Biomedical subjects

B Marcy

Publications and source records attributed to B Marcy.

4 recordsLinked to original sources

PubMed1993

ERP abnormalities during semantic processing in schizophrenia.

To examine the neurophysiological and cognitive characteristics of thought disturbance in schizophrenic patients, we examined the amplitude, latency, and topography of a specific event-related brain potential (ERP), the N400, which is elicited by semantically incongruent words and phrases. Twelve chronic schizophrenic patients and twelve age-matched control subjects read sentences presented visually that had either semantically correct (e.g., 'People pray in their local church') or incorrect endings (e.g., 'Every Sunday morning people pray in their local nest'). Relative to normal controls, schizophrenic patients had significantly reduced N400 amplitude and increased latency to semantically anomalous endings. Additionally, a late positive component which follows the N400 was significantly reduced in amplitude in schizophrenic patients. However, patients and controls did not differ significantly in terms of the topographical distribution of either the N400 or its late positive potential, examined at 28 electrode sites. Thus, N400 topography in schizophrenic patients was not accompanied by the asymmetry which frequently characterizes the well known auditory P300 disturbance in schizophrenic patients. We concluded that these findings may reflect a profound disturbance in attentional processes in chronic schizophrenia.

Adult↗

PubMed1990

Preservation of P300 event-related potential topographic asymmetries in schizophrenia with use of either linked-ear or nose reference sites.

Previous studies of the auditory P300 event-related potential (ERP) from our laboratory have reported a left- greater than right-sided attenuation in medicated chronic schizophrenics compared with normal controls. A possible confound in these studies has been the use of the linked-ear reference (LER), which has been criticized on the grounds that it might either induce or suppress topographic asymmetries. To test the effects of LER on P300 asymmetries in schizophrenia, we recorded ERPs with both LER and a nose reference (NR) in a group of 20 chronic medicated schizophrenics and in group of 20 age-matched normal controls. We here report: (1) confirmation of our previous P300 findings of left temporal scalp region deficit using both LER and NR with a 28-electrode montage; this feature was prominent in the wave form associated with the target stimulus, without the use of the wave form subtractions of our previous studies; (2) no statistically significant topographic differences between the LER and NR for either the schizophrenic or normal subjects; and (3) better performance of the LER in differentiating schizophrenics versus normal controls, due to lower wave form variability. We conclude that the LER is preferable for studies using subject groups and methodology similar to the present study.

Adult↗

PubMed1989

Two syndromes of schizophrenic psychopathology associated with left vs. right temporal deficits in P300 amplitude. Four case reports.

In four schizophrenic patients, we examined the relationship between clinical course, including neuroleptic response, and the following biological and psychological measures: topography of the auditory P300 event-related potential, computerized tomography (CT), Andreasen's positive and negative symptom scales, the Thought Disorder Index, and a neuropsychological test battery. Two previous studies in our laboratory had shown that schizophrenic patients were differentiated from a matched normal control group by a left temporal scalp region deficit in P300 topography. This present report compares two schizophrenic patients with the typical left temporal P300 topography deficit with two schizophrenic patients with a right temporal P300 topography deficit. The two right temporal deficit patients had more positive symptoms, more thought disorder, more severely impaired functioning, earlier age of onset, poorer response to neuroleptic medications, more diffuse cognitive deficits on a neuropsychological testing battery, and poorer premorbid history than the two left temporal deficit patients. There was some evidence for the presence of more CT abnormalities suggestive of frontal lobe pathology in the right temporal deficit patients.

Adolescent↗

PubMedDate not supplied

P300 topographic asymmetries are present in unmedicated schizophrenics.

Our laboratory has repeatedly found a left < right auditory P300 temporal lobe topographic asymmetry in right-handed, medicated schizophrenics. To determine whether this asymmetry was attributable to the effects of antipsychotic medications, we collected auditory "odd-ball" P300 event-related potentials from 14 right-handed, unmedicated schizophrenics (withdrawn from medication for an average of 21 days) and 14 right-handed, normal controls. Analysis of normalized P300 amplitudes showed a statistically significant difference in the voltage distributions between groups (a group by temporal electrode site interaction) that was consistent with a left < right temporal voltage asymmetry in schizophrenics but not in the normal controls. We conclude that P300 topographic asymmetries are present in unmedicated schizophrenics. These data are compatible with the growing body of data suggesting left temporal lobe structural abnormalities in schizophrenia.

Acoustic Stimulation↗