Aberrant auditory processing in schizophrenia and in subjects at ultra-high-risk for psychosis.

The N1 and the mismatch negativity (MMN) responses observed in electroencephalographic and magnetoencephalographic (MEG) recordings reflect sensory processing, sensory memory, and adaptation and are usually abnormal in patients with schizophrenia. However, their differential sensitivity to ultra-high-risk (UHR) status is controversial. The current study evaluated the sensitivity of MEG N1m, N1m adaptation, and magnetic counterpart of MMN (MMNm) in 16 UHR subjects, 15 schizophrenia patients, and 18 healthy controls (HCs) during a passive auditory oddball task. N1m adaptation was assessed using the difference in N1m dipole moment between the first and last standard tones in a standard stimulus sequence. N1m adaptation occurred in HCs, whereas neither the UHR nor the schizophrenia groups showed adaptation to the standard tone on repeated presentations. The UHR group had values between those for HCs and schizophrenia patients. Additionally, MMNm dipole moment was reduced in both the UHR and patient groups compared with HCs, whereas the UHR and schizophrenia groups did not differ from each other. These findings indicated that both N1m adaptation and MMNm were altered in UHR subjects and in schizophrenia patients, despite unaffected N1m dipole moment to the first standard tones. Moreover, both UHR and schizophrenia groups failed to show adaptation of the N1m to repeated standard tones. This failure in adaptation was more severe in patients than UHR subjects, suggesting that auditory adaptation may be sensitive to the progression of the illness and be an early biomarker of UHR for psychosis. Deficits in auditory sensory memory, on the other hand, may be similarly impaired in both groups.