Switching strategy underlies phonemic verbal fluency impairment in obsessive–compulsive disorder Ye Seul Shin a , Na Young Shin b , Joon Hwan Jang c , Geumsook Shim c , Hye Yoon Park c , Min-Sup Shin d , Jun Soo Kwon a,b,c,n a Department of Brain & Cognitive Sciences, World Class University Program, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea b Interdisciplinary Cognitive Science Program, Seoul National University, Seoul, Republic of Korea c Department of Psychiatry & Behavioral Sciences, Seoul National University College of Medicine, 101 Daehak-ro, Jongno-gu, Seoul 110-744, Republic of Korea d Department of Child-Adolescent Psychiatry, Seoul National University College of Medicine, Seoul, Republic of Korea article info Article history: Received 9 October 2011 Received in revised form 13 April 2012 Accepted 4 July 2012 Available online 16 July 2012 Keywords: Obsessive–compulsive disorder Phonemic verbal fluency Switching Executive dysfunction Frontal-striatal circuitry Symptom dimensions 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-naı ¨ve 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. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction Recently, a growing number of neuropsychological and neu- roimaging studies have shown that neurobiological abnormalities in the frontal-subcortical circuits play an essential role in the pathophysiology of obsessive–compulsive disorder (OCD) (Kwon, Jang, Choi, & Kang, 2009). This neurobiological model is consistent with neuropsychological findings suggesting a deficit in several cognitive domains in OCD including visual memory, verbal fluency, and executive function. Verbal fluency is a widely used neuropsychological measure that assesses the spontaneous oral generation of words based on phonemic (phonemic fluency) or semantic criteria (semantic flu- ency). In general, phonemic fluency has been thought to be associated with frontal-lobe dysfunction, while semantic fluency has been thought to be associated with temporal-lobe dysfunction; thus, patients with frontal lobe lesions show impaired phonemic fluency, while their semantic fluency remains relatively intact (Troyer, Moscovitch, Winocur, Alexander, & Stuss, 1998). Optimal performance in verbal fluency tasks requires two different, but complementary, cognitive components: clustering and switching (Troyer, Moscovitch, & Winocur, 1997). Clustering, generating words within subcategories, depends on temporal lobe processes, such as verbal memory and verbal storage. Switching, the ability to shift between clusters, relies on frontal lobe processes such as mental set shifting, cognitive flexibility, and strategic search. In particular, previous studies have consistently reported that switch- ing ability is critical for optimal phonemic fluency (Troyer et al., 1997, 1998) and impaired switching performance underlies poor verbal fluency in patients with frontal lobe lesions, such as schizophrenia (Kosmidis et al., 2005; Moore, Savla, Woods, Jeste, & Palmer, 2006), HIV/AIDS (Millikin, Trepanier, & Rourke, 2004), and depression (Fossati, Guillaume Le, Ergis & Allilaire, 2003). Several studies of phonemic verbal fluency have reported impairment in obsessive–compulsive disorder (OCD) (Choi et al., 2004; Christensen, Kim, Dysken, & Hoover, 1992; Schmidtke, Schorb, Winkelmann, & Hohagen, 1998; Shin et al., 2008), but Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jocrd Journal of Obsessive-Compulsive and Related Disorders 2211-3649/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jocrd.2012.07.005 n Corresponding author at: Department of Psychiatry & Behavioral Sciences, Seoul National University College of Medicine, 101 Daehak-ro, Jongno-gu, Seoul 110-744, Republic of Korea. Tel.: þ82 2 2072 2972; fax: þ82 2 747 9063. E-mail address: kwonjs@snu.ac.kr (J.S. Kwon). Journal of Obsessive-Compulsive and Related Disorders 1 (2012) 221–227