Characteristics of ictal EEG in Magnetic Seizure Therapy at various stimulation frequencies.

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.

Reduced Prefrontal Short-Latency Afferent Inhibition in Older Adults and Its Relation to Executive Function: A TMS-EEG Study.

Combining transcranial magnetic stimulation (TMS) with electroencephalography (EEG) allows for the assessment of various neurophysiological processes in the human cortex. One of these paradigms, short-latency afferent inhibition (SAI), is thought to be a sensitive measure of cholinergic activity. In a previous study, we demonstrated the temporal pattern of this paradigm from both the motor (M1) and dorsolateral prefrontal cortex (DLPFC) using simultaneous TMS-EEG recording. The SAI paradigm led to marked modulations at N100. In this study, we aimed to investigate the age-related effects on TMS-evoked potentials (TEPs) with the SAI from M1 and the DLPFC in younger (18-59 years old) and older (≥60 years old) participants. Older participants showed significantly lower N100 modulation in M1-SAI as well as DLPFC-SAI compared to the younger participants. Furthermore, the modulation of N100 by DLPFC-SAI in the older participants correlated with executive function as measured with the Trail making test. This paradigm has the potential to non-invasively identify cholinergic changes in cortical regions related to cognition in older participants.

Age and gender interactions in white matter of schizophrenia and obsessive compulsive disorder compared to non-psychiatric controls: commonalities across disorders.

Schizophrenia (SCZ) and obsessive-compulsive disorder (OCD) are psychiatric disorders with abnormalities in white matter structure. These disorders share high comorbidity and family history of OCD is a risk factor for SCZ which suggests some shared neurobiology. White matter was examined using diffusion tensor imaging in relativity large samples of SCZ (N = 48), OCD (N = 38) and non-psychiatric controls (N = 45). Fractional anisotropy (FA) was calculated and tract based spatial statistics were used to compare groups. In a whole brain analysis, SCZ and OCD both showed small FA reductions relative to controls in the corpus callosum. Both SCZ and OCD showed accelerated reductions in FA with age; specifically in the left superior longitudinal fasciculus in OCD, while the SCZ group demonstrated a more widespread pattern of FA reduction. Patient groups did not differ from each other in total FA or age effects in any regions. A general linear model using 13 a-priori regions of interest showed marginal group, group*gender, and group*age interactions. When OCD and SCZ groups were analyzed together, these marginal effects became significant (p < 0.05), suggesting commonalities exist between these patient groups. Overall, our results demonstrate a similar pattern of accelerated white matter decline with age and greater white matter deficit in females in OCD and SCZ, with overlap in the spatial pattern of deficits. There was no evidence for statistical differences in overall white matter between OCD and SCZ. Taken together, the results support the notion of shared neurobiology in SCZ and OCD.