Abstract
Electroencephalographic measures of information processing encompass both mid-latency evoked potentials like the pre-attentive auditory P50 potential and a host of later more cognitive components like P300 and N400.Difference waves have mostly been employed in studies of later event related potentials but here this method along with low frequency filtering is applied exploratory on auditory P50 gating data, previously analyzed in the standard format (reported in Am J Psychiatry 2003, 160:2236-8). The exploration was motivated by the observation during visual peak detection that the AEP waveform was different in the patient group, although this was not reflected by the peak measures. The sample included un-medicated schizophrenia spectrum patients (n = 17) and healthy controls (n = 24). The patients had an attenuated difference P50. This attenuation was primarily seen in the sub-sample of patients with severe negative symptoms. The difference attenuation was due to low amplitude at the first stimulus. This suggests an abnormality in readiness more than an abnormality in gating in the patient group.
Highlights
The deficiency in auditory P50 gating reported in numerous studies of schizophrenic patients has been one of the experimental findings that have supported the theory of defect sensory gating in schizophrenia [1]
While P50 gating mostly has been reported as a ratio measure (S2/S1 or 1- S2/S1 × 100), it has been suggested that a difference measure might be more reliable [2]
The patients had a negative difference amplitude in the 30–70 ms latency range frontally, while the healthy controls had a positive P50 difference component, a finding that is in agreement with most previous studies of P50 gating in schizophrenia based on 10–50 Hz filtered data and the ratio measure [7,13]
Summary
The deficiency in auditory P50 gating reported in numerous studies of schizophrenic patients has been one of the experimental findings that have supported the theory of defect sensory gating in schizophrenia [1]. P50 gating is the relative amplitude reduction of auditory evoked potential (AEP) P50 from the first stimulus (S1) to the second stimulus (S2). The latter report suggested the use of the traditional peak amplitudes for the difference measures. Extending this idea to the whole waveform, subtraction waveforms called difference waves are investigated presently. The MMN is a negative potential shift evoked when a deviant stimulus is presented in a series of wellknown stimuli. It is observed even when attention is (page number not for citation purposes)
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