There is growing evidence that impaired sensory-processing significantly contributes to the cognitive deficits found in schizophrenia. For example, the mismatch negativity (MMN) and P3a event-related potentials (ERPs), neurophysiological indices of sensory and cognitive function, are reduced in schizophrenia patients and may be used as biomarkers of the disease. In agreement with glutamatergic theories of schizophrenia, NMDA antagonists, such as ketamine, elicit many symptoms of schizophrenia when administered to normal subjects, including reductions in the MMN and the P3a. We sought to develop a nonhuman primate (NHP) model of schizophrenia based on NMDA-receptor blockade using subanesthetic administration of ketamine. This provided neurophysiological measures of sensory and cognitive function that were directly comparable to those recorded from humans. We first developed methods that allowed recording of ERPs from humans and rhesus macaques and found homologous MMN and P3a ERPs during an auditory oddball paradigm. We then investigated the effect of ketamine on these ERPs in macaques. As found in humans with schizophrenia, as well as in normal subjects given ketamine, we observed a significant decrease in amplitude of both ERPs. Our findings suggest the potential of a pharmacologically induced model of schizophrenia in NHPs that can pave the way for EEG-guided investigations into cellular mechanisms and therapies. Furthermore, given the established link between these ERPs, the glutamatergic system, and deficits in other neuropsychiatric disorders, our model can be used to investigate a wide range of pathologies.brain | psychiatry | neurology | monkey | medicine S chizophrenia is a multifaceted disorder that may originate from neuronal pathology in multiple brain systems (1). Current theories suggest that some of the sensory and cognitive symptoms of schizophrenia may, at least partially, result from dysfunction of the glutamate neurotransmitter system (2). In support of this theory, it has been found that acute subanesthetic doses of the N-methyl-D-aspartate receptor (NMDAR) antagonist ketamine induces sensory and cognitive deficits akin to those experienced by schizophrenia patients, as well as decreases of the mismatch negativity (MMN) and P3 event-related potential (ERP) amplitudes (3).The MMN is thought to reflect preattentive detection of a deviant stimulus (4), whereas the P3 is thought to reflect the redirection of attention to that deviant stimulus (5). In an oddball paradigm, responses to deviant (or "oddball") stimuli occurring among a sequence of standard stimuli are measured. The MMN is obtained by subtracting the ERP to the standard stimulus from the ERP to the deviant stimulus, whereas the P3a is typically observed in the ERP to deviants.Schizophrenia patients appear less able to detect and direct attention to novel stimuli than healthy controls (6). Consistent with this behavioral deficit, the amplitudes of both the MMN (7) and the P3 (8) have been found to be reduced in schizophrenia patients, l...