Building meaning in schizophrenia

Abstract

The schizophrenia syndrome is clinically characterized by abnormal constructions of meaning during comprehension (delusions), perception (hallucinations), action (disorganized and non-goal-directed behavior) and language production (thought disorder). This article provides an overview of recent studies from our laboratory that have used event-related potentials and functional magnetic resonance imaging to elucidate abnormalities in temporal and spatial patterns of neural activity as meaning is built from language and real-world visual events in schizophrenia. Our findings support the hypothesis that automatic activity across semantic memory spreads further within a shorter period of time in thought-disordered patients, relative to non-thought-disordered patients and healthy controls. Neuroanatomically, increased activity to semantic associates is reflected by inappropriate recruitment of temporal cortices. In building meaning within sentences, the fine balance between semantic memory-based mechanisms and semantic-syntactic integration (dictating "who does what to whom") is disrupted, such that comprehension is driven primarily by semantic memory-based processes. Neuroanatomically, this imbalance is reflected by preserved (and sometimes increased) activity within temporal and inferior prefrontal cortices, but abnormal modulation of dorsolateral prefrontal and parietal cortices. In building meaning across sentences (discourse), patients fail to immediately construct coherence links, but may show inappropriate recruitment of temporal and inferior prefrontal cortices to incoherent discourse, again reflecting inappropriate semantic memory-based processing (abnormal inferencing). Finally, these abnormalities may generalize to real-world visual event comprehension, where patients show reduced neural activity in determining relationships around goal-directed actions, and comprehension is again dominated by semantic memory-based mechanisms.