Micromagnetic Stimulation of the Mouse Auditory Cortex In Vivo Using an Implantable Solenoid System

Objective: Recent studies have reported that micromagnetic stimulation (μMS), which can activate neurons and neural networks via submillimeter inductors, may address several limitations of conventional magnetic stimulation methods. Previous studies have examined the effects of μMS on single neurons, yet little is known about how μMS can affect brain tissue including local neural networks. Here, we propose a new, readily available implantable μMS system and computationally and experimentally evaluate its validity. Methods: We conducted numerical calculations and experiments to evaluate the physical characteristics, including magnetic flux density, temperature, coil impedance, and structural integrity of the flexible board supporting the μMS coils. We then compared soundand μMS-driven neural responses in the mouse auditory cortex using flavoprotein autofluorescence imaging. Results: Our system successfully activated neural tissue, and we observed activity propagation in local neural networks on the brain surface beyond restricted activation of single neurons. Examining the relationships between stimulation parameters and response characteristics, we found that stimulation amplitude and pulse width were the two most important parameters to effectively induce neural activity. Conclusion: Our μMS device has sufficient potential to drive the brain as an implantable magnetic stimulator for basic neuroscience and clinical applications, although further investigation is required. Significance: μMS can selectively drive and modulate activity in local neural network even at an in vivo tissue level.