Transcranial Magnetic Stimulation Device Research Articles

Brain state forecasting for precise brain stimulation: Current approaches and future perspectives.

Transcranial magnetic stimulation (TMS) has the potential to yield insights into cortical functions and improve the treatment of neurological and psychiatric conditions. However, its reliability is hindered by a low reproducibility of results. Among other factors, such low reproducibility is due to structural and functional variability between individual brains. Informing stimulation protocols with individual neuroimaging data could mitigate this issue, ensuring accurate targeting of structural brain areas and functional brain states in a subject-by-subject fashion. However, this process poses a set of theoretical and technical challenges. We focus on the problem of online functional targeting, which requires collecting electroencephalography (EEG) data, extracting brain states, and using them to trigger TMS in real time. This stream of operations introduces hardware and software delays in the real time set-up, such that brain states of interest may vanish before TMS delivery. To compensate for delays, it is necessary to process the EEG signal in real time, forecast it, and instruct TMS devices to target forecasted - rather than measured - brain states. Recently, this approach has been adopted successfully in a number of studies, opening interesting opportunities for personalised brain stimulation treatments. However, little has been done to explore and overcome the limitations of current forecasting methods. After reviewing the state of the art in brain state-dependent stimulation, we will discuss two broad classes of forecasting methods and their suitability for application to EEG time series. Subsequently, we will review the evidence in favour of data-driven forecasting and discuss its potential contributions to TMS methodology and the scientific understanding of brain dynamics, highlighting the transformative potential of big open datasets.

Ringing suppression design for pulse parameter controllable transcranial magnetic stimulation.

Pulse parameter controllable transcranial magnetic stimulation (cTMS) devices with fully-controlled semiconductor switches are increasingly being developed, but the primary waveform they generate is often accompanied by ringing, which is due to the resonance between the stimulation coil inductance and the snubber capacitors paired with the switches at the end of the pulse. This study provides a ringing suppression design method to effectively suppress it and reduce its impact on stimulation efficacy. A three-pronged design method is developed to suppress the ringing at its source. Firstly, laminated busbars are designed to connect main components, reducing parasitic inductance and thus decreasing the snubber energy requirement and the energy stored in the snubber capacitors, which is the main source of ringing energy. Secondly, the snubber circuit structure is improved by employing unidirectional snubber circuits to cut off the ringing loop. Lastly, a specially designed converter is used to transfer the energy stored in the snubber circuit, which to some extent represents the energy of the ringing, back to the cTMS storage capacitor. The suppressed ringing duration has been significantly reduced from around 1000μs to within 30μs. The proposed method effectively suppresses ringing, making the realized waveform much closer to the ideal waveform, which minimizes the impact of ringing on the stimulation effect and reduces the uncontrollable deviation between the actual activated region and the ideal target activation region. The method can be easily transferred to other cTMS devices, enhancing the controllability of stimulation efficacy.

Amelioration of biased neuronal differentiation in humanized mouse model of valproic acid‐induced autism by precisely targeted transcranial magnetic stimulation

AbstractAutism spectrum disorder (ASD) is a group of developmental diseases, which still lacks effective treatments. Pregnant exposure of Valproic acid (VPA) is an important environmental risk factor for ASD, but it's long‐term effects on the development of human neural cells, particularly in vivo, and the corresponding treatment have yet been fully investigated. In the present study, we first made a humanized ASD mouse model by transplanting VPA‐pretreated human neural progenitor cells (hNPCs) into the cortex of immune‐deficient mice. In comparison with wild type and control chimeric mice, ASD chimeric mice (VPAhNPC mice) exhibit core syndromes of ASD, namely dramatic reduction of sociability, social interaction and social communication, and remarkable increase of stereotype repetitive behaviors and anxiety‐like behaviors. At cellular level, VPA‐pretreatment biased the differentiation of human excitatory neurons and their axonal projections in host brain. Chemogenetic suppression of human neuronal activity restored most behavior abnormalities of VPAhNPC mice. Further, specific modulation of human neurons by a newly developed transcranial magnetic stimulation (TMS) device which could precisely target hPNCs effectively recued the core syndromes of ASD‐like behaviors, restored the excitatory‐inhibitory neuronal differentiation and axonal projection, and reversed the expression of over half of the VPA‐affected genes. These data demonstrated that VPAhNPC mice could be used as a humanized model of ASD and that precisely targeted TMS could ameliorate the VPA‐biased human neuronal differentiation in vivo.

Bidirectional regulation of motor circuits using magnetogenetic gene therapy.

Here, we report a magnetogenetic system, based on a single anti-ferritin nanobody-TRPV1 receptor fusion protein, which regulated neuronal activity when exposed to magnetic fields. Adeno-associated virus (AAV)-mediated delivery of a floxed nanobody-TRPV1 into the striatum of adenosine-2a receptor-Cre drivers resulted in motor freezing when placed in a magnetic resonance imaging machine or adjacent to a transcranial magnetic stimulation device. Functional imaging and fiber photometry confirmed activation in response to magnetic fields. Expression of the same construct in the striatum of wild-type mice along with a second injection of an AAVretro expressing Cre into the globus pallidus led to similar circuit specificity and motor responses. Last, a mutation was generated to gate chloride and inhibit neuronal activity. Expression of this variant in the subthalamic nucleus in PitX2-Cre parkinsonian mice resulted in reduced c-fos expression and motor rotational behavior. These data demonstrate that magnetogenetic constructs can bidirectionally regulate activity of specific neuronal circuits noninvasively in vivo using clinically available devices.

Abnormalities of cortical stimulation strength-duration time constant in amyotrophic lateral sclerosis

ObjectivesStrength-duration time constant (SDTC) may now be determined for cortical motor neurones, with activity mediated by transient Na+ conductances. The present study determined whether cortical SDTC is abnormal and linked to the pathogenesis of amyotrophic lateral sclerosis. MethodsCortical SDTC and rheobase were estimated from 17 ALS patients using a controllable pulse parameter transcranial magnetic stimulation (cTMS) device. Resting motor thresholds (RMTs) were determined at pulse widths (PW) of 30, 45, 60, 90 and 120 µs and M−ratio of 0.1, using a figure-of-eight coil applied to the primary motor cortex. ResultsSDTC was significantly reduced in ALS patients (150.58 ± 9.98 µs; controls 205.94 ± 13.7 µs, P < 0.01). The reduced SDTC correlated with a rate of disease progression (Rho = -0.440, P < 0.05), ALS functional rating score (ALSFRS-R) score (Rho = 0.446, P < 0.05), and disease duration (R = 0.428, P < 0.05). The degree of change in SDTC was greater in patients with cognitive abnormalities as manifested by an abnormal total Edinburgh Cognitive ALS Screen score (140.5 ± 28.7 µs, P < 0.001) and ALS-specific subscore (141.7 ± 33.2 µs, P = 0.003). ConclusionsCortical SDTC reduction was associated with a more aggressive ALS phenotype, or with more prominent cognitive impairment. SignificanceAn increase in transient Na+ conductances may account for the reduction in SDTC, linked to the pathogenesis of ALS.

Design and Testing of a Compact, Portable Single-Pulse Transcranial Magnetic Stimulation Device

Design and Testing of a Compact, Portable Single-Pulse Transcranial Magnetic Stimulation Device

Effectiveness of Transcranial Magnetic Stimulation in Patients after Ischemic Stroke: a Prospective Study

INTRODUCTION. Despite the fact that a large number of studies are focused on the rehabilitation of patients with ischemic stroke in the early recovery period, currently, much attention is paid to improving existing and developing new technologies in neurorehabilitation at the early stages of the disease. Transcranial magnetic stimulation (TMS) is a promising technology for the rehabilitation and recovery of patients with movement disorders after a stroke, which has a direct effect on the premotor cortex of the brain. AIM. To assess the effectiveness of TMS in relation to daily activity in a comprehensive medical rehabilitation program in patients with ischemic stroke in the early recovery period. MATERIALS AND METHODS. The study included 124 patients aged 55–75 years (53.2 % men and 46.8 % women). The main group included 64 people who received the TMS procedure. The comparison group included 60 patients who received an identical course of treatment, but instead of TMS, they underwent a low-intensity headband magnetic therapy. Treatment effectiveness was assessed using the Rivermead Mobility Index, Rehabilitation Routing Scales, and NIHSS. The severity of anxiety and depressive symptoms was assessed using the HADS scale. The total duration of treatment was 21 days. The dynamics of the patients’ condition was assessed before the start of treatment, 21 days after the course of rehabilitation and 3 months after the start of treatment. RESULTS. The main group showed a significant decrease in neurological deficit according to the NIHSS scale from 15.3 ± 3.6 to 10.1 ± 1.7 (p 0.05), Rivermead Mobility Index decreased from 5.6 ± 1.9 to 10.5 ± 2.4 (p 0.05) and Rehabilitation Routing Scale decreased from 4.3 ± 0.8 to 2.5 ± 0.5 points (p 0.05) since the start of rehabilitation and 3 months after its start. After 3 months, the neurological deficit in the main group was statistically significantly less compared to patients in the comparison group (p 0.5). A significant decrease in depressive symptoms was found in the main group (χ2 = 28.641; p 0.001), while in the control group the dynamics was not significant (χ2 = 7.140; p = 0.129); in addition, there was a regression of the anxiety component both in the main (χ2 = 47.949; p 0.001) and control (χ2 = 12.483; p = 0.015) groups. CONCLUSION. The use of the TMS device at the second stage of rehabilitation significantly reduces the neurological deficit, increases the mobility of patients, and reduces the severity of anxiety and depressive symptoms.

Investigating the electric field distribution in the human brain model induced by a high focality transcranial magnetic coil

Transcranial magnetic stimulation (TMS) is a noninvasive neuromodulation technique for treating various neurological disorders. The geometry of the TMS coil determines the focality, stimulation field strength, and stimulation depth of the induced electric field. In this paper, we introduce a novel coil, named the eccentric folding coil (EFC). We used Sim4Life, a three-dimensional human tissue medical electromagnetic simulation software, and the brain models of the subjects from the population head model repository to conduct finite element simulations of the eccentric folding coil, circular coil, and figure-eight coil, implying that the largest EFC has a focal area of 19.5 cm2 less than the smallest circular coil, and the EFC of any size has a smaller focal area than the figure-8 coil of the same size. Furthermore, we stimulated the model from three directions with the coil and measured the electric field responses of the model, confirming that stimulation varied in different directions. Additionally, we applied EFC to four representative human models and found that the electric field in different subjects’ brains differed by 3.03 mm in stimulation depth and 12.9 cm2 in focal area, suggesting that personalized human head modeling and electromagnetic analysis are essential for TMS treatment. In the future, we will explore using different types of TMS devices for patients with different conditions to achieve more precise and customized treatment.

Effect of Motor Imagery on Corticomotor Excitability and Pain Status in Rheumatoid Arthritis Patients.

Rheumatoid arthritis (RA) has been defined by the American College of Rheumatology in 1987 as a chronic inflammatory disease characterised by joint swelling, joint tenderness, and destruction of synovial joints leading to severe disability and premature mortality. There is a paucity of literature assessing corticomotor excitability in RA patients. This study aimed to assess the effect of motor imagery on corticomotor excitability and pain status in RA patients. The specific objectives were to study the effect of motor imagery on corticomotor excitability and pain status in RA patients. We also wanted to compare thecorticomotor excitability between RA patients with healthy controls. The correlation between the measures of corticomotor excitability and pain status in RA patients has also been done. The study was designed as a pilot clinical trial with a case-control design. Forty participants were recruited for the study. Twenty RA patients were recruited from the Department of Rheumatology and Department of Physical Medicine and Rehabilitation (PMR), AIIMS, New Delhi, and 20 healthy controls. Testing was performed at the Pain Research & rTMS Lab, Department of Physiology, AIIMS, New Delhi. The study was approved by the Institute Ethics Committee, AIIMS New Delhi, and registered in the Clinical Trials Registry-India (CTRI). For the subjective assessment of pain, the visual analogue scale (VAS), Short-Form McGill Pain Questionnaire, WHO-Quality of Life Brief questionnaire (WHO-QOL-BREF), and Rheumatoid Arthritis Pain Scale were used. For the objective assessment of pain, hot and cold pain thresholds were assessed using thermo-tactile quantitative sensory testing (QST) using the method of limits and corticomotor excitability using a transcranial magnetic stimulation device. All participants were also asked to perform motor imagery tasks which consisted of a metronome-paced thumb opposition paradigm. Results: The resting motor threshold (RMT) decreased significantly after motor imagery when compared to the mental calculation group. The amplitude of motor evoked potential (MEP) and QST parametervalue was comparable in both the groups before and after motor imagery and mental calculation. RMT was found to be significantly higher whereas MEP values were found to be significantly lower in RA compared to controls. We conclude that patients suffering from RA have decreased corticomotor excitability compared to controls. Motor imagery was effective in improving corticomotor excitability in these patients and can be used as rehabilitation in RA to relieve their pain.

The effect of pulse shape in theta-burst stimulation: Monophasic vs biphasic TMS

BackgroundIntermittent theta-burst stimulation (i) (TBS) is a transcranial magnetic stimulation (TMS) plasticity protocol. Conventionally, TBS is applied using biphasic pulses due to hardware limitations. However, monophasic pulses are hypothesised to recruit cortical neurons more selectively than biphasic pulses, predicting stronger plasticity effects. Monophasic and biphasic TBS can be generated using a custom-made pulse-width modulation-based TMS device (pTMS). ObjectiveUsing pTMS, we tested the hypothesis that monophasic iTBS would induce a stronger plasticity effect than biphasic, measured as induced increases in motor corticospinal excitability. MethodsIn a repeated-measures design, thirty healthy volunteers participated in three separate sessions, where monophasic and biphasic iTBS was applied to the primary motor cortex (M1 condition) or the vertex (control condition). Plasticity was quantified as increases in motor corticospinal excitability after versus before iTBS, by comparing peak-to-peak amplitudes of motor evoked potentials (MEP) measured at baseline and over 60 min after iTBS. ResultsBoth monophasic and biphasic M1 iTBS led to significant increases in MEP amplitude. As predicted, linear mixed effects (LME) models showed that the iTBS condition had a significant effect on the MEP amplitude (χ2 (1) = 27.615, p < 0.001) with monophasic iTBS leading to significantly stronger plasticity than biphasic iTBS (t (693) = 2.311, p = 0.021). Control vertex iTBS had no effect. ConclusionsIn this study, monophasic iTBS induced a stronger motor corticospinal excitability increase than biphasic within participants. This greater physiological effect suggests that monophasic iTBS may also have potential for greater functional impact, of interest for future fundamental and clinical applications of TBS.

A Brief History of Transcranial Magnetic Stimulation

A Brief History of Transcranial Magnetic Stimulation

History and Future Directions of rTMS for Treatment of Depressive Disorders

History and Future Directions of rTMS for Treatment of Depressive Disorders

Advancements in repetitive transcranial magnetic Stimulation for ischemic stroke rehabilitation

Despite significant improvements in acute stroke management, numerous stroke patients continue to experience wide-ranging disabilities, posing a severe global healthcare problem. Effective neuro-rehabilitation is critical for reduction of disability and improvement of life quality after stroke. Rapid developments in several post-ischemic stroke rehabilitation techniques, including magnetic, ultrasonic, optogenetic and electronic modalities, have been achieved in recent years. Repetitive transcranial magnetic stimulation has shown promising therapeutic efficacy in ischemic stroke rehabilitation during the last two decades. This review provides a detailed summary of the development, safety and efficacy of transcranial magnetic stimulation devices, current experimental models and mechanisms of repetitive transcranial magnetic stimulation in the context of ischemic stroke rehabilitation.

PLUSPULS: A transcranial magnetic stimulator with extended pulse protocols

Transcranial magnetic stimulation (TMS) is increasingly applied in basic neuroscience while its field of usage for diagnosing and treating various neurological diseases broadens steadily. A TMS device generates a current pulse in the reach of several thousand ampére to produce a magnetic pulse which induces an electric field around neurons. This electric field, if high enough to depolarize the neuron membrane, generates an action potential at the neuron which travels down the neurons connected to it. The PLUSPULS TMS generates this magnetic pulse by pre-charging a pulse capacitor C with the voltage VC0 and connecting it with a stimulation coil L. The oscillation of the resonance circuit is cut off after one period and is called a biphasic pulse. PLUSPULS is a high frequency stimulator with inter stimulus intervals (ISI) down to 1ms which enables different pulse protocols as paired pulse or quadri theta burst stimulation. A GUI on PC allows a flexible control of PLUSPULS with varying amplitudes and ISI in one burst. The modular hardware and the control via GUI on PC allows for an easier adjustment on requirements to come. The article provides design considerations, hardware, firmware and software to reconstruct a modular biphasic TMS with enhanced charging network to enable extended pulse protocols.

Modular pulse synthesizer for transcranial magnetic stimulation with fully adjustable pulse shape and sequence

The temporal shape of a pulse in transcranial magnetic stimulation (TMS) influences which neuron populations are activated preferentially as well as the strength and even direction of neuromodulation effects. Furthermore, various pulse shapes differ in their efficiency, coil heating, sensory perception, and clicking sound. However, the available TMS pulse shape repertoire is still very limited to a few biphasic, monophasic, and polyphasic pulses with sinusoidal or near-rectangular shapes. Monophasic pulses, though found to be more selective and stronger in neuromodulation, are generated inefficiently and therefore only available in simple low-frequency repetitive protocols. Despite a strong interest to exploit the temporal effects of TMS pulse shapes and pulse sequences, waveform control is relatively inflexible and only possible parametrically within certain limits. Previously proposed approaches for flexible pulse shape control, such as through power electronic inverters, have significant limitations: The semiconductor switches can fail under the immense electrical stress associated with free pulse shaping, and most conventional power inverter topologies are incapable of generating smooth electric fields or existing pulse shapes. Leveraging intensive preliminary work on modular power electronics, we present a modular pulse synthesizer (MPS) technology that can, for the first time, flexibly generate high-power TMS pulses (one-side peak ∼4000 V, ∼8000 A) with user-defined electric field shape as well as rapid sequences of pulses with high output quality. The circuit topology breaks the problem of simultaneous high power and switching speed into smaller, manageable portions, distributed across several identical modules. In consequence, the MPS TMS techology can use semiconductor devices with voltage and current ratings lower than the overall pulse voltage and distribute the overall switching of several hundred kilohertz among multiple transistors. MPS TMS can synthesize practically any pulse shape, including conventional ones, with fine quantization of the induced electric field (⩽17% granularity without modulation and ∼300 kHz bandwidth). Moreover, the technology allows optional symmetric differential coil driving so that the average electric potential of the coil, in contrast to conventional TMS devices, stays constant to prevent capacitive artifacts in sensitive recording amplifiers, such as electroencephalography. MPS TMS can enable the optimization of stimulation paradigms for more sophisticated probing of brain function as well as stronger and more selective neuromodulation, further expanding the parameter space available to users.

Anthropomorphic Brain Models Based on Magnetic Resonance Imaging

The article is devoted to the creation of a method for generating anthropomorphic brain models based on magnetic resonance imaging. The selection of the magnetic field amplitude for transcranial magnetic stimulation (TMS) is carried out through modeling using the finite element method (FEM). These FEM models graphically demonstrate information on the distribution of the magnetic field and, therefore, on the occurring neurophysiological and behavioral changes based on the dose of the TMS, the specific resistance of the head tissue and its anatomy. Thus, these models are an integral tool used to design, configure, and program TMS devices, as well as to study parameters such as magnetic field strength and tension. A distinctive aspect of this work is the quality of the resulting head models. When creating the calculated FEM models, an MRI image of the head was used to perform segmentation in the FreeSurfer environment. Next, the image was converted in the Matlab environment. After the assembly of the head model in COMSOL Multiphysics, the TMS was simulated. The results of the transformations is a head model made in the form of a three-dimensional grid, which is suitable for modeling. The obtained data can be used to personalize the TMS method in medicine.

TMS-Like Magnetic Fields Modulate Metabolic Activity of Hepatic and Colorectal Cancer Cells

Transcranial magnetic stimulation (TMS) is a widely available technology employing relatively strong (up to 4 T) pulsed (up to 300 Hz) magnetic fields for diagnostics of brain functions and treatment of various brain disorders. The current paradigm implies that the magnetic induction of Eddy currents in the brain neurons is the leading biological mechanism of TMS. At the same time, it is almost unknown how the TMS-like magnetic fields act on nonneuronal cells. Here, we explored the effects of TMS-like repetitive magnetic stimulation (RMS) on metabolic activity of human colorectal cancer (CRC) and hepatocellular carcinoma (HCC) cells. The HCT116 (CRC) and HuH7 (HCC) <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vitro</i> cell cultures were treated using a TMS device “Magstim Rapid <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ” with an air-cooled “Magstim” figure-eight coil (AFC70). Five intermittent RMS (iRMS) and two burst RMS (bRMS) experimental protocols were applied to the monolayers of the cells as a single treatment session. The activity of succinate dehydrogenase, an enzyme essential for energy production in mitochondria, was measured by 3(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) colorimetric viability assay in 24 h post-stimulation. Compared to untreated control, in HCT116 cells, a low-frequency iRMS treatment ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f $ </tex-math></inline-formula> = 1 Hz, 600 pulses, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$B $ </tex-math></inline-formula> = 0.8 T) induced a statistically significant decrease in metabolic activity (viability), while the high-frequency iRMS and bRMS increased it. In HuH7 cells, all tested RMS protocols either did not change or stimulated the metabolic activity (viability) of the cells, in comparison to the untreated control. The analysis of correlations revealed the almost opposite trends in CRC and HCC cells response to the frequency, temporal patterns, and magnetic field flux density considered as the parameters of the experimental RMS. Our findings demonstrate the tumor type- and stimulation protocol-specific effects of the repurposed TMS technology on colorectal and liver cancer cells. The underlying mechanism of these differences requires further study. The current results indicate that TMS-like magnetic fields may have new potential applications as an adjuvant anticancer treatment modality.

The Relation between Induced Electric Field and TMS-Evoked Potentials: A Deep TMS-EEG Study

Transcranial magnetic stimulation (TMS) in humans induces electric fields (E-fields, EF) that perturb and modulate the brain’s endogenous neuronal activity and result in the generation of TMS-evoked potentials (TEPs). The exact relation of the characteristics of the induced E-field and the intensity of the brains’ response, as measured by electroencephalography (EEG), is presently unclear. In this pilot study, conducted on three healthy subjects and two patients with generalized epilepsy (total: 3 males, 2 females, mean age of 26 years; healthy: 2 males, 1 female, mean age of 25.7 years; patients: 1 male, 1 female, mean age of 26.5 years), we investigated the temporal and spatial relations of the E-field, induced by single-pulse stimuli, and the brain’s response to TMS. Brain stimulation was performed with a deep TMS device (BrainsWay Ltd., Jerusalem, Israel) and an H7 coil placed over the central area. The induced EF was computed on personalized anatomical models of the subjects through magneto quasi-static simulations. We identified specific time instances and brain regions that exhibit high positive or negative associations of the E-field with brain activity. In addition, we identified significant correlations of the brain’s response intensity with the strength of the induced E-field and finally prove that TEPs are better correlated with E-field characteristics than with the stimulator’s output. These observations provide further insight in the relation between E-field and the ensuing cortical activation, validate in a clinically relevant manner the results of E-field modeling and reinforce the view that personalized approaches should be adopted in the field of non-invasive brain stimulation.

A neurostimulator system for real, sham, and multi-target transcranial magnetic stimulation

Objective. Transcranial magnetic stimulation (TMS) is a clinically effective therapeutic instrument used to modulate neural activity. Despite three decades of research, two challenging issues remain, the possibility of changing the (a) stimulated spot and (b) stimulation type (real or sham) without physically moving the coil. In this study, a second-generation programmable TMS device with advanced stimulus shaping is introduced that uses a five-level cascaded H-bridge inverter and phase-shifted pulse-width modulation. The principal idea of this research is to obtain real, sham, and multi-locus stimulation using the same TMS system. Approach. We propose a two-channel modulation-based magnetic pulse generator and a novel coil arrangement, consisting of two circular coils with a physical distance of 20 mm between the coils and a control method for modifying the effective stimulus intensity, which leads to the live steerability of the target and type of stimulation. Main results. Based on the measured system performance, the stimulation profile can be steered ±20 mm along a line from the centroid of the coil locations by modifying the modulation index. Significance. The proposed system supports electronic control of the stimulation spot without physical coil movement, resulting in tunable modulation of targets, which is a crucial step towards automated TMS machines.

TAP: targeting and analysis pipeline for optimization and verification of coil placement in transcranial magnetic stimulation

Objective. Transcranial magnetic stimulation (TMS) can modulate brain function via an electric field (E-field) induced in a brain region of interest (ROI). The ROI E-field can be computationally maximized and set to match a specific reference using individualized head models to find the optimal coil placement and stimulus intensity. However, the available software lacks many practical features for prospective planning of TMS interventions and retrospective evaluation of the experimental targeting accuracy. Approach. The TMS targeting and analysis pipeline (TAP) software uses an MRI/fMRI-derived brain target to optimize coil placement considering experimental parameters such as the subject’s hair thickness and coil placement restrictions. The coil placement optimization is implemented in SimNIBS 3.2, for which an additional graphical user interface (TargetingNavigator) is provided to visualize/adjust procedural parameters. The coil optimization process also computes the E-field at the target, allowing the selection of the TMS device intensity setting to achieve specific E-field strengths. The optimized coil placement information is prepared for neuronavigation software, which supports targeting during the TMS procedure. The neuronavigation system can record the coil placement during the experiment, and these data can be processed in TAP to quantify the accuracy of the experimental TMS coil placement and induced E-field. Main results. TAP was demonstrated in a study consisting of three repetitive TMS sessions in five subjects. TMS was delivered by an experienced operator under neuronavigation with the computationally optimized coil placement. Analysis of the experimental accuracy from the recorded neuronavigation data indicated coil location and orientation deviations up to about 2 mm and 2°, respectively, resulting in an 8% median decrease in the target E-field magnitude compared to the optimal placement. Significance. TAP supports navigated TMS with a variety of features for rigorous and reproducible stimulation delivery, including planning and evaluation of coil placement and intensity selection for E-field-based dosing.