Effects of neuroleptic medications on speech disorganization in schizophrenia: biasing associative networks towards meaning

Background. While some cognitive accounts of disorganized speech, or though t disorder, in schizophrenia have emphasized failures in working memory/dis course planning or selective attention, we have suggested that thought diso rder resides in the semantic system. In this study we assessed the effect o f neuroleptic medication on thought disorder and semantic processing. Methods. Seventeen patients with schizophrenia were assessed while receivin g neuroleptic medications and in crossover fashion, placebo. A number of me asures were obtained: clinically rated thought disorder (using the Thought, Language and Communication Scale); working memory (letter number span); le xical integrity (naming and receptive vocabulary); and, semantic priming of intracategorical word pairs. Results. Semantic priming measures improved with neuroleptic medication, as did clinically rated thought disorder. No other measure changed significan tly. Priming selectively covaried with changes in thought disorder. Conclusion. Changes in spreading semantic activation, measured in a semanti c priming paradigm and presumably brought about by neuroleptics' influence on dopaminergic neuromodulatory systems, might reflect changes in the biase s of pre-existing associative networks that favour or increase the accessib ility of representations related by shared features. This study also has im plications for the architecture of normal language in that a dissociation b etween the lexical and semantic levels was observed, due to the selective c ompromise of tasks demanding semantic processing.