Researchers know that many alcoholics continue to experience cognitive deficits even after long-term abstinence from alcohol. Results from a study in the April issue of Alcoholism: Clinical & Experimental Research confirm that motor deficits also continue to plague abstinent alcoholics. Furthermore, by using functional magnetic resonance imaging (fMRI) to "watch" brain regions involved in a simple motor task – finger tapping – the study has found that the brain appears to compensate for alcohol-induced damage by "recruiting" other, unexpected brain regions.
"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 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."
While undergoing MRI, two groups of participants performed repetitive, self-paced index finger-tapping exercises: eight (7 male, 1 female) alcohol-dependent patients after approximately two weeks of abstinence; and nine (7 females, 2 males) healthy volunteers or "controls." Participants alternated between using their dominant hands (DH) and non-dominant hands (NDH) to perform the index finger-tapping exercises. Researchers used fMRI analysis to compare DH and NDH performance in each subject group in order to examine whether the groups differed in the patterns of activation they exhibited in the cerebral cortex and cerebellum.
The detoxified alcohol-dependent patients performed the finger-tapping tasks significantly slower than the control group. However, 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 DH tapping. In other words, the alcoholics had to use more of their brains to do less.
"First, we found that alcoholics, 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."
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 same side, ‘contra’ means opposite side. So, we’re talking about my contralateral cortex and my ipsilateral cerebellum. The significantly higher activity we found in the alcoholics was on 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 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."
Martin added that these findings would not have been possible without the advantages of technological advances. "We as doctors can look at our patients and say ‘this patient is performing at a normal rate,’" he said, "but it’s not until we’re able to study the concomitant brain activation that is required to perform a task that we can understand that there actually are abnormalities."
These findings lead to new questions, said Martin. "If we study patients as they progress with their abstinence, 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."
Funding for this Addiction Science Made Easy project is provided by the Addiction Technology Transfer Center National Office, under the cooperative agreement from the Center for Substance Abuse Treatment of SAMHSA.
Articles were written based on the following published research:
Parks, M.H., Morgan, V.L., Pickens, D.R., Price, R.R., Dietrich, M.S., Nickel, M.K., Martin, P.R. (April 2003). Brain fMRI activation associated with self-paced finger tapping in chronic alcohol-dependent patients. Alcoholism: Clinical & Experimental Research, 27(4), 704-712.
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