Healing Minds

STUDIES SHOW ADDICTION CHANGES THE BRAIN

Most people know that the use of some street drugs damages the brain.
A popular commercial several years ago showed a whole egg as your
brain and a frying egg as your brain on drugs. The idea that drugs
change our brains is not new.

What is new is the knowledge of how drugs change the brain to cause it
to become addicted. Research in this field has uncovered some new and
interesting discoveries.

As I discussed in an earlier column, addicted individuals exhibit
certain qualities.

For example, an addicted person experiences a compulsion to take the
substance; an increased tolerability to the substance over time;
persistent use even though it is harmful; progressive neglect of other
enjoyable activities; and withdrawal symptoms. But what brain
mechanisms are involved in these reactions?

New research conducted at the National Institute on Drug Abuse in the
US has discovered that the brain dopamine system is central in addiction.

Imaging studies using MRI and PET scans show that almost every drug of
abuse (including nicotine, alcohol, cannabis, cocaine, heroin and
methamphetamine) elevates the level of the chemical dopamine in the
brain.

Dopamine is a neurotransmitter involved in attention, memory and
pleasure-reinforcing behaviour.

Levels of dopamine increase in response to natural rewards such as
food and sex and also in response to stress. It is part of what is
known as a reward circuit in the brain.

Addictive drugs stimulate the dopamine system in extreme amounts and
usually cause a release of five to 10 times the amount of dopamine as
natural rewards. Repeated excessive stimulation of these reward
circuits is what causes addiction.

Eventually, the individual's brain becomes altered to the point that
natural rewards are no longer sufficient.

Judgment and decision-making circuits become damaged and the
individual is reduced to an overwhelming need to seek and take drugs.

Not only is the dopamine release increased with initial drug use, but
after chronic drug abuse and during withdrawal, the number of dopamine
receptors in the brain decreases.

This involves dysfunction in the prefrontal regions of the brain and
results in decreased sensitivity to things that cause natural reward
stimulation.

In fact, the numbers of dopamine receptors remain low even after
months of abstinence from drugs.

Decreased sensitivity and receptor levels are probably a consequence
of conditioned learning in the brain and the resetting of reward
thresholds in order to adapt to the abnormally high levels of
stimulation induced by the abused drugs.

Genetics also play an important role in drug addiction. It has always
been clear that some people are more susceptible to addiction than
others.

Although everyone experiences a pleasurable sensation from
intoxication, not everyone becomes addicted to the intoxicating substance.

High levels of dopamine receptors are protective against addiction.
Individuals born with higher numbers of these receptors may be less
likely to become addicted. This is probably because, according to
research, the subjective response to drugs of abuse is more pleasant
with lower numbers of dopamine receptors.

Having higher levels of receptors means that the drugs are not as
pleasant and do not stimulate as much of a reward reaction in the brain.

While genetics is one factor involved in addiction, some environmental
situations can also bring about an increased likelihood that abuse
will lead to addiction.

Studies in animals show animals that are dominant in their social
groups increase the levels of dopamine receptors in their brains.

More research into humans is necessary, but this finding may explain
how poverty, abuse and neglect are related to an increased likelihood
of addiction at the neurochemical level. As research in this field
continues, more will be discovered about the mechanisms in the brain
that are affected by drug abuse.

Once the disease of addiction is better understood, effective
treatment will be easier to administer and new strategies will be developed.

In the meantime, if you or someone you love experiences a substance
abuse problem, seek help. Your doctor can recommend treatment programs
and support groups. Although addiction is a disease, it is not
impossible to overcome.