Auditory event-related potential abnormalities in bipolar disorder and schizophrenia
Introduction
Auditory ERPs elicited during discrimination tasks have been shown to be sensitive to schizophrenia (McCarley et al., 1997). In a typical auditory ‘oddball’ task, subjects are required to discriminate between an infrequent, target tone and a frequent, distracter tone. The frequent tone elicits the N100 and P200 components of the ERP. The target tone elicits these components, as well as the N200 and P300 components. The most robust abnormality has been reduction in amplitude of the P300 component, and less consistently, increased P300 latency (see McCarley et al., 1997, Ford, 1999, Jeon and Polich, 2003 for reviews). Abnormalities of the P300 component may be index disturbed attentional or working memory mechanisms (McCarley et al., 1997). With respect to anatomic correlates, several lines of evidence suggest that the superior temporal gyrus and adjacent inferior parietal lobe tissue are critical for the generation of the scalp recorded P300 component, including depth recordings (Halgren et al., 1995), lesion effects (Knight, 1990, O'Donnell et al., 1999), and fMRI activation (Menon et al., 1997).
Investigators have also tested the specificity of auditory ERP deficits to schizophrenia in comparison to bipolar disorder. Most studies of bipolar disorder have focused on the amplitude and latency of the P300 component. In a study of first episode patients with psychotic symptoms, Salisbury et al. (1998) found a reduction in P300 amplitude in schizophrenia, but not in affective (primarily bipolar) patients. In contrast, most studies of chronic bipolar disorder patients have found abnormal P300 responses. Some studies of chronic bipolar patients have reported amplitude reduction (Salisbury et al., 1999), others have reported latency prolongation (Souza et al., 1995, Strik et al., 1998) and Muir et al. (1991) reported both amplitude reduction and latency prolongation. While Salisbury et al., 1998, Salisbury et al., 1999 excluded patients with a history of alcohol or drug dependence (but allowed abuse), other studies have not described drug or alcohol history (Muir et al., 1991, Strik et al., 1998). In the present study, patients with a history of abuse or dependence were excluded.
The P300 component is preceded in the ERP by the N100, P200 and N200 components, which reflect earlier stages of information processing. While abnormalities of the N100, P200 and N200 components of the auditory ERP have frequently been reported in schizophrenia (O'Donnell et al., 1993, O'Donnell et al., 1994, McCarley et al., 1997, Rockstroh et al., 2001), only one of the above studies measured these early components in bipolar disorder. Muir et al. (1991) reported prolonged N200 latency in bipolar disorder, with the earlier N100 and P200 components unaffected. This suggests that bipolar patients show intact early stage processing of the auditory stimulus, but disturbed attentional or working memory mechanisms indexed by N200 and P300
The purpose of this study was to compare both early (N100, P200) and late (N200, P300) components of the auditory ERP in bipolar disorder in the manic or mixed phase of the illness, and in schizophrenia. Patients were selected who had no previous history of alcohol or substance abuse or dependence, since these disorders may contribute to P300 abnormalities.
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Participants
Thirteen Type I bipolar patients (nine females) and 12 patients with schizophrenia (four females) were recruited at the Indiana University School of Medicine Neuroscience Clinical Research Center in Indianapolis, IN. Patients were diagnosed using research modules of the Structured Clinical Interview for the DSM IV (SCID-I; First et al., 1995) in conjunction with chart review. Twenty-four control subjects (10 females) were recruited from the community via an electronic newsletter. All subjects
Behavioral performance
Response accuracy as percent correct was evaluated among groups using ANOVA. These analyses indicated that the bipolar and control groups did not differ in performance, while the schizophrenia group showed lower performance. An ANOVA with the factor diagnosis (3) revealed a significant main effect of diagnostic group on accuracy [F(2,48)=0.319, P=0.002). Mean (S.D.) values for accuracy were 99.66 (0.43) percent for the control group, 99.28 (0.87) percent for the bipolar group, and 94.78 (7.46)
Discussion
The present study examined auditory ERPs elicited in patients diagnosed with schizophrenia or bipolar disorder. Compared with control subjects, schizophrenia patients showed reduced N100, P200, and N200 amplitudes, while bipolar patients did not demonstrate these deficits. Both schizophrenia and bipolar patients had reduced P300 amplitude, and prolonged P300 latency. These results suggest that while both bipolar patients and patients with schizophrenia have reduced P300 amplitude and prolonged
Acknowledgements
This research was supported by NIMH RO3-MH63112-01 (BFO) and NIMH 1 RO1 MH62150-01 (BFO). Mr Andrew King assisted in data collection. We thank participants in the study for their time and effort.
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