High Price

had outperformed methamphetamine addicts on a few tests, the performance of the two groups wasn’t different on the majority of tests. More important, when I compared the cognitive scores of the methamphetamine addicts in the Simon study against scores in a larger normative dataset, none of the methamphetamine users’ scores were outside the normal range. 8 This meant that the cognitive functioning of the methamphetamine users was normal. This should have tempered the researchers’ conclusions and prevented them from stating such dire warnings. What’s more, the methamphetamine literature was filled with similar unwarranted conclusions; as a result, the apparent methamphetamine addiction–cognitive impairment link has been widely publicized—numerous articles have appeared in scientific journals and the popular press.
    The reporting of brain imaging findings has been especially misleading. On July 20, 2004, for example, the New York Times printed an article titled, THIS IS YOUR BRAIN ON METH: A “FOREST FIRE” OF DAMAGE. It stated, “People who do not want to wait for old age to shrink their brains and bring on memory loss now have a quicker alternative—abuse methamphetamine . . . and watch the brain cells vanish into the night.” This conclusion was based on a study that used magnetic resonance imaging (MRI) to compare brain sizes of methamphetamine addicts with non-drug-using healthy people. 9 The researchers also looked at the correlation between memory performance and several brain structural sizes. They found that methamphetamine users’ right cingulate gyrus and hippocampus were smaller than those of controls by 11 and 8 percent, respectively. Memory performance on only one of four tests was correlated with hippocampal size (that is, individuals with larger hippocampal volume performed better). As a result, the researchers concluded, “chronic methamphetamine abuse causes a selective pattern of cerebral deterioration that contributes to impaired memory performance.” This interpretation, as well as the one printed in the Times article, is inappropriate for several reasons.
    First, brain images were collected at only one time point for both groups of participants. This makes it virtually impossible to determine whether methamphetamine use caused “cerebral deterioration,” because there might have been differences between the groups even before methamphetamine was ever used. Second, the non–drug users had significantly higher levels of education than methamphetamine users (15.2 versus 12.8 years, respectively); it is well established that higher levels of education lead to better memory performance. Third, there were no data comparing methamphetamine users with controls on any memory task. This, in itself, precludes the researchers from making statements regarding impaired memory performance caused by methamphetamine. Nonetheless, the only statistically significant cognitive finding was a correlation of hippocampal volume and performance on one of the four tasks. This finding is the basis for the claim that methamphetamine users had memory impairments, because the hippocampus is known to play a role in some long-term memory; but other brain areas are also involved in processing long-term memory. The size of these other areas was not different between the groups. Finally, the importance on everyday functioning of the brain differences is unclear because an 11 percent difference between individuals, for example, is most likely within the normal range of brain structure sizes.
    This example is not unique. The brain imaging literature is replete with a general tendency to characterize any brain differences as dysfunction caused by methamphetamine (as well as other drugs), even if differences are within the normal range of human variability. 10 It would be like comparing the brains of police officers who have less education with those of college professors who have obtained a PhD, and concluding that the officers are cognitively impaired as a result of any differences that might be noted. This simplistic thinking is the main thrust behind the notion that drug addiction is a brain disease. It certainly isn’t a brain disease like Parkinson’s disease or Alzheimer’s disease. In the case of these illnesses, one can look at the brains of affected individuals and make pretty good predictions about the illness involved. We are nowhere near being able to distinguish the brain of a drug addict from