Generally speaking, potheads don't have a reputation for clarity
of mind, but a new study finds that those who begin partaking
when they're under 16 ar even more likely than late adopters to
perform badly on cognitive tests. Staci Ann Gruber of Harvard
Medical School, who conducted the research, presented her
conclusions at Monday's annual meeting for the Society for
Neuroscience. Here's the short version:  How did the study work?
Gruber recruited 35 "chronic marijuana smokers" and 29 non-
smokers. Of the first group, 20 people began smoking before the
age of 16, and the other afterward; 16 was chosen as a cutoff
point, says Gruber, because "that's when teens tend to [begin
to] use drugs." The participants (whose age averaged 22) were
asked to perform a series of brain exercises such as the
Wisconsin Card Sort Task — a cognitive test that involves
categorizing cards according to shape, color, and other factors.
What did the study find? The pot smokers performed worse than
the control group — making repeated e