A study has found that people who are used to drinking a lot of alcohol regularly, are able to carry out some fine motor tasks, but more complex tasks may prove difficult. The participants in the study were not necessarily able to tell that they would be unable to carry out the task, misjudging how the drink had affected them. The study was led by a researcher from the Veterans Affairs San Diego Healthcare System.
The study aimed to examine whether experience of drinking to intoxication could lead to less impaired cognitive and psychomotor performance, as was commonly thought. The study also wished to examine whether behavioural tolerance develops or changes over time in adults who regularly drink heavily. The researchers examined data from 6 years of the Chicago Social Drinking Project to check the results.
The participants were divided into heavy drinkers, who consumed between 10 and 40 alcoholic drinks a week for at least the past two years and light drinkers, who had less than 6 drinks a week. Participants maintained their drinking habits during the project. They were given two tasks: the Grooved Pegboard, which is considered similar to unlocking a door with keys and Digit Symbol Substitution Test which is similar to a more complex task such as remembering directions to a new location or driving a car. Before the tasks, the participants were given a dose of alcohol that was calculated to bring them to a specific breath alcohol concentration according their body weight. They were tested at 30, 60, 120 and 180 minutes following the administration of drink. The tasks were then repeated 5 years later.
Previously light and heavy drinkers had shown similar levels of impairment on the tasks during the initial tests. During the five year follow-up, both sets of drinkers improved their abilities on the tasks which were attributed to practice effects by the study authors. Evidence of chemical tolerance to alcohol was shown by heavy drinkers whose breath-alcohol concentrations decreased more quickly at the follow-up test. This suggested that heavy drinkers are able to absorb and metabolise alcoholic drink more quickly than light drinkers. The group of heavy drinkers were able to carry out the pegboard task more easily than the light drinkers, but the two groups showed a similar amount of impairment when it came to the more complicated task.
The scientists suggested that the results of the study showed that people who are regularly heavy drinkers may be able to carry out simple fine motor skills tasks more easily than those who are light drinkers, however they will not be able to carry out more complex tasks which involve short-term memory and more complex motor processing. The researchers suggested that the behavioural tolerance developed may be due to changes at cellular level in the brain, enabling it to adapt and become less sensitive to alcohol. They also suggested that the participants learned to do the tasks while under the influence of alcohol during the study.
The scientists were also concerned that the heavy drinkers group reported lower self-perceived impairment than the light drinkers. They suggested that heavy drinkers could potentially engage in more risky behaviours while drinking because they might not understand how impaired they were. For example, a regular heavy drinker may be able to walk to their car and unlock the door with a key relatively easily but the task of driving the car would definitely be affected. Because the person had been able to carry out the tasks leading up to driving the car, they would most likely drive home, impaired. The researchers suggested that making such decisions would be highly risky because the decision would be made on faulty information.
Brumback, T., et al., Alcohol-induced performance impairment: a 5-year re-examination study in heavy and light drinkers, Psychopharmacology (2017). doi:10.1007/s00213-017-4577-x