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 "Earlier studies of older participants showed that
the smokers had structural differences in various brain regions,"
said senior author Edythe D. London.
And in studies of adolescent animals, nicotine damaged and killed
brain cells, added London, from the Semel Institute for Neuroscience
and Human Behavior at UCLA and the David Geffen School of Medicine
in Los Angeles.
"While the results do not prove causation, they suggest that there
are effects of cigarette exposure on brain structure in young
smokers, with a relatively short smoking history," London said.
She and her team at UCLA mapped the brains of 42 people ages 16 to
21 using magnetic resonance imaging (MRI) and asked them about their
smoking history and cravings.
Eighteen of the participants were smokers. They had typically
started smoking around age 15 and smoked six to seven cigarettes per
day.
There were no clear differences in the brains of smokers versus
non-smokers. However, among smokers, those who reported smoking more
cigarettes tended to have a thinner insula, a region of the cerebral
cortex involved in decision making, according to results published
in the journal Neuropsychopharmacology. The effects seemed confined
to the right insula.
Previous studies have suggested the insula plays a central role in
tobacco dependence, with the highest density of nicotine receptors
in the brain.
The researchers also found a thinner insula in the brains of people
who had more cravings and felt more dependent on cigarettes. Their
study was funded by Philip Morris USA, makers of Marlboro and
Virginia Slims.
Young people ages 18 to 25 have the highest smoking rates in the
U.S. at 30 percent, London said.
"Because the brain is still undergoing development, smoking during
this critical period may produce neurobiological changes that
promote tobacco dependence later in life," she said. Changing the
structure of the insula may affect future smoking dependence and
other substance abuse.
"It is possible that changes in the brain from prolonged exposure
help maintain dependence," she said.
People who start smoking early in life seem to have more trouble
quitting and have more serious health consequences than those who
start later, London said.
But since the study only assessed smokers at one point in time, it
doesn't prove that cigarettes changed their brains.
"It is possible that such changes pre-dated the smoking, i.e. they
were not caused by smoking," Dr. Nasir H. Naqvi told Reuters Health
in an email. "The only way to know this is to take a group of
adolescents who have never smoked, follow them over time, and then
see who starts smoking, and then compare them to the adolescents who
never started smoking."
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Naqvi, a substance abuse researcher at Columbia
University in New York City, was not involved in the study.
He studies the insula and said that area drives drug addiction like
a "gas pedal" and also controls decision making like a "brake
pedal."
Since the insula was thinner in heavier smokers, it could be they
have reduced power over the "brake pedal" and less control over
cravings, he said.
"The key question is whether these changes are reversible with
smoking cessation, or whether they persist," Naqvi said. But few
studies have measured changes in the brains of people who stop
taking a drug.
"What we do know is that once you are addicted to smoking, you will
always have a high likelihood of relapse, even if you are abstinent
for many years," Naqvi said. The study is interesting
but quite small, especially for a study on this age group, Simone
Kuhn said.
Kuhn studies brain plasticity across the lifespan at the Max Planck
Institute for Human Development in Berlin and was not involved in
the new research.
"Between 16 and 21 the prefrontal cortex changes considerably; this
might make research such as this slightly difficult," she told
Reuters Health. "Though I clearly agree that brain structural
effects of smoking in adolescence is an extremely interesting topic
that could be used to spice up anti-smoking campaigns, addressing
this age group with scientific facts."
"It would be useful to do this kind of study in a larger number of
people, starting before the initiation of smoking and continuing
with repeated scans," London said. "This is practical. It just
requires funding." ___
Source: http://bit.ly/1kNxlHz
Neuropsychopharmacology, online March 3, 2014.
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