Fluid Intelligence and Executive Dysfunction in Progressive Supranuclear Palsy.

BACKGROUND: Fluid intelligence (g) contributes to executive-task performance, but its role in progressive supranuclear palsy (PSP) remains unclear. OBJECTIVES: To examine whether executive deficits in PSP are explained by reductions in g. METHODS: Thirty-five PSP patients, 39 Parkinson's disease (PD) patients and 18 healthy controls underwent neuropsychological assessment. G was derived using principal component analysis from non-executive cognitive measures. Group differences in executive performance were examined before and after controlling for g. Healthy controls provided contextual comparison. RESULTS: In PSP versus PD, differences in phonemic fluency and TMT-B were no longer significant after controlling for g, whereas WCST categories remained significant. In PSP versus healthy controls, WCST and phonemic fluency remained significant after controlling for g. Sensitivity analyses in cognitively preserved participants showed similar results. CONCLUSIONS: Executive deficits in PSP are partly associated with reduced g, but cognitive flexibility appears to reflect an additional disease-related impairment.