Smoking causes long-term but reversible effects to the brain


Does smoking change the human brain?, writes Dr Muiris Houston.

Cigarette smoking causes long-lasting but reversible effects to the human brain, the conference was told.

Dr Nora Volkow, of the National Institute of Drug Abuse at the US National Institute of Health, described research which showed that the concentration of an enzyme in parts of the brain was much reduced in smokers.

The enzyme's normal function is to break down a brain chemical called dopamine. As a result of this enzyme's lower levels in the brain, the activity of dopamine - which reinforces addictive behaviour in humans - is increased.

According to Dr Volkow, this enhances the effect of nicotine in the brains of smokers. "It takes three months after stopping smoking for the enzyme levels to get back to normal," she said.

An examination of the brains of smokers at post-mortem shows an increase in the number of nicotine receptors. This illustrates nicotine's ability to alter the number of receptors for the drug in the brain, thus reinforcing the effects of smoking, said Dr Volkow.

She also described separate research involving magnetic resonance imaging techniques, which shows the brain "lighting up" under the influence of nicotine.

"If smokers are denied nicotine, then they show evidence of sub-normal cognitive functioning," she told the conference.

Dr Jack Henningfield, of Johns Hopkins Medical School in the US, said that after the brain has changed, smokers need nicotine to maintain normal function. He described how US tobacco companies had worked to improve the design of cigarettes from an old-fashioned "scatter gun" approach to a design that ensured all the molecules of tar and nicotine hit their target in the lung.