tasks that tap into cognitive functioning."

Schweizer suggested that readers take extra caution when attempting to gauge their own recovery from the effects of acute alcohol intoxication. "The mismatch between motor and cognitive recovery ... creates special hazards that may have implications for accident risks. A drinker who is about to drive a vehicle immediately after recovering from a drinking episode may be more dangerous than while actively drinking because they mistakenly assume they're okay."


Alcoholism: Clinical & Experimental Research (ACER) is the official journal of the Research Society on Alcoholism and the International Society for Biomedical Research on Alcoholism. Co-authors of the ACER paper, "Fast, but error prone responses, during acute alcohol intoxication: Effects of stimulus-response mapping complexity," were: Pierre Jolicœur of the Département de Psychologie at the Université de Montréal; and Muriel Vogel-Sprott and Mike J. Dixon of the Department of Psychology at the University of Waterloo. The study was funded by the Natural Sciences and Engineering Research Council of Canada.

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