Optimizing TMS Coil Placement Approaches for Targeting the Dorsolateral Prefrontal Cortex in Depressed Adolescents: An Electric Field Modeling Study

Dosimetry for repetitive transcranial magnetic stimulation: a translational study from Alzheimer's disease patients to controlledin vitroinvestigations

Objective.Recent studies have indicated that repetitive transcranial magnetic stimulation (rTMS) could enhance cognition in Alzheimer's Disease (AD) patients, but to now the molecular-level interaction mechanisms driving this effect remain poorly understood. While cognitive scores have been the primary measure of rTMS effectiveness, employing molecular-based approaches could offer more precise treatment predictions and prognoses. To reach this goal, it is fundamental to assess the electric field (E-field) and the induced current densities (J) within the stimulated brain areas and to translate these values toin vitrosystems specifically devoted in investigating molecular-based interactions of this stimulation.Approach.This paper offers a methodological procedure to guide dosimetric assessment to translate the E-field induced in humans (in a specific pilot study) intoin vitrosettings. Electromagnetic simulations on patients' head models and cellular holders were conducted to characterize exposure conditions and determine necessary adjustments forin vitroreplication of the same dose delivered in humans using the same stimulating coil.Main results.Our study highlighted the levels of E-field andJinduced in the target brain region and showed that the computed E-field andJwere different among patients that underwent the treatment, so to replicate the exposure to thein vitrosystem, we have to consider a range of electric quantities as reference. To match the E-field to the levels calculated in patients' brains, an increase of at least the 25% in the coil feeding current is necessary whenin vitrostimulations are performed. Conversely, to equalize current densities, modifications in the cells culture medium conductivity have to be implemented reducing it to one fifth of its value.Significance.This dosimetric assessment and subsequent experimental adjustments are essential to achieve controlledin vitroexperiments to better understand rTMS effects on AD cognition. Dosimetry is a fundamental step for comparing the cognitive effects with those obtained by stimulating a cellular model at an equal dose rigorously evaluated.

A New Angle on Transcranial Magnetic Stimulation Coil Orientation: A Targeted Narrative Review

Transcranial magnetic stimulation (TMS) is used to treat several neuropsychiatric disorders including depression, where it is effective in approximately one half of patients for whom pharmacological approaches have failed. Treatment response is related to stimulation parameters such as the stimulation frequency, pattern, intensity, location, total number of pulses and sessions applied, and target brain network engagement. One critical but underexplored component of the stimulation procedure is the orientation or yaw angle of the commonly used figure-of-eight TMS coil, which is known to impact neuronal response to TMS. However, coil orientation has remained largely unchanged since TMS was first used to treat depression and continues to be based on motor cortex anatomy, which may not be optimal for the dorsolateral prefrontal cortex treatment site. In this targeted narrative review, we evaluate experimental, clinical, and computational evidence indicating that optimizing coil orientation may improve TMS treatment outcomes. The properties of the electric field induced by TMS, the changes to this field caused by the differing conductivities of head tissues, and the interaction between coil orientation and the underlying cortical anatomy are summarized. We describe evidence that the magnitude and site of cortical activation, surrogate markers of TMS dosing and brain network targeting considered central in clinical response to TMS, are influenced by coil orientation. We suggest that coil orientation should be considered when applying therapeutic TMS and propose several approaches to optimizing this potentially important treatment parameter.

A semi-automated pipeline for finite element modeling of electric field induced in nonhuman primates by transcranial magnetic stimulation

BACKGROUND

Transcranial magnetic stimulation (TMS) is used to treat a range of brain disorders by inducing an electric field (E-field) in the brain. However, the precise neural effects of TMS are not well understood. Nonhuman primates (NHPs) are used to model the impact of TMS on neural activity, but a systematic method of quantifying the induced E-field in the cortex of NHPs has not been developed.

NEW METHOD

The pipeline uses statistical parametric mapping (SPM) to automatically segment a structural MRI image of a rhesus macaque into five tissue compartments. Manual corrections are necessary around implants. The segmented tissues are tessellated into 3D meshes used in finite element method (FEM) software to compute the TMS induced E-field in the brain. The gray matter can be further segmented into cortical laminae using a volume preserving method for defining layers.

RESULTS

Models of three NHPs were generated with TMS coils placed over the precentral gyrus. Two coil configurations, active and sham, were simulated and compared. The results demonstrated a large difference in E-fields at the target. Additionally, the simulations were calculated using two different E-field solvers and were found to not significantly differ.

COMPARISON WITH EXISTING METHODS

Current methods segment NHP tissues manually or use automated methods for only the brain tissue. Existing methods also do not stratify the gray matter into layers.

CONCLUSION

The pipeline calculates the induced E-field in NHP models by TMS and can be used to plan implant surgeries and determine approximate E-field values around neuron recording sites.

Safety of noninvasive brain stimulation in children

PURPOSE OF REVIEW

Noninvasive brain stimulation (NIBS) is a promising method for altering cortical excitability with clinical implications. It has been increasingly used in children, especially in neurodevelopmental disorders. Yet, its safety and applications in the developing brain require further investigation. This review aims to provide an overview of the safety of commonly used NIBS techniques in children, including transcranial electrical stimulation (tES) and transcranial magnetic stimulation (TMS). Safety data for other NIBS methods is not reported in this review.

RECENT FINDINGS

In line with studies from the last decade, findings in the last 2 years (2022-2023) support the safety of NIBS in children and adolescents within the currently applied protocols. Both tES and TMS are well tolerated, if safety rules, including exclusion criteria, are applied.

SUMMARY

We briefly discussed developmental aspects of stimulation parameters that need to be considered in the developing brain and provided an up-to-date overview of tES/TMS applications in children and adolescents. Overall, the safety profile of tES/TMS in children is good. For both the tES and TMS applications, epilepsy and active seizure disorder should be exclusion criteria to prevent potential seizures. Using child-sized earplugs is required for TMS applications. We lack large randomized double-blind trialsand longitudinal studies to establish the safety of NIBS in children.

VIDEO ABSTRACT

http://links.lww.com/YCO/A78 .

Treatment-Resistant Depression in America Latina study: one-year follow-up of treatment resistant depression patients under standard of care reveals insights on quality of life, disability, work impairment, and depressive symptoms

Introduction

Depressive Disorders are on the rise worldwide. This is also the case in Latin America (LatAm). Treatment-Resistant Depressive Disorder (TRD) poses additional burden to patients with depression. Impacts quality of life (QoL) and other dimensions, and standard of care (SOC) is insufficient to achieve the desired clinical outcomes. Evidence from LatAm is, however, lacking. The present study was devised as a 1-year follow-up of the SOC in TRD patients in LatAm to explore the burden of TRD.

Methods

This was an observational, multinational, longitudinal study. Patients with clinical diagnosis of TRD in LatAm were included in a 1-year follow-up with SOC. Beyond the Sociodemographic characterization, outcome measures were QoL (EQ-5D-5L), disability (Sheehan Disability Scale - SDS), work productivity (Work Productivity and Activity Incapacity Questionnaire: depression - WPAI:D) and depression severity (Patient Health Questionnaire-PHQ9). Patients were assessed every 3-months and comparison was performed based on change from baseline to each visit and end of study (EOS - 12 months).

Results

Patients averaged 48 (± 13.12) years, mostly female (80.9%) and married/consensual union (42.5%) or single patients (34.4%). Despite the SOC treatment, three-quarters of the patients remained symptomatic at EOS, regardless of the significant longitudinal decrease (p ≤ 0.001). Similar trends were found for disability (p ≤ 0.001) -82.2% of the patients reporting work/school disruption at EOS-, percentage of work (34%) and activity impairment (40%) at EOS (p ≤ 0.001) and only 29.2% of patients with depressive severity "none" at EOS (p ≤ 0.001). The results portray the need to improve clinical outcomes in this complex and burdensome disease in LatAm.

Discussion

Here we show that the burden of TRD remains significant in essential dimensions of everyday life at EOS underlining the need for better therapeutic solutions. The improvements in most patients do not provide the desired outcome of return to the state before the condition. Further research should focus on identifying which treatments provide better outcomes in a real-world context.