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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]

• Baseline resting EEG theta connectivity and alpha power predicted response to rTMS for depression in our previous research. • These measures did not differentiate responders and non-responders in a larger independent dataset. • Theta connectivity and alpha power are unlikely to be clinically useful predictors of response to rTMS for depression. Our previous research showed high predictive accuracy at differentiating responders from non-responders to repetitive transcranial magnetic stimulation (rTMS) for depression using resting electroencephalography (EEG) and clinical data from baseline and one-week following treatment onset using a machine learning algorithm. In particular, theta (4–8 Hz) connectivity and alpha power (8–13 Hz) significantly differed between responders and non-responders. Independent replication is a necessary step before the application of potential predictors in clinical practice. This study attempted to replicate the results in an independent dataset. We submitted baseline resting EEG data from an independent sample of participants who underwent rTMS treatment for depression (N = 193, 128 responders) (Krepel et al., 2018) to the same between group comparisons as our previous research (Bailey et al., 2019). Our previous results were not replicated, with no difference between responders and non-responders in theta connectivity (p = 0.250, Cohen's d = 0.1786) nor alpha power (p = 0.357, η p 2 = 0.005). These results suggest that baseline resting EEG theta connectivity or alpha power are unlikely to be generalisable predictors of response to rTMS treatment for depression. These results highlight the importance of independent replication, data sharing and using large datasets in the prediction of response research. [ABSTRACT FROM AUTHOR]

Objectives The first objective of this study aimed to elucidate the relationship between seizure characteristics and Magnetic Seizure Therapy (MST) treatment outcome. The second objective was to determine the effect of stimulation frequency on seizure characteristics. Methods Using a between-subjects design, we compared the seizures of patients with unipolar depression receiving MST at three separate stimulation frequencies: 25 Hz ( n  = 34), 50 Hz ( n  = 16) and 100 Hz ( n  = 11). Seizures were rated for overall seizure adequacy on a scale of 0–6, with one point given for each measure that was considered to be adequate according to the ECT literature: (1) seizure EEG duration (2) motor duration, (3) post-ictal suppression, (4) ictal EEG maximum amplitude, (5) Global Seizure Strength, and (6) Symmetry. Mixed-effect models were used to evaluate the effect of frequency on seizure characteristics and the relationships between seizure characteristics and clinical outcome. Results (1) 100 Hz induced seizures that were less adequate than seizures induced with 50 Hz and 25 Hz stimulations. Seizures induced by 50 Hz stimulations had longer slow-wave phase durations and total EEG durations than the 100 Hz and 25 Hz groups. Global seizure strength was less robust in seizures induced by 100 Hz MST compared to the other stimulation frequencies. (2) Shorter polyspike durations and smaller slow-wave amplitude predicted reductions in overall symptoms of depression as measured by the 24-item Hamilton Depression Scale. Conclusion Analysis of our first objective revealed stimulation frequency significantly influences measures of overall seizure adequacy. However, our results also revealed these descriptions of seizure adequacy based on ECT literature may not be useful for MST-induced seizures, as the characteristics of MST-induced seizure characteristics may predict clinical response in a different manner. Significance These results may help to distinguish the biological processes impacted by stimulation frequency and may suggest different mechanisms of action between convulsive therapies and challenge the current understanding of seizure adequacy for MST. [ABSTRACT FROM AUTHOR]