How the Brain Compensates for Alcohol Abuse Damage

Although much of the damage thatchronic alcohol abusedoes to the brain begins to reverse after the alcoholic stops drinking, some cognitive deficits continue even after long-term abstinence.

One study has found that even some motor-skill deficits caused by long-termalcohol abusealso remain long after the alcoholic is abstinent. But, the unexpected news is there is evidence that the brain tries to compensate for that damage by using other regions of the brain to perform those tasks.

Using functional magnetic resonance imaging (fMRI), scientists were able to observe regions of the brain during a simple motor task and found that the brain appears to "recruit" other, unexpected regions to compensate for酗酒带来的危害.

Brain Regions Damage in Alcoholics

"We know from neuropathological studies that the two parts of the brain that are most often damaged in chronic alcoholics are the cerebellum and the frontal lobes," said Peter R. Martin, professor of psychiatry and pharmacology, director of the Vanderbilt Addiction Center at the Vanderbilt University School of Medicine, and corresponding author for the study. "Rapid self-paced motor activity such as finger tapping is a function of the motor cortex, the posterior part of the frontal lobe, which initiates a stimulus to the muscles of the hand, that is then coordinated by the interplay between the cerebellum and the frontal lobes.

"In other words, I reasoned that there would probably be abnormalities in activation of these regions in alcoholics during finger tapping."

Examining Brain Activity

Martin and colleagues observed two groups undergoing fMRI while performing repetitive, self-paced index finger-tapping exercises, alternating between their dominant and nondominant hands.

The groups were eight (7 male, 1 female) alcohol-dependent patients after approximately two weeks of abstinence; and nine (7 females, 2 males) healthy volunteers or controls.

Using More of the Brain

As expected, the abstinentalcohol-dependentpatients performed the finger-tapping tasks significantly slower than the controls.

Contrary to expectations, the slower tapping was not accompanied by proportionately decreased fMRI brain activation in the cerebral cortex and cerebellum; rather, the alcoholics had a significant increase of activation in the cortical brain region ipsilateral to (on the same side as) the active hand during the dominate hand tapping.

"First, we found thatalcoholics, generally speaking, tapped more inefficiently," said Martin. "Second, in order to generate a single tap, an alcoholic would activate a larger part of their brain than a normal person. So, the results seem to indicate that even though alcoholics, as they recover from drinking, can probably demonstrate relatively normal tapping, they have to use more of their brain to generate the taps."

"This study underlines the importance of considering the operation of brain circuitry involved even in an ostensibly simple task," said Edith Sullivan, associate professor of psychiatry at Stanford University School of Medicine. "Further, evidence for recruitment of brain regions that are not normally involved in a given task puts a person at risk for performance inefficiency for that particular task, other tasks that need to be done simultaneously, and more complex divided-attention tasks, such as driving."

Higher Brain Activity

Increased activity in the ipsilateral cortical region of the brain was highly unexpected, said Martin.

"Normally, when I tap with my right hand," he said, "it's mostly my left motor cortex (part of the frontal lobes) that's firing, in conjunction with my right cerebellum. 'Ipsi' means the same side, 'contra' means the opposite side. So, we're talking about my contralateral cortex and my ipsilateral cerebellum. The significantly higher activity we found in the alcoholics was in the ipsilateral cortex, the side that we don't normally expect to be activated.

"This finding is compatible with the idea that different regions of the brain are being called into an activity that would not normally be activated in order to meet the behavioral demands. Furthermore, this suggests that even though alcoholics at some level may seem to be performing normally if you raised the level of complexity at which they are being asked to perform, they may exhaust their capacities—there may be no more brain to bring in, to recruit, to compensate."

The Brain Gets Better at Compensating

These findings lead to new questions, said Martin. "If we study patients as they progress with theirabstinence, do these abnormalities get better? It may be that the brain gets better at compensating, but it doesn't normalize, it just learns how to bring in, even more, parts of the brain. You could say it learns to rewire itself.

"Another possibility could be that as the brain heals, less activation is required, and that's a real form of recovery. The answers rest with understanding not the tapping itself, but the mechanisms behind the tapping."