Performance Characterization of an Actively Cooled Repetitive Transcranial Magnetic Stimulation Coil for the Rat

Parthoens, Joke; Verhaeghe, Jeroen; Servaes, Stijn; Miranda, Alan; Stroobants, Sigrid; Staelens, Steven

doi:10.1111/ner.12387

Cited by 38 publications

(32 citation statements)

References 30 publications

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“…This is in contrast to the induced electric field produced with a commercial butterfly coil, which resulted in a greater peak electric field (224 V/m) and more widespread electric field such that the electric field was >150 V/m at a depth of 10 mm from the surface of the brain and encapsulated the entire brain. This is similar to the electric field modeling with the commercial Cool-40 Rat coil, which induces a peak electric field of 220 V/m with a penetration of ≥50 V/m at a depth of ~10 mm ( Parthoens et al, 2016 ). These results suggest that although our coils produce weaker electric fields, they induce more focal stimulation.…”

Section: Discussionsupporting

confidence: 74%

“…Offsetting coil position can achieve greater stimulation focality ( Rotenberg et al, 2010 ; Vahabzadeh-Hagh et al, 2011 ); however, an alternative approach for rodent TMS is to scale-down coil size to improve focality. Whilst recent work has shown that coil size can be dramatically reduced and maintain high intensity capabilities, it still results in relatively unfocal stimulation ( Parthoens et al, 2016 ). In contrast, compromising stimulation intensity for greater focality, rodent-specific coils (circular, 8 mm outer diameter, ~12 mT; Figure 1B ) have recently been shown to induce structural and molecular plasticity in midbrain and cortical brain regions of mice ( Rodger et al, 2012 ; Makowiecki et al, 2014 ).…”

Section: Introductionmentioning

confidence: 99%

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Construction and Evaluation of Rodent-Specific rTMS Coils

Tang

Lowe

Garrett

et al. 2016

Front. Neural Circuits

110

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Rodent models of transcranial magnetic stimulation (TMS) play a crucial role in aiding the understanding of the cellular and molecular mechanisms underlying TMS induced plasticity. Rodent-specific TMS have previously been used to deliver focal stimulation at the cost of stimulus intensity (12 mT). Here we describe two novel TMS coils designed to deliver repetitive TMS (rTMS) at greater stimulation intensities whilst maintaining spatial resolution. Two circular coils (8 mm outer diameter) were constructed with either an air or pure iron-core. Peak magnetic field strength for the air and iron-cores were 90 and 120 mT, respectively, with the iron-core coil exhibiting less focality. Coil temperature and magnetic field stability for the two coils undergoing rTMS, were similar at 1 Hz but varied at 10 Hz. Finite element modeling of 10 Hz rTMS with the iron-core in a simplified rat brain model suggests a peak electric field of 85 and 12.7 V/m, within the skull and the brain, respectively. Delivering 10 Hz rTMS to the motor cortex of anaesthetized rats with the iron-core coil significantly increased motor evoked potential amplitudes immediately after stimulation (n = 4). Our results suggest these novel coils generate modest magnetic and electric fields, capable of altering cortical excitability and provide an alternative method to investigate the mechanisms underlying rTMS-induced plasticity in an experimental setting.

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Section: Discussionsupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

Construction and Evaluation of Rodent-Specific rTMS Coils

Tang

Lowe

Garrett

et al. 2016

Front. Neural Circuits

110

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show abstract

“…. In another rat study, at 10 mm depth the induced electrical field strength decreased to 25% of that on the brain surface 26 . Interestingly, the half power region (HPR) was as broad as ~7 x 7 mm (0.51 cm Although concrete numbers were not provided for the 70 mm figure-8 coil, Salvador and Miranda commented that the HPR for the 70 mm coil was larger than that of the 25 mm coil.…”

mentioning

confidence: 89%

Repetitive Transcranial Magnetic Stimulation to the Unilateral Hemisphere of Rat Brain

Beom

Lee

Paeng

et al. 2016

JoVE

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Previous rodent models of repetitive transcranial magnetic stimulation (rTMS) adopted whole-brain stimulation instead of unilateral hemispheric rTMS, which is unlike the protocols used for human subjects. We report a successful application of rTMS to the unilateral hemisphere of rat brain. The rTMS was delivered with a low-frequency (1 Hz), high-frequency (20 Hz), or sham stimulation protocol to one side of the brain by using a small 25-mm figure-8 coil. We placed the center of the coil 1 cm lateral to the vertex on the biauricular line and angulated the coil 45° to the ground to minimize a potential direct effect of rTMS on the contralateral cortex. We also used an in-house water cooling system to enable repetitive magnetic stimulation for more than 20 min, even at a 20-Hz stimulation frequency. Increases in the transcriptions of immediate early genes (Arc, Junb, and Egr2) were greater after rTMS than after sham stimulation. After 5 consecutive days of 20-min 1-Hz rTMS, bdnf mRNA expression was significantly higher in stimulated cortex than in contralateral side. The model presented herein will elucidate the molecular mechanisms of rTMS by allowing analysis of the inter-hemispheric difference in its effect.

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“…Here we overcame this problem by interpreting the centrally fitted sphere as the global spherical approximation of the head, as it nicely covered the whole brain, and was in size similar to, e.g., the spherical model used in Ref. 23 . We computed the E-field in the spherical model with the analytical closed-form solution 36 .…”

Section: Methodsmentioning

confidence: 99%

Individual head models for estimating the TMS-induced electric field in rat brain

Koponen

Stenroos

Nieminen

et al. 2020

Sci Rep

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In transcranial magnetic stimulation (TMS), the initial cortical activation due to stimulation is determined by the state of the brain and the magnitude, waveform, and direction of the induced electric field (E-field) in the cortex. The E-field distribution depends on the conductivity geometry of the head. The effects of deviations from a spherically symmetric conductivity profile have been studied in detail in humans. In small mammals, such as rats, these effects are more pronounced due to their less spherical head, proportionally much thicker neck region, and overall much smaller size compared to the TMS coils. In this study, we describe a simple method for building individual realistically shaped head models for rats from high-resolution X-ray tomography images. We computed the TMS-induced E-field with the boundary element method and assessed the effect of head-model simplifications on the estimated E-field. The deviations from spherical symmetry have large, non-trivial effects on the E-field distribution: for some coil orientations, the strongest stimulation is in the brainstem even when the coil is over the motor cortex. With modelling prior to an experiment, such problematic coil orientations can be avoided for more accurate targeting.

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Performance Characterization of an Actively Cooled Repetitive Transcranial Magnetic Stimulation Coil for the Rat

Cited by 38 publications

References 30 publications

Construction and Evaluation of Rodent-Specific rTMS Coils

Construction and Evaluation of Rodent-Specific rTMS Coils

Repetitive Transcranial Magnetic Stimulation to the Unilateral Hemisphere of Rat Brain

Individual head models for estimating the TMS-induced electric field in rat brain

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