Transcranial Magnetic Stimulation (TMS) is a neuromodulation technique that non-invasively depolarizes neurons in the brain. During TMS, a pulse (or multiple pulses) of a time-varying magnetic field (H) is delivered to the brain using specialized coils. The Quadruple Butterfly Coil (QBC) is a novel coil design that shows increased focality of the induced electric field over that of the standard figure-of-eight (FoE) coil. Using 50 different head models created from MRI scans of healthy individuals, our research investigated the role that brain-scalp distance (BSD) plays in the brain's response to the magnetic fields generated by the QBC and FoE. The variability of BSD is an inherent characteristic in the human population. As the BSD increases, so does the distance between the brain and TMS coil. Therefore, the anatomical variation of BSD is an independent variable that may play a significant role in the intensity of the induced electric field produced in the brain. Our results show no significant difference of the QBC's focality to that of the FoE with respect to BSD.

Transcranial magnetic stimulation (TMS) is a noninvasive neuromodulation technique, an FDA-approved treatment method for various neurological disorders such as depressive disorder, Parkinson's disease, post-traumatic stress disorder, and migraine. However, information concerning the molecular/cellular-level mechanisms of neurons under magnetic simulation (MS), particularly at the single neural cell level, is still lacking, resulting in very little knowledge of the effects of MS on neural cells. In this paper, the effects of MS on the behaviors of neural cell N27 at the single-cell level on coverslip glass substrate and anodic aluminum oxide (AAO) nanoporous substrate are reported for the first time. First, it has been found that the MS has a negligible cytotoxic effect on N27 cells. Second, MS decreases nuclear localization of paxillin, a focal adhesion protein that is known to enter the nucleus and modulate transcription. Third, the effect of MS on N27 cells can be clearly observed over 24 h, the duration of one cell cycle, after MS is applied to the cells. The size of cells under MS was found to be statistically smaller than that of cells without MS after one cell cycle. Furthermore, directly monitoring cell division process in the microholders on a chip revealed that the cells under MS generated statistically more daughter cells in one average cell cycle time than those without MS. All these results indicate that MS can affect the behavior of N27 cells, promoting their proliferation and regeneration.

This paper reports the behaviors of neuron cell N27 growth on nanostructured surface and under transcranial magnetic stimulation (TMS) at single cell level for the first time. First, the growth of neuron cell N27 on anodic aluminum oxide (AAO) nanoporous surface has been studied. It has been found the cells show much preference to grow on the nanostructured surface over the flat coverslip glass surface. Second, the sizes of cells grown on AAO nanoporous surface with TMS and without TMS have been studied. It has been found the sizes of cells with TMS are statistically smaller than those without TMS in the same period of time, indicating the TMS might speed up the cell division. To verify this observation, the growth of single N27 cells inside SU8 microholders with and without TMS has been investigated. It has been found that up to 17% more daughter cells can be divided when the cells are subjected to TMS compared to those without TMS. All these results suggest the TMS can contribute to the growth of N27 cells, benefiting the neuron regeneration.

Dual-site Transcranial Magnetic Stimulation (ds-TMS) is a TMS protocol that involves stimulating two areas of the brain in close succession. This method is useful for studying the connections between two physical parts of the brain. TMS coils are generally designed for use on a single target area in the brain. When ds-TMS targets are in close proximity to one another, using traditional coils in a limited space increases the possibility of errors associated with positioning, resulting in inconsistent pulse strength and trajectory. We developed a single TMS coil that uses temporal interference (TI) to stimulate multiple targets within close proximity without compromising the ideal positioning of either location. TI TMS operates based on the frequency difference of two magnetic fields delivered simultaneously. The frequency difference between the two fields results in an envelope which can be steered to target a different location without moving the coil. We designed a TI-TMS coil and show that the peak induced electric field can be steered 4 cm in either direction (8 cm range) from the center point of the coil while delivering a peak field of 120 V/m, which is above the minimum 100 V/m needed to activate neurons. An experimental model was built using the same dimensions as the simulation model and validated that the physical model is able to steer the magnetic pulse using TI.

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