Switching strategy underlies phonemic verbal fluency impairment in obsessive–compulsive disorder

Abstract

Previous studies have reported verbal fluency impairment in obsessive–compulsive disorder (OCD), but no study has evaluated the cognitive processes underlying verbal fluency in OCD. In the present study, we sought to test the hypothesis that phonemic fluency impairment in OCD resulted from switching problems rather than lack of fluency per se. In addition, we aimed to evaluate whether certain symptom dimensions were associated with impaired phonemic fluency to better understand OCD heterogeneity. The study included 85 patients with OCD (45 drug-naïve and 40 drug-free) and 71 healthy controls matched for gender, age, education, and intelligence. The Controlled Oral Word Association (COWA) test was administered to assess phonemic fluency and switching performance. Patients with OCD generated a smaller number of words and displayed fewer switches than did healthy control subjects, and switching was found to mediate impaired phonemic fluency in OCD. Furthermore, impairment in switching and phonemic fluency was related to the symmetry dimension in patients with OCD. Our findings suggest that phonemic fluency impairment in OCD is mediated by a switching deficit that may originate from abnormal processing in the frontal-striatal circuitry involving the orbitofrontal cortex. Moreover, different obsessive–compulsive symptom dimensions may be characterized by distinct neurocognitive dysfunctions in OCD.