Aberrant auditory evoked responses in schizophrenia: Evidence from single-trial analysis

Abstract

The average N100 (a negative response occurring around 100 ms poststimulus) component of the auditory evoked potential (EP) has been recently used in the study of schizophrenia. Averaging, however, eliminates all temporal variability of the recorded signals and, therefore, hampers the exploration of the temporal dynamics underlying the generation of the N100 component. In this study, we analyzed EPs on a single-trial basis using an iterative independent component analysis procedure that is capable of extracting individual components out of an entire EP waveform. This approach allowed estimation of an N100 in each single trial and measurement of its morphological features such as polarity, which could be either negative (most frequently) or positive (less frequently). In the latter case, the N100 component was termed aberrant. We analyzed responses from 23 normal controls (NC) and 15 schizophrenia (SZ) patients in a paired stimulus paradigm, where a first stimulus S(1) was followed by a second one S(2) 0.5 s later. To compare N100 responses within and across the two subject groups, we defined a negative polarity index NPI as the percentage of single trials that had a negative polarity N100. Our results show significantly higher NPI values in NC compared to SZ, for both the S(1) and S(2) responses. Additionally, the difference in NPI values between the S(1) and S(2) responses was significant in NC but not in SZ. We conclude that both normal and schizophrenia subjects exhibit aberrant N100 responses, but these events are more frequent in the SZ patient group. The higher number of aberrant responses can explain the lower amplitude EPs typically observed in schizophrenia, and may be one of the factors contributing to sensory gating deficits consistently reported in these patients.

Differential sensory fMRI signatures in autism and schizophrenia: Analysis of amplitude and trial-to-trial variability

“…Greater variability has been reported in the amplitude and latency of P1 ERP responses to visual stimuli (Milne, 2011). There are similar reports in schizophrenia (Jordanov et al, 2011; Müller et al, 1986), which could potentially contribute to smaller average responses (Iyer, Boutros & Zouridakis, 2011). Greater trial-to-trial variability may be the result of an imbalance between neural excitation and inhibition, which is associated with autism (Jamain et al, 2002; Markram, Rinaldi & Masrkram, 2007; Vattikuti & Chow, 2010; Rubenstein & Merzenich, 2003; Sigurdsson, in press; Uhlhaas, 2013; Lisman, 2012), and with schizophrenia (Baron-Cohen et al, 2009; Gomot et al, 2002; Simmons et al, 2009).…”

Schizophrenia Assessment Using Single-Trial Analysis of Brain Activity

“…Moreover, when compared with time-frequency wavelet denoising, iICA performed equally well or better over a wide range of experimental conditions and SNRs [47]. The iICA method has been used to analyze EP activity with data obtained at different labs and under different experimental protocols, including a simple N100 auditory task and typical paired stimulus P50 and N100 paradigms [48,49]. The following sections describe the various steps of the iICA method along with application examples on data recorded from normal control subjects and schizophrenia patients.…”