Amphetamine increased willingness to keep working in a human effort task without changing the proposed parietal-alpha EEG marker. A measure that tracks task engagement need not track the drug-induced change in behavior.
Noback and colleagues tested 23 healthy adults in a double-blind placebo comparison using a progressive-ratio breakpoint task with EEG. Breakpoint marks the point at which a participant stops responding as the required work increases. Mouse experiments examined related behavior with and without concurrent EEG recording. These were controlled human and animal experiments, with species-specific procedures.
Human breakpoint increased after amphetamine, while parietal alpha power was unchanged by the drug. Alpha power rose as participants approached breakpoint, replicating an engagement-related pattern. The mouse findings were more complicated: 1 mg/kg decreased breakpoint during EEG recording, whereas 0.3 mg/kg increased breakpoint in a separate cohort without EEG. The human direction should not be assigned to every mouse dose or recording condition.
The authors identified recording equipment as a possible influence requiring further study. Dose, cohort and measurement conditions could not be treated as interchangeable. Increased breakpoint is an operational measure of effort under specified incentives; it does not establish improved reasoning, productivity or treatment of low motivation in illness. The unchanged EEG finding also prevents treating alpha power as a direct readout of amphetamine-induced effort. This is a useful dissociation between behavior and a candidate biomarker, rather than evidence that either measure captures every aspect of motivation.
See effort allocation without improved reward learning.