Impaired retrieval of semantic information in bipolar disorder: a clustering analysis of category-fluency productions

On category-cued verbal fluency tasks, such as animal naming, respondents often report exemplars in semantically related clusters. We (Sung et al., 2012) used this tendency to elucidate sources of semantic dysfunction in adults with schizophrenia (SZ). Many patients with bipolar disorder (BD) show cognitive deficits that are similar to but milder than those seen in SZ. Whether this similarity extends to the functioning of the semantic system is unclear. To test the hypothesis that it does, we adapted a clustering technique called singular value decomposition (SVD) to investigate the clustering pattern of semantic retrieval in BD. Two category-fluency tasks (animal and supermarket-item naming) were administered to 98 adult outpatients with BD and 98 healthy adults (NC) who matched the BD group in age, sex, education, and estimated premorbid IQ. Results of clustering analysis showed that patients with BD produced less coherent category clusters than healthy adults. Specifically, patients with BD showed less coherent clusters of low-frequency animal names, but their overall productivity was not more impaired than the NCs'. In the supermarket condition, patients not only showed incoherent clustering of named supermarket items regardless of their frequencies, but also produced smaller numbers of exemplars than NCs did. The semantic system abnormalities shown by adults with BD were similar to those we found previously in persons with SZ, although the group differences were smaller. Overall, these results point to a concept retrieval/access deficit in BD and underscore the importance of analyzing the content of category-fluency productions.