Brain potentials and cognitive dysfunction in schizophrenia.

Abstract

Schizophrenia, a disorder characterized by attentional and cognitive disturbances, has been investigated using evoked-brain responses. Little work, however, has been done to investigate event-related potentials (ERPs) and cognitive dysfunction in schizophrenia. This lack stands in contrast to the literature on ERPs and cognition in normals, where in the emerging cognitive psychophysiology field, ERPs are considered markers of specific information processing, and include: (1) N100 (stimulus feature encoding); (2) P300 (cognitive updating); and (3) N400 (semantic incongruity). Since one of the current directions in schizophrenia research is to study electrophysiological changes and cognitive dysfunction, the three studies in this thesis were based on a newly-developed cognitive psychophysiological paradigm. The first study's aim was to see whether, when compared to normals, schizophrenics would show P300 reductions to visual-semantic "oddball" stimuli. The second study was based on the abstract-concrete view of schizophrenia, which posits that abstract thinking in schizophrenia is impaired and results in a reliance on concrete thinking; the aim was to see whether schizophrenics would show behavioral and ERP correlates of slips to concrete thinking. The third study's aim was to see whether schizophrenics would show N400 differences to incongruous/congruous categories. Nine normals were MMPI/SADS assessed; six schizophrenics were RDC/DSM-III-R diagnosed. Based on Harrow and Quinlan's Bizarre-Idiosyncratic Index, schizophrenics showed definite thought disorder in contrast to normals who showed no thought disorder. ERPs were recorded from Pz, Cz, and Fz electrodes (referenced to linked mastoids). Results emerged in the predicted directions. When compared to normals, schizophrenics showed: (1) P300 reductions to visual-semantic "oddball" stimuli; (2) behavioral correlates of slippage to concrete thinking; (3) an N100 increase to abstract/concrete categories, and (4) N400 reductions to incongruous category stimuli. While schizophrenics showed predicted effects for P300, N400, and behavioral slips to concrete thinking, the N100 increase in response to the abstract/concrete categories was unexpected. These findings suggest that, as processing becomes more complex, schizophrenics show later deficits. These data also demonstrate that the use of a cognitive psychophysiological paradigm to study ERPs and cognitive dysfunction in schizophrenia is viable, justified, and warrants further investigation.