Abstract
BackgroundOscillatory electroencephalogram (EEG) abnormalities may reflect neural circuit dysfunction in neuropsychiatric disorders. Previously we have found positive correlations between the phase synchronization of beta and gamma oscillations and hallucination symptoms in schizophrenia patients. These findings suggest that the propensity for hallucinations is associated with an increased tendency for neural circuits in sensory cortex to enter states of oscillatory synchrony. Here we tested this hypothesis by examining whether the 40 Hz auditory steady-state response (ASSR) generated in the left primary auditory cortex is positively correlated with auditory hallucination symptoms in schizophrenia. We also examined whether the 40 Hz ASSR deficit in schizophrenia was associated with cross-frequency interactions.Sixteen healthy control subjects (HC) and 18 chronic schizophrenia patients (SZ) listened to 40 Hz binaural click trains. The EEG was recorded from 60 electrodes and average-referenced offline. A 5-dipole model was fit from the HC grand average ASSR, with 2 pairs of superior temporal dipoles and a deep midline dipole. Time-frequency decomposition was performed on the scalp EEG and source data.ResultsPhase locking factor (PLF) and evoked power were reduced in SZ at fronto-central electrodes, replicating prior findings. PLF was reduced in SZ for non-homologous right and left hemisphere sources. Left hemisphere source PLF in SZ was positively correlated with auditory hallucination symptoms, and was modulated by delta phase. Furthermore, the correlations between source evoked power and PLF found in HC was reduced in SZ for the LH sources.ConclusionThese findings suggest that differential neural circuit abnormalities may be present in the left and right auditory cortices in schizophrenia. In addition, they provide further support for the hypothesis that hallucinations are related to cortical hyperexcitability, which is manifested by an increased propensity for high-frequency synchronization in modality-specific cortical areas.
Highlights
Oscillatory electroencephalogram (EEG) abnormalities may reflect neural circuit dysfunction in neuropsychiatric disorders
Since the cortical generators of the auditory steady-state response (ASSR) are located in the primary auditory cortex (e.g., [9,10]), and the visual β oscillation was observed over occipital cortex, oscillations demonstrating positive correlations between phase synchronization and hallucination symptoms may originate in sensory cortical areas associated with the modality of the hallucinations
Source localization Most studies in which source localization of the ASSR is performed have utilized magnetoencephalography (MEG), which is primarily sensitive to sources that are tangential to the scalp surface [28]
Summary
Oscillatory electroencephalogram (EEG) abnormalities may reflect neural circuit dysfunction in neuropsychiatric disorders. We have found positive correlations between the phase synchronization of beta and gamma oscillations and hallucination symptoms in schizophrenia patients These findings suggest that the propensity for hallucinations is associated with an increased tendency for neural circuits in sensory cortex to enter states of oscillatory synchrony. Since the cortical generators of the ASSR are located in the primary auditory cortex (e.g., [9,10]), and the visual β oscillation was observed over occipital cortex, oscillations demonstrating positive correlations between phase synchronization and hallucination symptoms may originate in sensory cortical areas associated with the modality of the hallucinations Consistent with this hypothesis, Baldeweg and colleagues reported that a psychiatric patient experiencing somatic hallucinations evinced γ oscillations over sensorimotor cortex [11], and Ropohl et al [12] found abnormally large β oscillations localized to the left auditory cortex in a schizophrenia patient with treatment-resistant auditory hallucinations
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