A rat study found greater attention improvement among poorer baseline performers after low-dose amphetamine. Associations with striatal chemistry supported a mechanistic hypothesis, not a validated method for selecting human treatment.
Turner and colleagues trained rats on a signal-detection task with varying signal durations, then tested saline and amphetamine at 0.1 and 0.25 mg/kg. They also analyzed monoamine content and gene expression in prefrontal and dorsal-striatal tissue. The work combined behavioral response differences with laboratory tissue measurements; those measurements were not human blood biomarkers.
At 0.1 mg/kg, poorer performers improved toward the accuracy of higher performers. Baseline accuracy related to the magnitude of change. Poorer performance was also associated with higher striatal homovanillic acid and 5-hydroxyindoleacetic acid, while dopamine-transporter gene expression correlated with baseline accuracy. Comparable prefrontal changes were not found. The regional null finding matters to a claim about where the association occurred.
Baseline grouping and change scores require caution, and a tissue association cannot prove that the measured chemical difference caused the drug response. These metabolites are not synonyms for directly measured moment-to-moment transmitter release. The experiment also cannot establish that every low-performing person will benefit from amphetamine or provide a clinical concentration target. Species, task, dose and route constrain translation. The study supports investigating striatal contributions to individual differences, while prospective human prediction and treatment recommendations require separate evidence.
See baseline-defined subgroups and regression-to-the-mean concerns in humans.