Amphetamine altered EEG measures differently during easy and difficult trials. A single statement that the drug increased brain activity would miss the conditional nature of the findings.
Bhakta and colleagues studied 23 healthy adults in a randomized double-blind placebo-controlled within-subject experiment. Participants received 10 mg, 20 mg d-amphetamine and placebo across separate sessions. They performed a difficulty-modulated five-choice continuous-performance task while EEG recorded electrical responses. The design distinguished target responses from correctly withholding responses to non-targets.
The drug increased signal-detection performance, sped reaction time and increased frontal P3a amplitude during correct non-target rejections. Other effects depended on demand. During easy target trials, frontal theta power was suppressed; during difficult target trials, drug-related P3b changes correlated with improvements in hit rate. Those are different electrical features, not interchangeable measures of overall activation. A correlation with behavioral change does not establish that changing the EEG feature caused the performance benefit.
The small healthy-volunteer sample was used to investigate candidate physiological measures, not to validate a clinical prediction tool. EEG records scalp electrical activity and does not quantify amphetamine concentration or determine individual driving impairment. Findings under one task difficulty cannot be assigned automatically to a different environment. The investigators proposed further testing in populations with cognitive-control deficits; benefit in those patients was not demonstrated by this healthy-participant study. Its contribution is showing that task demand and response type can change the meaning of a drug-related brain signal.
See resting EEG parameters and their diagnostic limitations.