P300 event-related potential in late-onset schizophrenia.

P300 event-related potential in late-onset schizophrenia The P300 event-related potential (ERP) is a late positive waveform that is typically maximal at centroparietal midline sites 300 msec post-stimulus in simple categorization tasks. Reduction in auditory P300 amplitude has been widely reported in young schizophrenic patients. The degree of amplitude reduction has been related to the degree of psychopathology, and seems relatively insensitive to changes in clinical status or to drug treatment. Auditory latency changes have not been so consistent, with some studies finding increased latencies but others not (Ford et al., 1994). Visual P300s appear to be more sensitive to changes in the clinical state of schizophrenic patients and are thus more variable than auditory P300 event-related potentials. Nearly all ERP studies of schizophrenia have been conducted on persons who had a typical onset of the disorder in young adulthood. For several years there has been increasing interest in late-onset schizophrenia (defined as illness-onset between the ages of 40 and 60) (Howard et al., 2000). We were able to find only one ERP study investigating schizophrenia with onset of illness after age 40. In that study (Olichney et al., 1998), 14 patients with late-onset schizophrenia did not have significantly smaller P300 auditory amplitudes than subjects from a normal control group, but patients with early-onset schizophrenia did. The purpose of this investigation was to further assess auditory and visual P300 ERPs in patients with late-onset schizophenia. Subjects were selected from hospitalized patients who met DSM-IV criteria (American Psychiatric Association, 1994) for schizophrenia whose symptoms had begun after age 40 but before age 60. Diagnoses were determined by a boardcertified psychiatrist. Symptoms had been present in each patient for 2 years or less at the time of the study, and in each case this was their first hospitalization. They had either never been treated with antipsychotic medication prior to admission, or if they had in the past, were not compliant and were off medication the month prior to admission. Each patient underwent history and physical examination and laboratory assessment, including complete blood count, chemistry survey, liver function studies, thyroid-stimulating hormone, urinalysis, and testing for syphilis. Potential subjects were excluded from the study if they had a medical illness or were on medications that could affect EEG, psychiatric illness other than schizophrenia, or significant histories of drug or alcohol abuse. Signed informed consent was obtained from each subject. Prior to completion of the study, the only medication given was haloperidol, on an as-needed basis. Each subject underwent magnetic resonance imaging