Abstract
Objective and Impact Statement. There is a need to develop rodent coils capable of targeted brain stimulation for treating neuropsychiatric disorders and understanding brain mechanisms. We describe a novel rodent coil design to improve the focality for targeted stimulations in small rodent brains. Introduction. Transcranial magnetic stimulation (TMS) is becoming increasingly important for treating neuropsychiatric disorders and understanding brain mechanisms. Preclinical studies permit invasive manipulations and are essential for the mechanistic understanding of TMS effects and explorations of therapeutic outcomes in disease models. However, existing TMS tools lack focality for targeted stimulations. Notably, there has been limited fundamental research on developing coils capable of focal stimulation at deep brain regions on small animals like rodents. Methods. In this study, ferromagnetic cores are added to a novel angle-tuned coil design to enhance the coil performance regarding penetration depth and focality. Numerical simulations and experimental electric field measurements were conducted to optimize the coil design. Results. The proposed coil system demonstrated a significantly smaller stimulation spot size and enhanced electric field decay rate in comparison to existing coils. Adding the ferromagnetic core reduces the energy requirements up to 60% for rodent brain stimulation. The simulated results are validated with experimental measurements and demonstration of suprathreshold rodent limb excitation through targeted motor cortex activation. Conclusion. The newly developed coils are suitable tools for focal stimulations of the rodent brain due to their smaller stimulation spot size and improved electric field decay rate.
Highlights
Transcranial magnetic stimulation (TMS) is an FDAapproved treatment for major depression disorder (MDD), migraine, and obsessive-compulsive disorder (OCD) [1–4]
Working together with imaging modalities, such as electroencephalogram (EEG) and functional magnetic resonance imaging, it has been used for mapping stimulation-elicited brain activity [6, 7]
These were done through analytical models or numerical simulations using either the finite element method (FEM) or finite difference method (FDM) [15, 18–22]
Summary
Transcranial magnetic stimulation (TMS) is an FDAapproved treatment for major depression disorder (MDD), migraine, and obsessive-compulsive disorder (OCD) [1–4]. Several previous works have been focused on introducing new coils with improved depth-focality performance and reduced spot size These were done through analytical models or numerical simulations using either the finite element method (FEM) or finite difference method (FDM) [15, 18–22]. There is a strong demand for developing new TMS coil designs capable of stimulating a focal brain region, for smaller animals like rodents. Considering the small penetration depth required for rodents’ brain stimulation, it is unknown how the magnetic core behaves in terms of penetration depthfield focality tradeoff, a critical metric in assessing TMS coils’ performance. The design demonstrated smaller stimulation spot size, improved electric field decay rate, and up to 60% lower energy requirement for rodent brain stimulation. The results were validated with the finite element method (FEM) simulations and experiments
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