In a recent study, researchers found that gamma-band induced power during auditory steady-state response testing most accurately distinguished patients with schizophrenia from neurotypical controls. This measure was found alongside other abnormalities including reduced 40 Hz phase-locking factor, elevated low-frequency power, and reduced alpha-band rest–task shifts.
Led by Ryo Mitoma, MD, of the Department of Neuropsychiatry, Graduate School of Medical Sciences at Kyushu University in Fukuoka, Japan, the researchers reported findings on abnormalities in spontaneous and task-evoked neural oscillations, as well as altered rest–task modulation, in patients with schizophrenia (SZ). Results demonstrated significantly reduced 40 Hz phase-locking factor (PLF) in SZ compared with neurotypical controls (NC; mean = 0.252 vs 0.330) over the left parieto-occipital region. No significant group differences in evoked power or phase-locking angle were found. Induced and resting power in the low-frequency range (4 to 10 Hz) were elevated across widespread scalp regions in SZ. In the gamma range (39 to 100 Hz), induced power was significantly higher in SZ within a right-hemisphere cluster during the auditory steady-state responses (ASSR) state (mean = −25.917 vs −26.441 in NC).
The largest effect size for group discrimination was observed for gamma-band induced power (Cohen d = 0.745), followed by PLF (d = 0.703). Rest–task shift analysis revealed a group-by-state interaction in the theta-beta range (5 to 23 Hz), primarily in the alpha band (8 to 13 Hz). NC exhibited a marked reduction in induced vs resting power, whereas SZ did not. Induced power in this cluster was higher in SZ than NC during the task state. No significant correlations were found between electroencephalography (EEG) measures and symptom severity or antipsychotic dose.
The researchers examined 68 SZ patients (mean age= 34.9 years; 35 men) and 66 NC (mean age= 37 years; 30 men) using EEG to assess 40 Hz ASSRs and resting-state activity. Participants underwent a resting EEG recording followed by presentation of 150 trains of 40 Hz clicks. Stimulus-evoked measures included PLF, evoked power, and phase-locking angle. Spontaneous activity was quantified as induced power during ASSR and resting power across frequencies from 4 to 100 Hz. Rest–task shift was defined as the difference between induced and resting power in identical frequency bins. Statistical analyses used cluster-based permutation t tests, repeated-measures ANOVA, and effect size comparisons.
The researchers were not able to evaluate oscillatory activity independently of the potential effects of antipsychotics because patients with SZ were treated with several different antipsychotic medications. They also could not rule out possible pharmacological effects on their results. They suggested that future studies should examine a larger number of EEG indices and features to better understand the underlying neural mechanisms of the highly heterogeneous pathology of SZ.
Yoji Hirano, MD, PhD, is an Associate Editor and Art Advisor of Psychiatry and Clinical Neurosciences and was excluded from all editorial decision-making for this article; the authors report no other commercial or financial conflicts of interest.