Towards an improved understanding of the mechanisms underlying magnetic activation of neurons - coil-based magnetic stimulation offers several significant advantages over conventional electric…

The National Institute of Neurological Disorders and Stroke awarded The General Hospital Corporation (Massachusetts General Hospital) $629,733 on August 15, 2026, under the Extramural Research Programs in the Neurosciences and Neurological Disorders program (CFDA 93.853) to support research into the mechanisms of magnetic activation of neurons.

The research combines engineering, electrophysiological recordings, and computational modeling to systematically study how induced electromagnetic fields activate individual neurons. The work addresses fundamental biophysical questions about magnetic stimulation—specifically, the roles of field strength, longitudinal gradient, transverse gradient, and intracellular induction in neuronal activation. The project builds on the advantages of coil-based magnetic stimulation over conventional electrical stimulation, including enhanced spatial precision and reduced adverse tissue reactions, with applications in transcranial magnetic stimulation (TMS) for clinical use and smaller coils for next-generation neural implants such as visual and cochlear prostheses. The research team has developed small coils ranging from 0.1 to 10.0 millimeters in diameter integrated into a physiology rig that captures neuronal responses. Addressing the current limitation that only 30–40 percent of TMS users realize long-term benefits, the work aims to improve the efficacy and reliability of magnetic stimulation for both clinical and implantable applications.

Performance occurs in Boston, Massachusetts, with a period of performance from August 15, 2026, through May 31, 2031.

Towards an improved understanding of the mechanisms underlying magnetic activation of neurons - coil-based magnetic stimulation offers several significant advantages over conventional electric stimulation, including enhanced spatial precision, reduced adverse reactions with surrounding tissue, improved long-term stability. Inductive activation also provides unimpeded penetration through biological tissues. These benefits are leveraged in clinical applications using large external coils, such as transcranial magnetic stimulation (TMS) as well as in translational research (with smaller coils) for next- generation neural implants, such as visual and cochlear prostheses. While TMS can be quite effective, only about 30-40% of TMS users realize long-term benefits. Analogously, for coil-based implants, there are still many fundamental design issues impeding progress. To improve the efficacy and reliability of magnetic stimulation, considerable theoretical and experimental effort has been dedicated to elucidating the underlying mechanisms. However, some of the unique characteristics of induced electromagnetic fields- such as the absence of a scalar potential and their non-conservative nature-have limited progress, leaving critical questions unanswered about the specific biophysical features that mediate magnetic activation. Here, we have combined advances in engineering, electrophysiological, recordings and computational modeling to enable systematic study of these mechanisms. We have developed a series of small coils (0.1 - 10.0 MM diameter) and integrated them into a physiology RIG that enables responses from individual neurons to be captured. Four components of the induced electromagnetic field have previously been suggested to play a role in magnetic stimulation (as a result of theoretical and/or computational studies): field strength, longitudinal gradient, transverse gradient, and intracellular induction. Some of these are also known to drive electric stimulation. For stimuli that are effective in our experiments, i.e., those that elicit spikes in the targeted neuron, we will use computational models to precisely quantify the corresponding levels of each component, and use correlation analysis across many experiments to determine which components play the most important roles in activation. Building on these single-cell insights, additional aims will focus on circuit-level responses, e.g., measurements of how magnetic stimulation shapes synaptic transmission, how the balance between excitation and inhibition is altered, and whether certain postsynaptic response motifs can be reliably generated. These physiologically validated insights will provide a pipeline that feeds parameters into a multiscale predictive model, which will be used to investigate large-scale responses (to both TMS and implanted coils). Together, these studies will provide a comprehensive framework linking coil design and field components to neuronal and network responses for both implantable micro-coils and TMS-relevant coils, providing actionable guidelines to optimize coil configuration and stimulation protocols.