What can Event-related Potentials tell us about language, and perhaps even thought, in schizophrenia?

Abstract

Disturbances of thought and language are fundamental to schizophrenia. Cognitive behavioral and electrophysiological research has implicated problems in two different neurocognitive mechanisms: abnormalities in the structure and function of semantic memory, and abnormalities in combining and integrating words together to build up sentence and discourse context. This review discusses recent electrophysiological evidence suggesting that these two deficits are not completely distinct, but rather that language impairment in schizophrenia results from a dysfunctional interaction between these systems in an effort to build up higher-order meaning. Moreover, although language abnormalities are more pronounced in patients with positive thought disorder, they manifest themselves in all patients when increased demands are placed on the comprehension system. Further investigation of language dysfunction may also provide insights into other aspects of psychotic thought.

Figure 1

Left: Under automatic experimental conditions, in the absence of any behavioral response requirement to trials of interest, schizophrenia patients with positive thought disorder showed a larger attenuation of the N400 to indirectly related (versus unrelated) target words (underlined in the examples) than healthy controls. Right: When participants performed an explicit relatedness judgment task, the same patients, unlike controls, showed no attenuation of the N400 to indirectly related (versus unrelated) target words (underlined in the examples). The plots indicate one central parietal electrode site (Pz) where the N400 effect is maximal.

Figure 2

Left: Schizophrenia patients, like healthy controls, showed an increase in the N400 amplitude to critical words (underlined in the examples) that were incongruous and non-associated (versus congruous) with their preceding sentence context. Right: Schizophrenia patients, unlike healthy controls, failed to show an increase in the N400 amplitude to critical words (underlined in the examples) that were incongruous (versus congruous) with their preceding sentence context, when these words were semantically associated with the dominant meaning of a preceding homograph. The plots indicate one central parietal electrode site (Pz) where the N400 effect is maximal.

Figure 3

Left: When real-world knowledge was explicitly provided in the context, schizophrenia patients, like healthy controls, showed an attenuation of the N400 amplitude to critical words (underlined in the examples) that were congruous (versus incongruous) with their entire discourse context. Right: When the context was unconstrained, schizophrenia patients, unlike healthy controls, failed to attenuate the N400 to critical words (underlined in the examples) that were congruous (versus incongruous) with their entire discourse context. The plots indicate one central parietal electrode site (Pz) where the N400 effect is maximal.