Browsing by Author "Peterchev, Angel V"
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Item Open Access Advances in Transcranial Magnetic Stimulation Technology(2015-06-05) Peterchev, Angel V; Deng, Zhi-De; Goetz, Stefan© 2015 by Wiley-Blackwell. All rights reserved. This chapter provides overview of the state of the art of transcranial magnetic stimulation (TMS) devices, including pulse sources with flexible control of the output waveform parameters and a wide variety of coil designs. It discusses technologies for accurate TMS targeting, including electric field models, frameless stereotaxy, and robotic coil holders. The chapter addresses technological aspects of ancillary coil effects such as heating, noise, vibration, and scalp stimulation. TMS requires high energy pulses that present a technical challenge for the design of practical, flexible, and efficient pulse sources. The chapter covers technical considerations for the integration of TMS and neuroimaging devices. It discusses various coil configurations and their electric field characteristics as well as technical advances in coil field modelling, positioning systems, efficiency and cooling, noise and scalp stimulation, and sham. The chapter summarizes technical considerations for the integration of TMS and neuroimaging devices.Item Open Access Application of long-interval paired-pulse transcranial magnetic stimulation to motion-sensitive visual cortex does not lead to changes in motion discrimination.(Neuroscience letters, 2020-05-12) Gamboa, Olga Lucia; Brito, Alexandra; Abzug, Zachary; D'Arbeloff, Tracy; Beynel, Lysianne; Wing, Erik A; Dannhauer, Moritz; Palmer, Hannah; Hilbig, Susan A; Crowell, Courtney A; Liu, Sicong; Donaldson, Rachel; Cabeza, Roberto; Davis, Simon W; Peterchev, Angel V; Sommer, Marc A; Appelbaum, Lawrence GThe perception of visual motion is dependent on a set of occipitotemporal regions that are readily accessible to neuromodulation. The current study tested if paired-pulse Transcranial Magnetic Stimulation (ppTMS) could modulate motion perception by stimulating the occipital cortex as participants viewed near-threshold motion dot stimuli. In this sham-controlled study, fifteen subjects completed two sessions. On the first visit, resting motor threshold (RMT) was assessed, and participants performed an adaptive direction discrimination task to determine individual motion sensitivity. During the second visit, subjects performed the task with three difficulty levels as TMS pulses were delivered 150 and 50 ms prior to motion stimulus onset at 120% RMT, under the logic that the cumulative inhibitory effect of these pulses would alter motion sensitivity. ppTMS was delivered at one of two locations: 3 cm dorsal and 5 cm lateral to inion (scalp-based coordinate), or at the site of peak activation for "motion" according to the NeuroSynth fMRI database (meta-analytic coordinate). Sham stimulation was delivered on one-third of trials by tilting the coil 90°. Analyses showed no significant active-versus-sham effects of ppTMS when stimulation was delivered to the meta-analytic (p = 0.15) or scalp-based coordinates (p = 0.17), which were separated by 29 mm on average. Active-versus-sham stimulation differences did not interact with either stimulation location (p = 0.12) or difficulty (p = 0.33). These findings fail to support the hypothesis that long-interval ppTMS recruits inhibitory processes in motion-sensitive cortex but must be considered within the limited parameters used in this design.Item Open Access Flexible Modular Power Electronics for High-Power Medical and Energy Applications(2021) Li, ZhongxiPower electronics is a technology that converts electric power between different temporal shapes and amplitudes of current and voltage. In the past decades, most applications evolved towards simpler circuit topologies thanks to the rapid advancement of power semiconductors. As such, developments of modern power converters are typically at the mercy of the transistors’ capabilities, often entailing customizations and thus large upfront investment as well as delayed market entry. Meanwhile, the existing power transistor lineup started to fall behind some emerging demands in simultaneously high power, high quality, and high output bandwidth. Examples include modern magnetic neural stimulator, high-power audio amplifier, and high-end motor testbench for electric vehicles. This work addresses the above problems through cascaded structures––a modular circuit backbone with flexibility and scalability at heart. With a plurality of circuit modules, it surprises none that the cascaded structure can outperform existing solutions. We therefore also focus on reducing the effort and cost of the adoption, which often encounters surprising hesitance from the industry and even academia despite clear advantages or being the only viable solution to certain problems. Specifically, we focus on 1) simplifying the module voltage balancing, 2) mitigating the pulsating power of the cascaded structure, 3) reducing the number of power sources, 4) synthesizing high-fidelity output with fewest possible modules, and 5) circuit layout based on printed-circuit boards. To this end, modifications are done with liberty but with extra caution on the power efficiency, cost, and practicality. In Chapter 2 we present a type of cascaded modular converter that trivializes the module balancing, thus shaving off a great portion of cost of the cascaded converters in general. The new converter, together with proposed control methods, mitigates the pulsating power in energy applications, as is shown in Chapter 3. Chapter 4 demonstrates the world’s first magnetic neural stimulator with fully flexible waveforms. The stimulator, implemented in the cascaded structure, greatly benefits from the novel charging control, which obviates multiple expensive power supplies. Finally, the aforementioned novelties culminate as a high fidelity, high bandwidth power amplifier in Chapter 5, where hundreds of output levels are produced from only a handful of modules under any load conditions.
Item Open Access Intensity- and timing-dependent modulation of motion perception with transcranial magnetic stimulation of visual cortex.(Neuropsychologia, 2020-10) Gamboa Arana, Olga Lucia; Palmer, Hannah; Dannhauer, Moritz; Hile, Connor; Liu, Sicong; Hamdan, Rena; Brito, Alexandra; Cabeza, Roberto; Davis, Simon W; Peterchev, Angel V; Sommer, Marc A; Appelbaum, Lawrence GDespite the widespread use of transcranial magnetic stimulation (TMS) in research and clinical care, the dose-response relations and neurophysiological correlates of modulatory effects remain relatively unexplored. To fill this gap, we studied modulation of visual processing as a function of TMS parameters. Our approach combined electroencephalography (EEG) with application of single pulse TMS to visual cortex as participants performed a motion perception task. During each participants' first visit, motion coherence thresholds, 64-channel visual evoked potentials (VEPs), and TMS resting motor thresholds (RMT) were measured. In second and third visits, single pulse TMS was delivered at one of two latencies, either 30 ms before the onset of motion or at the onset latency of the N2 VEP component derived from the first session. TMS was delivered at 0%, 80%, 100%, or 120% of RMT over the site of N2 peak activity, or at 120% over vertex. Behavioral results demonstrated a significant main effect of TMS timing on accuracy, with better performance when TMS was applied at the N2-Onset timing versus Pre-Onset, as well as a significant interaction, indicating that 80% intensity produced higher accuracy than other conditions at the N2-Onset. TMS effects on the P3 VEP showed reduced amplitudes in the 80% Pre-Onset condition, an increase for the 120% N2-Onset condition, and monotonic amplitude scaling with stimulation intensity. The N2 component was not affected by TMS. These findings reveal the influence of TMS intensity and timing on visual perception and electrophysiological responses, with optimal facilitation at stimulation intensities below RMT.Item Open Access Multi-Scale Modeling for Analysis and Design of Transcranial Electric and Magnetic Brain Stimulation(2021) Aberra, Aman SenayTranscranial electric stimulation (tES) and magnetic stimulation (TMS) can noninvasively modulate brain activity in humans, offering broad research and therapeutic applications. However, improving the efficacy and selectivity of these techniques is challenging without a mechanistic understanding of how the stimulation parameters determine the neural response and how these parameters can be manipulated to activate specific neural circuits. This dissertation presents multiscale computational models that predict the neural response to TMS and tES at the single-cell and population levels for analysis and rational design of transcranial brain stimulation.We adapted biophysically-realistic models of cortical neurons from the Blue Brain network to the properties of mature rat and human neurons and characterized the direct response to extracellular stimulation with both subthreshold and suprathreshold electric field (E-field) stimulation modalities. These models included 3D reconstructed axonal and dendritic arbors as well as multiple excitatory and inhibitory cell types with validated electrophysiological behavior. Axon terminals were the lowest threshold elements for stimulation, and their dependence on threshold and polarization was determined by cell-type specific morphological features, such as myelination, diameter, and branching. However, we found for TMS pulse waveforms specifically, activation thresholds were higher than expected from in vivo applications. We improved the fidelity of the axon models further using a feature-based optimization algorithm, but these modifications did not produce models with significantly lower thresholds, suggesting other factors may allow for suprathreshold activation at the E-field intensities induced experimentally. The neuron models were then embedded in anatomically-realistic volume conductor head models of the E-field in humans derived from magnetic resonance imaging (MRI) data to simulate the direct neural response to TMS and tDCS. The models reproduced relative trends in motor thresholds as well as the experimentally-measured strength–duration time constant. TMS activated with lowest intensity intracortical axon terminals in the superficial gyral crown and lip region, proportional to the E-field magnitude. Thresholds were lowest for the L5 pyramidal cells (PCs), with activation of the L2/3 PCs and large basket cells at most intensities. Reversing the pulse direction revealed waveform-dependent spatial shifts in the activated neural population that may explain experimentally observed differences in the latencies and thresholds of muscle responses to TMS of motor cortex. We also quantified the subthreshold polarization generated by conventional tDCS with large rectangular pad electrodes and 4×1 high definition (HD) tDCS electrodes targeting the motor hand knob. Axonal and dendritic terminal polarization was higher than somatic polarization in all cell types, and polarization trends between cell types varied by subcellular compartment. While the HD tDCS montage produced a significantly more focal E-field within the brain, both montages generated broad regions of depolarization and hyperpolarization beneath the electrodes. These simulations demonstrated the importance of coupling the E-field to neuron models incorporating non-linear membrane dynamics and realistic morphologies for predicting the neural response to TMS and tES. Indeed, extrapolating the neural response (polarization or threshold) from the uniform E-field or macroscopic E-field components often led to erroneous predictions. Due to the high computational cost of these biophysically-realistic models, we also developed rapid estimators of the neural response using a 3D convolutional neural network. This approach allowed for reproducing the threshold distributions of the realistic model neurons with several orders of magnitude shorter run times than using the E-field distribution alone. In sum, this work provides both computational tools and mechanistic insights to improve the use and development of transcranial magnetic and electrical stimulation technologies.
Item Open Access Simultaneous transcranial magnetic stimulation and single-neuron recording in alert non-human primates.(Nat Neurosci, 2014-08) Mueller, Jerel K; Grigsby, Erinn M; Prevosto, Vincent; Petraglia, Frank W; Rao, Hrishikesh; Deng, Zhi-De; Peterchev, Angel V; Sommer, Marc A; Egner, Tobias; Platt, Michael L; Grill, Warren MTranscranial magnetic stimulation (TMS) is a widely used, noninvasive method for stimulating nervous tissue, yet its mechanisms of effect are poorly understood. Here we report new methods for studying the influence of TMS on single neurons in the brain of alert non-human primates. We designed a TMS coil that focuses its effect near the tip of a recording electrode and recording electronics that enable direct acquisition of neuronal signals at the site of peak stimulus strength minimally perturbed by stimulation artifact in awake monkeys (Macaca mulatta). We recorded action potentials within ∼1 ms after 0.4-ms TMS pulses and observed changes in activity that differed significantly for active stimulation as compared with sham stimulation. This methodology is compatible with standard equipment in primate laboratories, allowing easy implementation. Application of these tools will facilitate the refinement of next generation TMS devices, experiments and treatment protocols.Item Open Access Site-Specific Effects of Online rTMS during a Working Memory Task in Healthy Older Adults.(Brain sciences, 2020-04-27) Beynel, Lysianne; Davis, Simon W; Crowell, Courtney A; Dannhauer, Moritz; Lim, Wesley; Palmer, Hannah; Hilbig, Susan A; Brito, Alexandra; Hile, Connor; Luber, Bruce; Lisanby, Sarah H; Peterchev, Angel V; Cabeza, Roberto; Appelbaum, Lawrence GThe process of manipulating information within working memory is central to many cognitive functions, but also declines rapidly in old age. Improving this process could markedly enhance the health-span in older adults. The current pre-registered, randomized and placebo-controlled study tested the potential of online repetitive transcranial magnetic stimulation (rTMS) applied at 5 Hz over the left lateral parietal cortex to enhance working memory manipulation in healthy elderly adults. rTMS was applied, while participants performed a delayed-response alphabetization task with two individually titrated levels of difficulty. Coil placement and stimulation amplitude were calculated from fMRI activation maps combined with electric field modeling on an individual-subject basis in order to standardize dosing at the targeted cortical location. Contrary to the a priori hypothesis, active rTMS significantly decreased accuracy relative to sham, and only in the hardest difficulty level. When compared to the results from our previous study, in which rTMS was applied over the left prefrontal cortex, we found equivalent effect sizes but opposite directionality suggesting a site-specific effect of rTMS. These results demonstrate engagement of cortical working memory processing using a novel TMS targeting approach, while also providing prescriptions for future studies seeking to enhance memory through rTMS.Item Open Access Transcranial magnetic stimulation: the road to clinical therapy for dystonia(Dystonia) Mulcahey, Patrick J; Peterchev, Angel V; Calakos, Nicole; Bukhari-Parlakturk, NoreenDespite many research studies, transcranial magnetic stimulation (TMS) is not yet an FDA-approved clinical therapy for dystonia patients. This review describes the four major challenges that have historically hindered the clinical translation of TMS. The four challenges described are limited types of clinical trial designs, limited evidence on objective behavioral measures, variability in the TMS clinical response, and the extensive TMS parameters to optimize for clinical therapy. Progress has been made to diversify the types of clinical trial design available to clinical researchers, identify evidence-based objective behavioral measures, and reduce the variability in TMS clinical response. Future studies should identify objective behavioral measures for other dystonia subtypes and expand the optimal TMS stimulation parameters for clinical therapy. Our review highlights the key progress made to overcome these barriers and gaps that remain for TMS to develop into a long-lasting clinical therapy for dystonia patients.