Transcranial Magnetic stimulation (TMS) modulates functional activity of SH-SY5Y cells: An in vitro model provides support for assumed excitability changes

Repetitive Transcranial Magnetic Stimulation (rTMS) is an established neuromodulation technique, using electromagnetic pulses that, depending on the precise parameters, are assumed to lead to lasting neural excitability changes. rTMS has widespread applications in both research and therapy, where it has been FDA approved and is considered a first-line treatment for depression, according to recent North American and European guidelines. However, these assumed excitability effects are often difficult to replicate, and highly unreliable on the single subject/patient level. Given the increasing application of rTMS, especially in clinical practice, the absence of a method to unequivocally determine effects of rTMS on human neuronal excitability is problematic. We have taken a first step in addressing this bottleneck, by administering excitatory and inhibitory rTMS protocols, iTBS and cTBS, to a human in vitro neuron model; differentiated SH-SY5Y cells. We use live calcium imaging to assess changes in neural activity following stimulation, through quantifying fluorescence response to chemical depolarization. We found that iTBS and cTBS have opposite effects on fluorescence response; with iTBS increasing and cTBS decreasing response to chemical depolarization. Our results are promising, as they provide a clear demonstration of rTMS after-effects in a living human neuron model. We here present an in-vitro live calcium imaging setup that can be further applied to more complex human neuron models, for developing and evaluating subject/patient-specific brain stimulation protocols.