Similar Balloon Choices Can Conceal Different Brain Responses in Methamphetamine Research

A methamphetamine-dependence imaging study found differences in brain responses as risk increased, even though average balloon pumping did not significantly differ between groups. The task’s behavioral measure and its neural correlates answered different questions.

What counted as risk in the experiment

Kohno and colleagues studied 25 methamphetamine-dependent participants and 27 controls using functional MRI during a Balloon Analogue Risk Task and at rest. Participants chose whether to keep pumping a virtual balloon or cash out. Pump count indexed increasing potential reward and risk within that artificial task.

The imaging result concerned changing demands

Activation changed with pump number differently across groups: modulation was stronger in ventral striatum and weaker in right dorsolateral prefrontal cortex among methamphetamine-dependent participants. Resting-state connectivity also differed in selected circuits and related to task activation. These findings support hypotheses about circuit balance rather than a direct chemical measurement of reward processing.

Average pumps were not significantly different

The detailed behavioral analysis did not find a significant difference in average pumps before cashing out. Other performance measures, including overall performance, were not interchangeable with pump count. It would therefore be misleading to summarize every result as simply more risk taking.

Limits of the mechanistic interpretation

The case-control design cannot establish whether the circuit pattern preceded drug use or resulted from it. The authors also note that the task’s timing did not fully isolate evaluation, selection and anticipation. Urine testing supported study procedures; it did not create a concentration-based impairment rule. Neither brain connectivity nor balloon pumping was validated as an individual real-world driving-risk test.

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

Risky Decision-making: Prefrontal Function and Mesocorticolimbic Resting-state Connectivity in Methamphetamine Users. Original human research. doi:10.1001/jamapsychiatry.2014.399.