More Brain Glucose Metabolism During Abstinence Does Not Necessarily Mean Better Performance

Brain glucose metabolism increased during early methamphetamine abstinence in a small PET study, but that increase was not a direct measure of cognitive recovery. The study illustrates why biological change and improved function must be evaluated separately.

Repeated scans in the same people

Berman and colleagues studied 10 methamphetamine-dependent participants after five to nine days of abstinence and again after four additional weeks of supervised abstinence. Twelve healthy comparisons were tested at corresponding intervals. Positron-emission tomography used fluorodeoxyglucose, or FDG, during a vigilance task.

The tracer measured metabolism

The FDG signal indexed regional cerebral glucose metabolism. It was not a measurement of methamphetamine, amphetamine or dopamine. Reported metabolism increased in cortex, particularly parietal regions, while subcortical metabolism did not show corresponding changes. Global scaling also matters: a region’s relative activity can decrease when the overall reference increases.

The behavioral findings were more limited

The investigators did not establish a significant group-by-session interaction for vigilance accuracy or average reaction time. Variability in reaction-time change was greater in the methamphetamine group. Accordingly, an increase in metabolism should not be described as a demonstrated parallel improvement in attention.

A small mechanistic study, not an individual diagnostic rule

Repeated imaging strengthens evidence that physiology changed over time, but the small selected sample limits generalization and causal explanations. Cortical-subcortical balance, mood and task behavior can relate in complex ways. No blood, urine or oral-fluid stimulant concentration was validated as a predictor of PET recovery or safe driving. The supported conclusion is a change in measured glucose metabolism during the observed abstinence interval, with behavioral and interpretive limitations retained.

Related evidence

For a different perspective on interpreting stimulant evidence, see our analysis of the Swedish amphetamine concentration study. Its study population and outcome should remain separate from the present findings.

Primary research

Changes in Cerebral Glucose Metabolism during Early Abstinence from Chronic Methamphetamine Abuse. Original human research. doi:10.1038/sj.mp.4002107.