Qualitative analysis of verbal fluency before and after unilateral pallidotomy

This study examined qualitative aspects of phonemic and semantic fluency before and after unilateral pallidotomy in patients with intractable Parkinson's Disease (PD). Specifically, clustering (number of similar words generated sequentially) and switching (number of changes or switches from one cluster to another) were evaluated for both fluency tasks. Twenty-five PD patients participated and were grouped according to whether they improved or declined on each of the fluency measures after surgery. Decliners evidenced decreased switching, but not clustering, suggesting difficulties with set-shifting and cognitive flexibility rather than a diminished semantic store of information or retrieval difficulties. Though consistent with hypotheses about difficulties with executive processing after pallidotomy, a series of correlational analyses with composite measures of neuropsychological functioning (attention, language, executive processing, and memory) suggest caution in interpreting these findings. In these analyses, clustering was not meaningfully related to any of the composites whereas switching was significantly and positively related to the composites; this pattern emerged, for the most part, on both fluency measures before and after surgery. Switching, but not clustering, was also significantly and positively correlated with total words generated on both semantic and phonemic fluency. Switching changes across time were also related to DRS changes post-pallidotomy. These correlational analyses challenge the specificity of the switching variable and, more broadly, the validity of these qualitative measures of verbal fluency.