Cortical Volume and 40-Hz Auditory-Steady-State Responses in Patients with Schizophrenia and Healthy Controls

Abstract

Background:Abnormalities in the 40-Hz auditory steady-state response (ASSR) of the gamma range have beenreported in schizophrenia (SZ) and are regarded as important pathophysiological features. Many of the previousstudies reported diminished gamma oscillations in SZ, although some studies reported increased spontaneousgamma oscillations. Furthermore, brain morphological correlates of the gamma band ASSR deficits have rarelyexamined. We investigated different measures of the 40-Hz ASSR and their association with brain volumes andpsychological measures of SZ.Methods:The 40-Hz ASSR was measured for 80 dB click sounds (1 ms, 500-ms trains at 40-Hz, with 3050 to 3500inter-train interval) using electroencephalography with 64 electrodes in 33 patients with SZ (male: 16, female:17 (age range: 21–60)) and 30 healthy controls (HCs) (male: 13, female: 17 (age range: 23–64)). Four gammaoscillation measures (evoked power, spontaneous oscillations (baseline and total power), and inter-trial phasecoherence (ITC)) were assessed. The source activities of the ASSR were also analyzed. Brain volumes wereassessed using high-resolution magnetic resonance imaging and voxel-based morphometry and superior tem-poral gyrus (STG) volume measures were obtained.Results:Patients with SZ had larger total and evoked powers and higher ITC than HCs. Both groups showedsignificantly different association between mean evoked power and right STG volume. In HCs but not SZ, meanevoked power showed significant positive correlation with right STG volume. In addition, the two groupsshowed significantly different association between verbalfluency and mean evoked power. High evoked powerwas significantly correlated with poor verbalfluency in SZ.Conclusions:The current study found increased gamma oscillation in SZ and suggests significant involvement ofthe STG in gamma oscillations.