Causes & consequences of alcohol-related brain shrinkage

Previous studies have demonstrated that the brains of alcoholics are smaller, lighter and “shrunken” when compared to non-alcoholic brains.

“The outer layer of brain, also called the gray matter, controls most complex mental activities, “explained Clive Harper. “The cortex is filled with nerve cells, also called neurons, that connect by single long fibres to different brain regions and other neurons deep inside the brain and spinal cord. These nerve fibres make up white matter, which comprises the ‘hard wiring’ of the brain. Most of the fibres are insulated by a material called ‘myelin’ that is similar to the plastic coating around electrical wires. Nerve cells also have shorter and more numerous fibres or processes called dendrites with many fine branching processes – similar to the root system of a tree – that allow them to ‘talk’ with neighboring neurons, often as many as five to 10,000 at a time.”

The nerve cell or neuron

Alcohol appears to be particularly damaging to the “white matter” or “hard wiring” of the brain, and can also cause shrinkage or retraction of neuron dendrites; however, the damage appears to be at least partially reversible with abstinence.

A number of toxic, metabolic, and nutritional factors interact in a complex way to cause brain damage in those individuals who abuse or are dependent on alcohol.

“The exact ways in which alcohol damages the brain are uncertain,” said Harper. “It might be that alcohol, or a metabolic byproduct of alcohol are toxic.

Research on malnutrition, a common consequence of poor dietary habits in some alcoholics, indicates that thiamine deficiency can contribute to impaired thinking. Cirrhosis of the liver, also common in alcoholics, is known to cause clinical and structural changes in the brain. In addition, head injury and sleep apnoea are more common in alcoholics and can contribute to brain damage.

All of these factors – particularly the alcohol, thiamine deficiency and cirrhosis – are linked and probably contribute in a complex way to cause brain damage.”

Both permanent and transient changes may occur in the alcoholic brain.

“The most important permanent structural change is nerve cell loss,” said Harper. “Some nerve cells cannot be replaced, some of those in the frontal cortex, cerebellum and several regions deep in the brain.”

However, he added, some changes can be transient, such as the shrinkage of dendrites, those fibers that allow neurons to “talk” with neighboring neurons. “In experimental animals,” he said, “these have been shown to grow and spread again after periods of abstinence – weeks to months – and have been accompanied by improved brain function.

Changes seen in cirrhosis of the liver are also potentially reversible if treated. Furthermore, thiamine deficiency can be treated easily with oral or injected thiamine. Patients with acute deficiency respond very quickly but some permanent damage can occur if patients are not treated and particularly if they suffer repeated episodes of the deficiency.”

It is important for people who abuse alcohol to realize that some of the damage can be reversed.

“Brain / psychological studies have shown that some brain functions improve with abstinence,” said Harper. “Although working memory, postural stability, and visuospatial ability may continue to show impairment for weeks to months with sobriety, with prolonged sobriety these brain functions can show improvement.”

Some alcoholics can achieve long-term abstinence in spite of persistent deficits in decision-making.

“There is accumulating evidence that the inherited vulnerability to alcoholism and other addictions involves abnormal parts of the brain systems that process rewards and punishments,” said George Fein.

“People with an inherited vulnerability to addiction, including alcoholism, are much more affected by immediate than delayed rewards. A hallmark of addictive substances is that they provide an immediate reward in the intoxicating experience. When actively drinking, an individual’s inhibition processes become impaired and can further contribute to poor decisions and excessive drinking.

 side-view-of-brain.gif

The side view of the human brain

With prolonged bouts of drinking, dependence may result along with neural systems damage, commonly affecting frontal lobe based systems and their functions, which include decision making, inhibition, problem solving, and judgment. This is part of the dynamic course of alcoholism that likely contributes to its maintenance. We presented data showing that alcoholics can overcome these disabilities in decision making and rating of rewards and punishments to achieve multi-year sobriety.”

People who abuse alcohol,” he added, “should be informed that some of the brain damage could be reversed.”

Research was published in the June issue of Alcoholism: Clinical & Experimental Research.

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