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• Interhemispheric signal propagation was elevated in schizophrenia and depression patients relative to healthy controls. • Interhemispheric signal propagation did not differ between patient groups. • There were no medication effects on interhemispheric signaling from inter-individual comparisons and no significant correlation with symptom severity. Altered interhemispheric connectivity is implicated in the pathophysiology of schizophrenia (SCZ) and major depressive disorder (MDD) and may account for deficits in lateralized cognitive processes. We measured transcranial magnetic stimulation evoked interhemispheric signal propagation (ISP), a non-invasive measure of transcallosal connectivity, and hypothesized that the SCZ and MDD groups will have increased ISP compared to healthy controls. We evaluated ISP over the dorsolateral prefrontal cortex in 34 patients with SCZ and 34 patients with MDD compared to 32 age and sex-matched healthy controls. ISP was significantly increased in patients with SCZ and patients with MDD compared to healthy controls but did not differ between patient groups. There were no effects of antidepressant, antipsychotic, and benzodiazepine medications on ISP and our results remained unchanged after re-analysis with a region of interest method. Altered ISP was found in both SCZ and MDD patient groups. This indicates that disruptions of interhemispheric signaling processes can be indexed with ISP across psychiatric populations. These findings enhance our knowledge of the physiological mechanisms of interhemispheric imbalances in SCZ and MDD, which may serve as potential treatment targets in future patients. [ABSTRACT FROM AUTHOR]

Background: Working memory deficits represent a core feature of schizophrenia. These deficits have been associated with dysfunctional dorsolateral prefrontal cortex (DLPFC) cortical oscillations. Theta-gamma coupling describes the modulation of gamma oscillations by theta phasic activity that has been directly associated with the ordering of information during working memory performance. Evaluating theta-gamma coupling may provide greater insight into the neural mechanisms mediating working memory deficits in this disorder.Methods: Thirty-eight patients diagnosed with schizophrenia or schizoaffective disorder and 38 healthy controls performed the verbal N-Back task administered at 4 levels, while EEG was recorded. Theta (4-7Hz)-gamma (30-50Hz) coupling was calculated for target and non-target correct trials for each working memory load. The relationship between theta-gamma coupling and accuracy was determined.Results: Theta-gamma coupling was significantly and selectively impaired during correct responses to target letters among schizophrenia patients compared to healthy controls. A significant and positive relationship was found between theta-gamma coupling and 3-Back accuracy in controls, while this relationship was not observed in patients.Conclusions: These findings suggest that impaired theta-gamma coupling contribute to working memory dysfunction in schizophrenia. Future work is needed to evaluate the predictive utility of theta-gamma coupling as a neurophysiological marker for functional outcomes in this disorder. [ABSTRACT FROM AUTHOR]

Abstract: Brain oscillations are increasingly used for understanding complex psychiatric disorders. Gamma (30–50Hz) oscillations have warranted special attention due to their omnipresence in cognitive tasks. For patients with schizophrenia (SCZ), a disease associated with poor cognition, abnormal gamma oscillations have been reported in many experimental paradigms. The goal of this paper is to review the literature on gamma oscillations in SCZ. The review is structured into four sections. First, the functional role, neurobiology, and analysis of brain oscillations, especially gamma oscillations will be outlined. Second, the neurobiological abnormalities of SCZ in relation to gamma oscillations will be reviewed. Third, selected paradigms for investigating irregular gamma oscillations in SCZ will be discussed in detail. Finally, a discussion on the limitations of current findings and potential future research directions will be provided. The reviewed evidence suggests that gamma oscillations are disrupted in SCZ and could account for cognitive disturbances in this disorder. With additional analysis and experimentation, these indices may ultimately serve as endophenotypes that facilitate the development of etiologically based diagnostic methods, foster early identification and treatment, and advance our understanding of the complex genetic mechanisms involved in this disorder. [Copyright &y& Elsevier]