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The N400 event-related brain potential (ERP), a negative voltage deflection occurring approximately 400ms after onset of any meaningful stimulus, is reduced in amplitude when the stimulus is preceded by related context. Previous work has found this N400 semantic priming effect to be decreased in schizophrenia, suggesting impairment in using meaningful context to activate related concepts in semantic memory. Thus, N400 amplitude may be a useful biomarker of abnormal semantic processing and its response to treatment in schizophrenia. To help assess the validity of N400 amplitude as a longitudinal measure in schizophrenia, we evaluated its test-retest reliability. ERPs were recorded in sixteen schizophrenia patients who viewed prime words, each followed at 300- or 750-ms stimulus-onset asynchrony (SOA) by a target that was either a related or unrelated word, or nonword. Participants' task was to indicate whether or not the target was a real word. They were retested on the same procedure one week later. Test-retest reliability was assessed by calculating Pearson's r and intraclass correlation coefficients (ICCs) across timepoints for N400 amplitudes for related and unrelated targets, at each SOA. Consistent with previous results, there were no significant differences between patients' N400 amplitudes for related and unrelated targets, at any SOA/timepoint combination. Pearson's r and ICCs for N400 amplitudes at Fz across timepoints were significant for both target types at each SOA (ranges: r 0.52-0.64, ICC 0.52-0.63; all p

Impaired illness insight in schizophrenia is associated with non-adherence and worse outcomes. Schizophrenia patients also exhibit error-monitoring deficits, which have been proposed to cause poor insight. To test this hypothesis, we examined whether schizophrenia patients' deficits in neurophysiological error-monitoring indices, the error-related negativity (ERN) and error positivity (Pe) event-related potential (ERP) amplitudes, are associated with impaired insight. ERPs were recorded in 18 schizophrenia patients and 18 normal comparison participants during a Stroop task. Patients' subnormal ERN and Pe amplitudes did not correlate with insight, suggesting that impaired insight in schizophrenia stems from neurocognitive mechanisms other than deficient error monitoring. Canadian Institutes of Health Research (INO-112359)

Elicited by any meaningful stimulus, the N400 event-related potential (ERP) component is reduced when the stimulus is related to a preceding one. This N400 semantic priming effect has been used to probe abnormal semantic relationship processing in clinical disorders, and suggested as a possible biomarker for treatment studies. Validating N400 semantic priming effects as a clinical biomarker requires characterizing their test-retest reliability.We assessed test-retest reliability of N400 semantic priming in 16 healthy adults who viewed the same related and unrelated prime-target word pairs in two sessions one week apart.As expected, N400 amplitudes were smaller for related versus unrelated targets across sessions. N400 priming effects (amplitude differences between unrelated and related targets) were highly correlated across sessions (r=0.85, P0.0001), but smaller in the second session due to larger N400s to related targets.N400 priming effects have high reliability over a one-week interval. They may decrease with repeat testing, possibly because of motivational changes.Use of N400 priming effects in treatment studies should account for possible magnitude decreases with repeat testing. Further research is needed to delineate N400 priming effects' test-retest reliability and stability in different age and clinical groups, and with different stimulus types.