It has been suggested that “willed” intentions are not correctly monitored in schizophrenia patients, that the discrepancy between will and action gives rise to positive symptoms, and that the effectiveness of dopamine receptor antagonists in reducing positive symptoms is directly linked to the induced Parkinsonism (Frith, 1987). There is growing evidence of impaired self- or performance-monitoring in schizophrenia (e.g., Ullsperger, 2006), including electrophysiologic findings of reduced error negativity (Ne; e.g., Falkenstein et al., 2000) or error-related negativity (ERN; e.g., Gehring et al., 1993), a mid-frontal negativity peaking about 100 ms after initiating an erroneous response. Several studies have reported markedly smaller ERN amplitudes in schizophrenia (e.g., Kopp and Rist, 1999; Mathalon et al., 2002; Alain et al., 2002b; Bates et al., 2002; Morris et al., 2006), with paranoid patients and those with more positive symptoms having the most prominent reductions (Kopp and Rist, 1999; Mathalon et al., 2002; Bates et al., 2002). There is some evidence that reduced ERN is modulated by clinical state in schizophrenia, because ERN amplitude increased after successful treatment with atypical antipsychotics (Bates et al., 2004).
