Cognitive flexibility in neurological disorders: Cognitive components and event-related potentials

Performance deficits on the Wisconsin Card Sorting Test (WCST) in patients with prefrontal cortex (PFC) lesions are traditionally interpreted as evidence for a role of the PFC in cognitive flexibility. However, WCST deficits do not occur exclusively after PFC lesions, but also in various neurological and psychiatric disorders. We propose a multi-component approach that can accommodate this pattern of omnipresent WCST deficits: the WCST is not a pure test of cognitive flexibility, but relies on the effective functioning of multiple dissociable cognitive components. Our review of recent efforts to decompose WCST performance deficits supports this view by revealing that WCST deficits in different neurological disorders can be attributed to alterations in different components. Frontoparietal changes underlying impaired set shifting seem to give rise to WCST deficits in patients with amyotrophic lateral sclerosis, whereas the WCST deficits associated with primary dystonia and Parkinson's disease are rather related to frontostriatal changes underlying deficient rule inference. Clinical implications of these findings and of a multi-component view of WCST performance are discussed.