Silicon Spike: An Arduino-based low-cost and open-access triggerbox to precisely control TMS devices.

Transcranial magnetic stimulation (TMS) is a widely used tool in the field of clinical and cognitive neuroscience. To exploit its excellent temporal properties, TMS usually relies on triggerbox devices, which temporize the delivery of magnetic pulses according to the paradigm requirements. However, a main limitation of most of the widely used triggerbox devices is that they rely solely on the experimental computer processor, which might add temporal uncertainty in delivering the TMS pulse when the computer's resources are drained by other experimental devices or by task execution itself, especially during repetitive TMS or dual-coil protocols. We aimed at developing a low-cost and easily reproducible triggerbox device which could overcome these limitations by relying on an external processor to handle the timing precision. We used an Arduino Uno R4 Minima to build Silicon Spike, a low-cost ($60) triggerbox device. We tested the device's precision in delivering the TMS pulses under different working load conditions, and the impact over time. All of the tests were ecological, delivering real TMS pulses during dual-coil, repetitive, and patterned TMS protocols. We obtained extremely high precision (< 0.022 ms) in all of the tests. This means that, for smaller or longer latencies, the error remains negligible for TMS studies. Thus, the Silicon Spike device demonstrated microsecond precision in handling the TMS pulse delivery, establishing itself as a simple and yet precise device. We freely provide the source code and the hardware schematics, allowing anyone to reproduce our work.