<h3>Background</h3> In patients with schizophrenia, deficient generation of mismatch negativity (MMN)—an event-related potential (ERP) indexing auditory sensory ("echoic") memory—and a selective increase of "context dependent" ("BX") errors in the "A-X" version of the Continuous Performance Test (AX-CPT) indicate an impaired ability to form and use transient memory traces. Animal and human studies implicate deficient<i>N</i>-methyl-D-aspartate receptor (NMDAR) functioning in such abnormalities. In this study, effects of the NMDAR antagonists ketamine on MMN generation and AX-CPT performance were investigated in healthy volunteers to test the hypothesis that NMDARs are critically involved in human MMN generation, and to assess the nature of ketamine-induced deficits in AX-CPT performance. <h3>Methods</h3> In a single-blind placebo-controlled study, 20 healthy volunteers underwent an infusion with subanesthetic doses of ketamine. The MMN-to-pitch and MMN-to-duration deviants were obtained while subjects performed an AX-CPT. <h3>Results</h3> Ketamine significantly decreased the peak amplitudes of the MMN-to-pitch and MMN-to-duration deviants by 27% and 21%, respectively. It induced performance deficits in the AX-CPT characterized by decreased hit rates and specific increases of errors (BX errors), reflecting a failure to form and use transient memory traces of task relevant information. <h3>Conclusions</h3> The NMDARs are critically involved in human MMN generation. Deficient MMN in schizophrenia thus suggests deficits in NMDAR-related neurotransmission.<i>N</i>-methyl-D-aspartate receptor dysfunction may also contribute to the impairment of patients with schizophrenia in forming and using transient memory traces in more complex tasks, such as the AX-CPT. Thus, NMDAR-related dysfunction may underlie deficits in transient memory at different levels of information processing in schizophrenia.

Ketamine-Induced Deficits in Auditory and Visual Context-Dependent Processing in Healthy Volunteers