Schizophrenia has been conceptualized by dysfunctional cognition and behavior related to abnormalities in neural circuitry. The functioning of the neural circuitry can be assessed using the auditory steady state response (ASSR). Moreover, in recent years, research on high (>60 Hz) gamma band oscillations has become of increasing interest. The current study used whole-head, 306-channel magnetoencephalography (MEG) and investigated low and high gamma band oscillations with the ASSR. The subjects comprised 17 patients with schizophrenia and 22 controls. The current study investigated the MEG-ASSR elicited by click trains of 20-, 30-, 40- and 80-Hz frequencies, and symptom-ASSR associations in patients with schizophrenia. The mean power, phase-locking factor, dipole moments and source locations of the ASSR were estimated. The main findings were: (1) patients with schizophrenia showed bilaterally reduced ASSR power and dipole moments specific to the 40-Hz and 80-Hz frequencies; (2) patients with schizophrenia showed less right-greater-than-left 40-Hz ASSR power and phase-locking factor compared with healthy subjects, indicating that schizophrenics may be characterized by an abnormal asymmetry of the 40-Hz ASSR; (3) increased severity of global hallucinatory experiences was significantly associated with smaller left 80-Hz MEG-ASSR in patients with schizophrenia. The current study highlights the high and low frequency gamma abnormalities and provides clear evidence that schizophrenia is characterized by abnormalities in neural circuitry.
Periodic auditory click stimulation has been reported to elicit an auditory steady state response (ASSR). The ASSR has been suggested to reflect the efficiency of γ-amino butyric acid (GABA) inhibitory interneuronal activity. Although a potential role for GABAergic dysfunction has been previously proposed, the role of neural synchronization in the ASSR in people with bipolar disorder (BD) has received little attention. In the current study, we investigated ASSRs to 20 Hz, 30 Hz, 40 Hz and 80 Hz click trains in BD patients. A total of 14 (4 males) BD patients and 25 (10 males) healthy controls participated in this study. ASSRs were obtained using whole-head 306-channel magnetoencephalography to calculate, ASSR power values and phase locking factors (PLF). BD patients exhibited significantly reduced mean ASSR power and PLF values bilaterally at frequencies of 30, 40, and 80 Hz (p<0.05 for these frequencies). At 20 Hz, bipolar patients showed no significant reduction in mean ASSR power and PLF values. There was a significant negative correlation between 80 Hz-ASSR-power values obtained from the right hemisphere and scores on the Hamilton Depression Rating Scale (rho = −0.86, p = 0.0003). The current study showed reduced low and high gamma band ASSR power and PLF bilaterally with no significant beta band ASSR reduction in BD patients. BD patients are characterized by deficits in gamma band oscillations, which may be associated with GABA inhibitory interneuronal activity dysfunction.
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