Executive inhibition and semantic association in schizophrenia

Research indicates that some patients with schizophrenia display aberrant inhibition of semantic memory, which may underpin formal thought disorder (FTD). We administered a novel Stroop-like paradigm to three groups of participants: 15 schizophrenic patients with formal thought disorder (FTD), 16 with low FTD ratings, and 15 healthy matched controls. They were required to inhibit a prepotent response for a (previously instructed) required response. Four conditions examined the effect of executive demands by manipulating the relatedness between prepotent and required responses (i.e., identical, semantically related, or unrelated). Two further conditions examining executive function working memory demands required the naming of real or abstract pictures that did and did not necessitate inhibition, respectively. Patients with and without FTD experienced increased difficulty when executive function working memory was required. Moreover, those with FTD also showed increased executive inhibition, but the pattern of errors suggested that the result of this was an automatic activation of semantically related representations. The findings support the notion that increased inhibition underpins the disorganised access to semantic memory in patients with FTD.