Verbal fluency, clustering, and switching in PFTBI

Background: Verbal fluency in patients with psychosis following traumatic brain injury (PFTBI) was reported by Fujii et al. (2004) to be comparable to healthy participants. This finding is counterintuitive given the prominent fluency impairments demonstrated post traumatic brain injury and in schizophrenia. Methods: Phonological fluency ('F' 'A' and 'S'), and semantic fluency (fruits and vegetables) were assessed in four matched groups; PFTBI (N=10), TBI (N=10), schizophrenia (N=23), and healthy controls (N=23). Clustering and switching during fluency responses were determined by two independent raters. Results: PFTBI patients showed the lowest mean production of words across all assessments of verbal fluency, and all groups illustrated greater semantic, relative to phonological, fluency. No group-wise differences were shown to the number of clusters, or mean cluster size, produced for either fluency trial. However, the PFTBI patients demonstrated the least number of switches between clusters than any other group on both fluency trials. Conclusions: Reduced fluency from PFTBI patients is aligned with existing evidence in TBI and schizophrenia. Data further suggested that PFTBI patients share deficits with their single diagnosis counterparts. Phonological fluency deficits may thus primarily stem from the consequences of the injury (i.e., executive dysfunction), while semantic fluency deficits may stem from the effects of the psychosis. Finally, novel evidence was obtained for concise executive function impairment in PFTBI using switching analysis, with results indicating that patients were unable to efficiently move to a new cluster subcategory once the present cluster was exhausted