Alcohol Impairs More Than Motor Skills

Drinking alcohol can impair both motor skills and cognitive functioning, but as you sober up you regain motor skills at a faster rate that you do cognitive function, which could give you a false sense of security.

As you begin to recover from a bout of heavy drinking, and your blood-alcohol content begins to decrease, you regain some of your motor skills—such as those needed to operate a vehicle - faster than you regain the ability to identify and respond to information.

Therefore, you may be able to make a physical reaction—for example, to another vehicle suddenly stopping in front of you—as quickly as you could while not drinking, but you may make the incorrect response—such as pressing the accelerator rather than the break.

Processing Information

There are three stages to processing information:

• Stimulus identification/perception
• Response selection/cognition
• Response execution/motor processes

When you are impaired by alcohol your ability to process information slows down.

Slowing of Information Processing

"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, of 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)," he said. "One of the goals of this research was to address whether or not cognitive functioning behaves like motor functioning during rising and declining BACs."

Delays in Responding

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."

Schweizer's study examined two groups of 17 participants, one of which was given enough alcohol to peak their blood-alcohol content at 0.10. Their reaction times were recorded at baseline and while their BACs were rising and declining.

Significantly More Mistakes

The experiment's findings included:

• The alcohol group made significantly more errors during the ascending phase of the BAC curve
• Errors continued during the descending phase of the BAC curve
• The alcohol group demonstrated longer reaction times during rising BACs
• Response times returned to baseline levels when BACs were declining

Cognitive Skills Recover More Slowly

"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."

"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."

Speed and Accuracy Should Be Tested

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."

Increased Risks for Accidents

The researchers suggested that drinkers 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."