Why the Buzzed Brain Thinks It Knows What Its Doing
A new study by 色情视频 psychologists found that alcohol dampens brain waves associated with decision-making but not motor control.
In a in the journal PLOS ONE, a team led by psychologist Ksenija Marinkovic, director of 色情视频鈥檚 Spatio-Temporal Brain Imaging Laboratory, recruited 18 young, healthy volunteers to participate in an experiment measuring their cognitive control while distracted. The volunteers sat in a brain imaging machine called a MEG scanner and watched 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鈥檚 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鈥檚 not easy to disregard the irrelevant side squares, which are known as flankers, explained study co-author Lauren Beaton, a graduate psychology student at 色情视频.
鈥淭hey unconsciously begin preparing to respond, as the flankers prematurely elicit automatic motor response before the actual target appears,鈥� she said. 鈥淭o do this successfully requires recruitment of cognitive control. That means having the capacity to monitor attentional demands and respond to them flexibly.鈥�
It鈥檚 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鈥檚 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鈥檚 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鈥攂ut their theta waves dropped sharply in frequency.
鈥淎t its peak, theta power under alcohol decreased to roughly half of placebo levels,鈥� Beaton said.
After drinking, the volunteers鈥� accuracy at the color-choosing task also fell by about five percent whenever the flanker squares didn鈥檛 match the target square. Interestingly, reaction time stayed about the same. Taken together, the results suggest 鈥渢hat alcohol primarily induces deficits during decision-making, and not while executing motor commands,鈥� Beaton said.
In other words, the brain still thinks it鈥檚 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.
鈥淲hen driving, we usually operate on auto-pilot, going through the motions automatically and without much conscious thought,鈥� she said. 鈥淗owever, 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 cognitive control to safely navigate the situation. But when drivers are intoxicated, they are less successful at making these quick changes.鈥�
