Impairment of the semantic network in schizophrenia

It is well established that patients with schizophrenia display a variety of language impairments. Despite considerable research, however, the underlying mechanisms of the language deficits in schizophrenia remain unclear. Representations of semantic networks of 56 patients with schizophrenia and 28 normal comparison (NC) subjects of similar ages and educational levels were generated by multidimensional scaling and Pathfinder analyses of their responses on the Animal Fluency Test. On the basis of traditional scoring techniques (i.e., total number of correct animal names generated in 60 s), all patients performed significantly worse than the NC subjects. More detailed analyses of the underlying semantic networks revealed that performance in the patients varied according to age of onset and subtype of schizophrenia. The semantic network of patients with late-onset schizophrenia (i.e., with onset after age 45) was virtually identical to that of the NC group. In contrast, the semantic network of patients with a younger age of onset was disorganized and differed significantly from that of the NC subjects. Findings demonstrated that patients with nonparanoid subtypes displayed greater disorganization in their semantic networks than patients with a paranoid subtype. Although general fluency impairments (e.g., difficulties in initiation, retrieval, and search mechanisms) may be sensitive to schizophrenia, per se, specific deficits in the structure of semantic knowledge may be associated with certain characteristics of individual patients with schizophrenia, such as an earlier age of onset and nonparanoid subtype.