Planar figure-8 coils for ultra-focal and directional micromagnetic brain stimulation

Jeong, Hongbae; Deng, Jiangdong; Bonmassar, Giorgio

doi:10.1116/6.0001281

Cited by 7 publications

(10 citation statements)

References 25 publications

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“…However, these fields were estimated and reported on the tip of the coil and not inside the tissue. A figure-of-8 geometry could be used to augment the resulting E-field strength, and our previous work demonstrated that the figure-of-8 coil geometry could generate the enhanced E-field (Jeong et al, 2021).…”

Section: Discussionmentioning

confidence: 99%

“…Furthermore, we were not able to study µMS response with greater intensities and pulse durations due to limitations in the thin film construction of Murata's surface mount inductor, which resulted in fusing (see Supplementary Information S4). In future work, we plan to create a custommade microscopic magnetic stimulation device (Jeong et al, 2021) that will address this limitation. Finally, we were not able to rotate the µM-VNS coil around the vagus nerve because the current surface mount device could only be positioned underneath the vagus nerve.…”

Section: Limitationsmentioning

confidence: 99%

“…µMS induces a solenoidal electric field without placing the metallic micro-coil in direct contact with the tissue, generating closed-loop circular currents (Mukesh et al, 2017) and achieving a high spatial focality (Jeong et al, 2021). In µMS, no net charge is transferred from the electrode into tissue since no sinks or sources are generated when a time-varying magnetic field induces a current density.…”

Section: Introductionmentioning

confidence: 99%

“…Large fibers were clustered using the k-mean clustering algorithm (Lloyd, 1982) since multiple fibers branch to different organs, such as the heart. Based on our previous modeling results (Jeong et al, 2021), a planar spiral coil microscopic dimension was chosen (Figure 1C). Numerical studies were conducted (Figure 1D) to estimate the µMS's optimal orientation and pulse strength.…”

Section: Introductionmentioning

confidence: 99%

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Short-pulsed micro-magnetic stimulation of the vagus nerve

Jeong

Cho

et al. 2022

Front. Physiol.

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Vagus nerve stimulation (VNS) is commonly used to treat drug-resistant epilepsy and depression. The therapeutic effect of VNS depends on stimulating the afferent vagal fibers. However, the vagus is a mixed nerve containing afferent and efferent fibers, and the stimulation of cardiac efferent fibers during VNS may produce a rare but severe risk of bradyarrhythmia. This side effect is challenging to mitigate since VNS, via electrical stimulation technology used in clinical practice, requires unique electrode design and pulse optimization for selective stimulation of only the afferent fibers. Here we describe a method of VNS using micro-magnetic stimulation (µMS), which may be an alternative technique to induce a focal stimulation, enabling a selective fiber stimulation. Micro-coils were implanted into the cervical vagus nerve in adult male Wistar rats. For comparison, the physiological responses were recorded continuously before, during, and after stimulation with arterial blood pressure (ABP), respiration rate (RR), and heart rate (HR). The electrical VNS caused a decrease in ABP, RR, and HR, whereas µM-VNS only caused a transient reduction in RR. The absence of an HR modulation indicated that µM-VNS might provide an alternative technology to VNS with fewer heart-related side effects, such as bradyarrhythmia. Numerical electromagnetic simulations helped estimate the optimal coil orientation with respect to the nerve to provide information on the electric field’s spatial distribution and strength. Furthermore, a transmission emission microscope provided very high-resolution images of the cervical vagus nerve in rats, which identified two different populations of nerve fibers categorized as large and small myelinated fibers.

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Section: Discussionmentioning

confidence: 99%

Section: Limitationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Short-pulsed micro-magnetic stimulation of the vagus nerve

Jeong

Cho

et al. 2022

Front. Physiol.

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“…To further increase the focality of μMS and the directionality of the neural response, researchers in the μMS field have started to explore the possibility of combining multiple coils to increase stimulation effectiveness. Jeong et al (2021) designed a figure-eight spiral micro-coil to generate high magnetic flux for ultra-focal stimulation. Saito constructed a figure-eight micro-coil using commercially available chip inductors, which effectively suppressed synchronized bursting activity in a cultured neural network ( Saito, 2021 ).…”

Section: Introductionmentioning

confidence: 99%

Improving focality and consistency in micromagnetic stimulation

Hall

Hendee

2023

Front. Comput. Neurosci.

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The novel micromagnetic stimulation (μMS) technology aims to provide high resolution on neuronal targets. However, consistency of neural activation could be compromised by a lack of surgical accuracy, biological variation, and human errors in operation. We have recently modeled the activation of an unmyelinated axon by a circular micro-coil. Although the coil could activate the axon, its performance sometimes lacked focality and consistency. The site of axonal activation could shift by several experimental factors, including the reversal of the coil current, displacement of the coil, and changes in the intensity of the stimulation. Current clinical practice with transcranial magnetic stimulation (TMS) has suggested that figure-eight coils could provide better performance in magnetic stimulation than circular coils. Here, we estimate the performance of μMS by a figure-eight micro-coil, by exploring the impact of the same experimental factors on its focality and consistency in axonal activation. We derived the analytical expression of the electric field and activating function generated by the figure-eight micro-coil, and estimated the location of axonal activation. Using NEURON modeling of an unmyelinated axon, we found two different types (A and B) of axon activation by the figure-eight micro-coil, mediated by coil currents of reversed direction. Type A activation is triggered by membrane hyperpolarization followed by depolarization; Type B activation is triggered by direct membrane depolarization. Consequently, the two types of stimulation are governed by distinct ion channel mechanisms. In comparison to the circular micro-coil, the figure-eight micro-coil requires significantly less current for axonal activation. Under figure-eight micro-coil stimulation, the site of axonal activation does not change with the reversal of the coil current, displacement of the coil, or changes in the intensity of the stimulation. Ultimately, the figure-eight micro-coil provides a more efficient and consistent site of activation than the circular micro-coil in μMS.

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A review on magnetic and spintronic neurostimulation: challenges and prospects

Saha

Bloom

et al. 2022

Nanotechnology

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In the treatment of neurodegenerative, sensory and cardiovascular diseases, electrical probes and arrays have shown quite a promising success rate. However, despite the outstanding clinical outcomes, their operation is significantly hindered by non-selective control of electric fields. A promising alternative is micromagnetic stimulation (μMS) due to the high permeability of magnetic field through biological tissues. The induced electric field from the time-varying magnetic field generated by magnetic neurostimulators is used to remotely stimulate neighboring neurons. Due to the spatial asymmetry of the induced electric field, high spatial selectivity of neurostimulation has been realized. Herein, some popular choices of magnetic neurostimulators such as microcoils (μcoils) and spintronic nanodevices are reviewed. The neurostimulator features such as power consumption and resolution (aiming at cellular level) are discussed. In addition, the chronic stability and biocompatibility of these implantable neurostimulator are commented in favor of further translation to clinical settings. Furthermore, magnetic nanoparticles (MNPs), as another invaluable neurostimulation material, has emerged in recent years. Thus, in this review we have also included MNPs as a remote neurostimulation solution that overcomes physical limitations of invasive implants. Overall, this review provides peers with the recent development of ultra-low power, cellular-level, spatially selective magnetic neurostimulators of dimensions within micro- to nano-range for treating chronic neurological disorders. At the end of this review, some potential applications of next generation neuro-devices have also been discussed.

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Planar figure-8 coils for ultra-focal and directional micromagnetic brain stimulation

Cited by 7 publications

References 25 publications

Short-pulsed micro-magnetic stimulation of the vagus nerve

Short-pulsed micro-magnetic stimulation of the vagus nerve

Improving focality and consistency in micromagnetic stimulation

A review on magnetic and spintronic neurostimulation: challenges and prospects

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