Modulation of spectral power and phase coherence of infrequent auditory pitch detection in schizophrenia and subjects at ultra high-risk for psychosis

Abstract

Introduction: Findings of abnormal brain response during an auditory discrimination task provide crucial neurophysiological evidence in patients with mental illnesses. Previous research has repeatedly reported that sensory memory abnormalities in audition may be a core feature of mental disorders such as schizophrenia. Nevertheless, major neurophysiological findings have shown superimposed brain activity disregarding zthe disparate functions of each frequency band. In recent years, some studies have established the importance of lower frequencies in auditory pitch detection, but the mechanisms are still equivocal. In this paper, we will investigate altered lower frequency activation in patients with schizophrenia and individuals at ultra high-risk (UHR). Methods: This study was performed using a passive auditory oddball task in 36 individuals at UHR for psychosis, 37 schizophrenia patients and 38 healthy controls. Whole-head magnetoencephalography (MEG) was conducted in a shielded room while subjects were asked to play a computer game while listening to a stream of auditory stimuli. The auditory paradigm consisted of frequent standard tones (50 ms duration, 81.2 %) and infrequent deviant tones (100 ms duration, 18.8%). Oscillatory responses to each stimulus were examined by employing the Morlet wavelet-based transformation, using measures of both spectral power and inter-trial coherence. We compared the results of lower frequency bands in temporal regions for each group. Results: Theta and alpha activations showed different results in each group. In theta band (4-7 Hz), only patients with schizophrenia revealed reduced power and ITC in temporal regions for given infrequent stimuli. Even though the theta response in UHR subjects was not significantly different compared to that of HCs, alpha band (8-12 Hz) phase coherence in the right hemisphere was altered. Conclusions: Our current results indicate that schizophrenia and UHR groups presented with aberrant low frequency oscillatory phenomena during an involuntary auditory attention task. While inadequate theta activity reflects neurobiological breakdown in full-blown psychosis, abnormal alpha oscillations may occur in prodromal state. The study allows a deeper understanding of the neural dynamics underlying altered low frequency oscillations in schizophrenia. It suggests that impairment of the auditory capturing process is affected by separate frequency oscillations in each psychotic state. Additionally, altered phase coherence may serve as an indicative trait for UHR individuals.