Summary: Researchers report that moderate alcohol intake diminishes brain waves linked to decision-making (theta oscillations) while leaving motor-related brain activity (beta oscillations) relatively intact.
Source: San Diego State University.
Alcohol is well known to impair judgment, alertness, and attention-dependent performance, yet the precise neural mechanisms behind these effects remain under study. A new experiment led by psychologists at San Diego State University clarifies how alcohol weakens cognitive control during decision-making while sparing basic motor preparation. The findings help explain why people who have been drinking often feel in control even though their capacity to make correct, timely choices is reduced—a dangerous combination when tasks like driving require rapid, flexible decisions.
In a study published in the journal PLOS ONE, Ksenija Marinkovic, director of SDSU’s Spatio-Temporal Brain Imaging Laboratory, and colleagues recruited 18 healthy young adults to perform a visual decision task while their brain activity was recorded with magnetoencephalography (MEG). During the experiment participants watched sequences of colored squares on a screen: first two peripheral squares (flankers) of the same color appeared, followed by a single central target square. On some trials the center square matched the flankers; on others it differed. Participants were instructed to ignore the flankers and press the button corresponding to the color of the central target.
Although the flankers were irrelevant to the instructed response, they automatically triggered premature motor preparation, explained study co-author Lauren Beaton, a graduate student in psychology at SDSU. “They unconsciously begin preparing to respond, as the flankers prematurely elicit automatic motor response before the actual target appears,” she said. Successfully overriding that automatic response requires cognitive control—the ability to monitor incoming information and adjust behavior flexibly when conflict or ambiguity arises.
Each participant completed the task in three conditions: sober, after consuming a moderate alcoholic beverage, and during a placebo session. While participants responded, the researchers measured two types of brain oscillations: theta (4–7 Hz) and beta (15–25 Hz). Theta oscillations are linked to communication between brain regions involved in decision-making and conflict monitoring, whereas beta oscillations are associated with motor preparation and the initiation of movement. In the task, theta reflected the process of choosing the correct button, while beta reflected preparing to send the motor command.
The key finding was a dissociation between these oscillatory systems under alcohol. Beta activity in sensorimotor regions—tracking motor preparation and the lateralized switch from an incorrectly primed hand to the correct hand—remained largely normal after drinking. In contrast, theta power, especially in medial and ventrolateral frontal areas tied to cognitive control, dropped sharply under alcohol.
“At its peak, theta power under alcohol decreased to roughly half of placebo levels,” Beaton said.
Behaviorally, alcohol selectively impaired accuracy when the flankers conflicted with the target: error rates rose by about five percent on incongruent trials. Reaction times, however, showed little change. Together these results indicate that moderate alcohol primarily disrupts the decision-making and conflict-resolution processes that determine correct responses, rather than the execution of motor commands once a choice is made.
In practical terms this pattern helps explain why intoxicated individuals may feel they are acting appropriately even as their ability to choose correctly is compromised. Routine behaviors—such as the largely automatic actions involved in driving—can be executed with little conscious oversight, but unexpected events require rapid cognitive control to override automatic responses. If alcohol blunts the frontal theta processes that support conflict monitoring and response switching, drivers who believe they can handle the road may in fact be less capable of making the quick, correct adjustments that prevent crashes.
“When driving, we usually operate on auto-pilot, going through the motions automatically and without much conscious thought,” Beaton added. “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 cognitive control to safely navigate the situation. But when drivers are intoxicated, they are less successful at making these quick changes.”
Source: San Diego State University
Publisher: Organized by NeuroscienceNews.com
Image credit: NeuroscienceNews.com (public domain)
Original research: Open-access study in PLOS ONE
DOI: 10.1371/journal.pone.0191200
When the brain changes its mind: Oscillatory dynamics of conflict processing and response switching in a flanker task during alcohol challenge
Daily behavior relies on the interaction between automatic sensory-evaluation and response-preparation streams and top-down cognitive control that intervenes when stimuli produce ambiguity or conflict. This study used anatomically constrained MEG to examine neural dynamics in a flanker task that manipulated stimulus-response incongruity at both stimulus and response levels. Although flankers were irrelevant, they triggered automatic motor plans that sometimes had to be suppressed and reversed after the target appeared. Beta-band (15–25 Hz) source power in sensorimotor cortex tracked motor preparation and revealed switching from an incorrectly primed hemisphere to the correctly responding one. In contrast, theta oscillations (4–7 Hz) were sensitive to incongruity levels: medial and ventrolateral frontal cortices were particularly activated by response conflict and contributed to response inhibition and switching through phase-locked co-oscillations. A moderate alcohol beverage selectively reduced accuracy during response conflict and strongly attenuated theta oscillations during decision-making, while leaving the beta-band motor switching processes largely intact. These findings indicate that motor preparation can be initiated automatically even when counterproductive, but that prefrontal cognitive control monitors and regulates these processes—functions that are especially vulnerable to alcohol intoxication.
This article summarizes experimental findings on how moderate alcohol affects neural oscillations involved in decision-making and motor preparation. The study relied on MEG recordings and a controlled flanker-task paradigm to distinguish cognitive control (theta) from motor preparatory activity (beta).