THE speci®city of the Wisconsin Card Sorting Test (WCST) for assessing frontal lobe pathology remains controversial, although lesion and cerebral blood ¯ow studies continue to suggest a role for the dorsolateral prefrontal cortex in WCST performance.Inconsistencies might derive from the extended use of various WCST scores as equivalent indicators of frontal pathology.In this study, event-related potentials (ERPs) were recorded from 32 normal subjects who committed perseverative and non-perseverative errors.Both types of WCST errors evoked anomalous but distinct ERP patterns over frontal lobe regions.Perseverative errors were also associated with a dysfunctional extrastriate response to stimulation.This evidence suggests that perseverative and non-perseverative errors result from disruptions in two different prefrontal neural networks engaged during card sorting.