YOUNG MARIJUANA USERS PAY COGNITIVE PRICE

Marijuana smoking often starts in adolescence - and the timing could
not be worse, a new study suggests.

Young adults who started using the drug regularly in their early
teens performed significantly worse on tests assessing brain function
than did subjects who were at least 16 when they started, scientists
reported last week.

The findings led researchers at McLean Hospital to surmise that the
developing teenage brain may be particularly vulnerable to the ill
effects of marijuana.

"We have to understand that the developing brain is not the same as
the adult brain," said Dr. Staci A. Gruber, the paper's senior author
and director of cognitive and clinical neuroimaging at McLean, a
Harvard-affiliated hospital in Belmont, Mass.

The study, done in conjunction with brain scans, was small,
consisting of 35 chronic marijuana smokers who were 22 years old on
average. The subjects were asked to complete an assessment of
executive function - the brain processes responsible for planning and
abstract thinking, as well as understanding rules and inhibiting
inappropriate actions. The test - in which participants were asked to
sort cards with different shapes, numbers and colors - is a measure
of cognitive flexibility.

At 15, Dr. Gruber said, the brain is still changing, and "the part
that modulates executive function is the last part to develop."