Schizophrenia patients have abnormal neural responses to increasing stimulus density in auditory cortex
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Electro-/magneto-encephalography studies indicate that schizophrenia subjects have decreased amplitudes of transient (N100/M100) and entrained (steady-state) neural responses to auditory stimuli. The current study extends this research by (i) focusing analyses on auditory cortices, (ii) assessing a wide range of stimulation frequencies with long driving periods, and (iii) evaluating the relationships between transient and sustained auditory responses between hemispheres. Seventeen schizophrenia (SZ) and 17 healthy (H) individuals participated. Stimuli were 1500ms binaural broadband noise sequences modulated at 5-, 20-, 40-, 80- or 160-Hz. While auditory cortical transient responses for H increased linearly with stimulus density, this effect was weaker or absent in SZ. SZ also had a right lateralized deficit in evoked entrainment to 40-Hz stimuli and a bilateral deficit at 5-Hz and 80-Hz. Overall, there was an altered relationship between increasing stimulus density and evoked auditory cortical responses among SZ which may underlie their commonly reported abnormalities in auditory processing.