By Merritt McKinney

NEW YORK, Mar 21 (Reuters Health) - Researchers studying the brains of people with a family history of alcohol abuse have identified key differences that may predispose people to compulsive drinking.

The problem seems to be an imbalance between two chemical signaling systems that regulate the stimulation and inhibition of brain cells, according to the scientists from the State University of New York Health Science Center at Brooklyn.

Since alcohol quickly acts on the brain pathway involved in stimulation or "excitability," the findings suggest that alcoholics may drink to restore the balance in their brains, according to one of the study's authors.

Just as the body depends on a regular heartbeat to live, the balance between the neurotransmitters that control inhibition and excitability is "absolutely critical" for proper brain function, Dr. Henri Begleiter told Reuters Health.

And, according to Begleiter, the evidence is also firm that a deficit in the inhibiting system in the brain may also lead to less inhibited behavior, which causes many alcoholics to take more risks and to be more aggressive and antisocial.

In the study, the investigators measured the electrical activity in the brains of two groups of non-alcoholic teens and young adults: 16 with a family history of alcoholism and 22 at low risk of becoming an alcoholic.

While the patients were reading, they listened through headphones to a series of tones. During the exercise, the tones were occasionally changed slightly. Through electrodes attached to the participants' heads, the researchers were able to measure the brain's electrical activity when the tones changed.

In the interview, Begleiter explained that the changes in tone produce a negative response in the brain's electrical activity. This response, called mismatched negativity, is a measure of brain excitability.

The study found that mismatched negativity tended to be larger in people at high risk for alcoholism than in low-risk individuals. The findings are published in the March issue of the journal Alcoholism: Clinical and Experimental Research.

The results shed more light on the imbalance present in the brains of people at high risk of becoming an alcoholic, according to Begleiter.

"We've never (before) been able to prove the excess of excitation," he added.

In the report, the authors note that alcoholics may drink to "self-medicate" the imbalance. Begleiter pointed out that alcohol can quickly restore the balance in the brain since it acts directly on a neurotransmitter involved in excitability.

"It does the trick very well," he said.

But as they build up a tolerance to the effects of alcohol, however, alcoholics may have to drink more and more to get the same effect.

Begleiter's team now plans to study a sample of teenagers from the general population to see whether it is possible to use mismatch negativity readings to predict who will later become an alcoholic. The long-term research goal, he said, is to understand the genes involved in the imbalance and possibly develop drugs to prevent it.

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