Alcohol affects decision-making but not motor control : Study

Lauren E. Beaton and colleagues at San Diego State University conducted a study to find out the mechanism behind the effect of alcohol on cognition.The researchers have found out that Alcohol affects decision-making but not motor control.That is why people feel like they are in complete control of their actions when they're drinking even while their cognitive control is clearly impaired.The study has been published in the journal PLOS ONE.

Alcohol selectively decreased accuracy to response conflict. It strongly attenuated theta oscillations during decision making and partly re-sculpted relative contributions of the frontal network without affecting the motor switching process subserved by beta band. Our results indicate that motor preparation is initiated automatically even when counterproductive but that it is monitored and regulated by the prefrontal cognitive control processes under conflict. The researchers further confirmed that the regulative top-down functions are particularly vulnerable to alcohol intoxication.

The team of researchers used anatomically-constrained MEG scanner to examine the underlying neural dynamics in a flanker task that manipulated S-R incongruity at the stimulus (SI) and response levels (RI) They recruited 18 young, healthy volunteers to participate in an experiment to measure their cognitive control while distracted. The volunteers were made to sit in a brain imaging machine called a MEG scanner and to watch a series of colored squares appear on a screen.

First, two squares of the same color would appear on either side, followed by a single square flashing in the middle of the screen. At times, the middle square’s color would match the two side squares and sometimes it would be different. Participants were instructed to ignore the color of the side squares and press a button corresponding to the color of the middle square.

Even though the participants understood what they were supposed to do, it’s not easy to disregard the irrelevant side squares, which are known as flankers, explained study co-author Lauren Beaton, a graduate psychology student at SDSU.

“They unconsciously begin preparing to respond, as the flankers prematurely elicit automatic motor response before the actual target appears,” she said. “To do this successfully requires recruitment of cognitive control. That means having the capacity to monitor attentional demands and respond to them flexibly.”

It’s a difficult enough task when sober, but the volunteers also took the task after consuming an alcoholic beverage, as well as during a placebo phase. During all three conditions (sober, placebo and alcohol) the scientists used the imaging machine to measure brain waves known as beta and theta oscillations, which are waveforms produced by the brain’s electrical activity.

Theta waves are involved in communication between different regions of the brain during decision-making, while beta waves are involved in motor control and preparing for movement. In the experiment, for example, theta waves reflect the brain deciding which button is the correct color to press, while beta waves reflect the brain’s preparing to send signals to the muscle.The researchers found that after participants drank alcohol, their beta waves during the color-choosing task seemed perfectly normal—but their theta waves dropped sharply in frequency.

“At its peak, theta power under alcohol decreased to roughly half of the placebo levels,” Beaton said.

In other words, the brain still thinks it’s making the right choices, even though its ability to do so is impaired.

That pernicious effect is especially troublesome for a task like driving, Beaton added.

After drinking, the volunteers' accuracy at the color-choosing task also fell by about five percent whenever the flanker squares didn't match the target square. Interestingly, reaction time stayed about the same. Taken together, the results suggest "that alcohol primarily induces deficits during decision-making, and not while executing motor commands," Beaton said.

“When driving, we usually operate on auto-pilot, going through the motions automatically and without much conscious thought,” she said. “However, occasionally we have to quickly react to stimuli, such as when a car cuts you off. You must be able to override automaticity and use the cognitive control to safely navigate the situation. But when drivers are intoxicated, they are less successful at making these quick changes.”

For more details click on the link: https://doi.org/10.1371/journal.pone.0191200