A comparative study on long-term evoked auditory and visual potential responses between Schizophrenic patients and normal subjects

Abstract

Background: The electrical signals measuring method is recommended to examine the relationship between neuronal activities and measure with the event related potentials (ERPs) during an auditory and a visual oddball paradigm between schizophrenic patients and normal subjects. The aim of this study is to discriminate the activation changes of different stimulations evoked by auditory and visual ERPs between schizophrenic patients and normal subjects.

Methods: Forty-three schizophrenic patients were selected as experimental group patients, and 40 healthy subjects with no medical history of any kind of psychiatric diseases, neurological diseases, or drug abuse, were recruited as a control group. Auditory and visual ERPs were studied with an oddball paradigm. All the data were analyzed by SPSS statistical software version 10.0.

Results: In the comparative study of auditory and visual ERPs between the schizophrenic and healthy patients, P300 amplitude at Fz, Cz, and Pz and N100, N200, and P200 latencies at Fz, Cz, and Pz were shown significantly different. The cognitive processing reflected by the auditory and the visual P300 latency to rare target stimuli was probably an indicator of the cognitive function in schizophrenic patients.

Conclusions: This study shows the methodology of application of auditory and visual oddball paradigm identifies task-relevant sources of activity and allows separation of regions that have different response properties. Our study indicates that there may be slowness of automatic cognitive processing and controlled cognitive processing of visual ERPs compared to auditory ERPs in schizophrenic patients. The activation changes of visual evoked potentials are more regionally specific than auditory evoked potentials.

Figure 1

Signal processing of evoked potential responses in control and schizophrenic groups.(a) The EEG signals of behavioral performance at a task in which subjects had to identify and temporally order rapidly successive brief stimuli that in some trials. (b) Examples of evoked potential responses recorded in The Brain Atlas III Computer of the Biologic System Company. The system's versatility allows the user to record up to 4 sets of stimulus-evoked activity (including auditory ERP, visual ERP etc) and display and analyze the data in a variety of ways. The amplifier was used as follows: high filter, 30; low filter; 1.0; and gain, 20,000. (c)&(d) Averages were computed for the brain responses to target tones. Peak P300 amplitude, which accounts for individual variations in P300 latency, was measured as the most positive point from 250 to 400. Peak P400 amplitude, which accounts for individual variations in P400 latency, was measured as the most positive point from 400 to 500. The components of ERPs were identified as follows, P100, N100, P200, N200, P300, and P400. The figure 1c showed the averaged signals of evoked potentials from one normal control. The figure 1d showed the averaged signals of evoked potentials from one schizophrenic patient.

Figure 2

The activation changes from latency and amplitude differences at all the scalp channels were summarized between auditory and visual event-related potentials in control and schizophrenic groups. This difference remained significant (p < 0.01) for 43 schizophrenic patients and 40 control subjects after the subject-mean ERP was subtracted from each trial. The average ERP of the auditory and visual stimulus and the peaks conventionally termed N100, N200, P200 and P300. The scalp map indicates that it was obvious that the visual ERP is more specific to identify schizophrenic patients than the auditory ERP over the Fz, Cz and Pz regions.