Objectives: Psychiatrists have long debated whether bipolar disorder (BP) and schizophrenia (SZ) are the clinical outcomes of discrete or shared causative processes. SZ shows significantly delayed peak latencies of the evoked neural oscillation (eNO) power and reduced eNO power to speech sounds in the left hemisphere in comparison to normal controls (NC), suggesting deficits in the fast mechanism for identifying speech sounds for SZ. The current study tested the hypothesis that the eNO to speech sounds could be differentiated between BP and SZ patients.Methods: The magnetoencephalographic data of 11 BP, 12 SZ, and 15 NC subjects were evaluated, and we analyzed the eNO power and phase-locking in 20-45 Hz to speech sounds and pure tones in the left hemisphere.Results: The major findings were that: (i) BP subjects exhibited larger eNO power to speech sounds compared to NC and SZ; (ii) SZ subjects showed delayed eNO and phase-locking to speech sounds specifically in the left hemisphere; and (iii) no significant differences were observed in the response to pure tones among the three groups.Conclusions: The present study showed that different patterns in eNO to speech sounds are present in BP, SZ, and NC subjects. The eNO to speech sounds in the left hemisphere is a potential index to distinguish BP and SZ.
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