Accurate and precise digital real-time control of transcranial magnetic stimulation

Abstract Accurate and precise timing of transcranial magnetic stimulation (TMS) is essential for brain-state-dependent and closed-loop algorithms, typically performed based on electroencephalography (EEG) or electromyography (EMG) data. Current TMS devices allow controlling stimulation in real time by using an input trigger signal to time the pulse. Many TMS devices also support using a digital communication protocol to set other aspects of the pulse, such as its waveform, before triggering. However, decoupling the pulse parameters and timing is needlessly complex and results in communication overhead. Furthermore, it is unconventional to combine discrete-time digital communication with a continuous-time trigger signal in digital devices. Using a trigger signal also requires precise timing from the trigger-generating device. Moreover, to accurately time the pulse relative to an external signal, such as the EEG or EMG, the overall delay in the signal pathway needs to be estimated and compensated for. Even then, jitter in the delay causes imprecision in pulse timing. We present an event-based design for a TMS device and a digital communication protocol to control the device without using an input trigger signal. Our design allows timing the stimulation pulses accurately and precisely relative to each other and an external signal, regardless of the delays in the signal pathway. In our design, the TMS device receives and carries out events, while measuring the time since the beginning of a treatment session or an experiment. Each event includes the desired time of execution. When the time is reached, the TMS device carries out the event, if other conditions, such as safety rules, are met. At zero time, the TMS device generates a trigger pulse to synchronize with other devices, such as the EEG. The presented design is a move towards fully digital communication with TMS devices, while improving the timing properties of current TMS device designs. Research Category and Technology and Methods Basic Research: 10. Transcranial Magnetic Stimulation (TMS) Keywords: real-time, event-based, digital, control