Brain scans reveal tobacco addiction mechanism
express the desire to stop, and although many receive extensive treatments, fewer
than half succeed in stopping long term. It has long been known that nicotine is
highly addictive, but only recently have the specific mechanisms causing addiction
Researchers at the University of California,
Los Angeles, led by Dr. Arthur L. Brody, used brain imaging to study the brain-receptor
nicotine occupation level needed to avoid symptoms of withdrawal. The results were
published in the August issue of Archives of General Psychiatry.
They conducted tests after subjects
had refrained from tobacco use for two days, taking PET images using a radiotracer.
The number of cigarettes the patients consumed varied. Nicotine levels and withdrawal
symptoms were monitored throughout the study.
In subjects who smoked during the study,
nicotine replaced the radiotracer in amounts dependent on the level consumed. The
brain scans specifically showed that the level of nicotine binding was highest in
the thalamus, the brain stem and the cerebellum. The images showed that typical
daily smokers must maintain 88 to 95 percent brain receptor occupancy to avoid cravings.
Two and a half hours after some trial subjects were given one cigarette, their receptor
occupancy was still at 90 percent, but they felt a presmoking craving.
Subjects given one or more cigarettes
felt relief of cravings, but those given less than one cigarette during their scans
did not have a complete abatement of their cravings. The study’s findings
were consistent with the idea that smokers desensitize their nicotine receptors
and continue to smoke to avoid having receptors that are free of nicotine.
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