A comparative study to assess synchronisation methods for combined simultaneous EEG and TMS acquisition

Electroencephalography (EEG) combined with transcranial magnetic stimulation (TMS) provides valuable insights into cortical excitability and connectivity but faces challenges including data artefacts, limited spatial resolution, and the need for standardised synchronisation protocols. This study evaluates three TMS-EEG synchronisation paradigms using the Lab Streaming Layer (LSL) to analyse time intervals and latency. Paradigm 1 employs a software-based approach with simultaneous pulses to both EEG and TMS devices. Paradigm 2, another software-based method, transmits a pulse to the TMS device first, followed by the EEG amplifier. Paradigm 3 uses a hardware-based approach where pulses generated by the TMS device are directly routed to the EEG amplifier. Synchronisation was assessed at frequencies of 1, 5, 10, and 20 Hz, with each frequency tested ten times using 100-pulse trains. Results demonstrate that Paradigm 3 provides superior performance, showing narrower distributions, lower time interval error (TIE) and latency values, and higher precision and accuracy. However, it requires a high sample rate from the EEG amplifier and limits additional device integration. Paradigms 1 and 2, while exhibiting greater variability and lower precision, allow for additional device integration and inter-pulse control via LSL. All paradigms achieved low latency and timing error values within acceptable limits for EEG applications, affirming their viability. The choice of synchronisation paradigm has a significant impact on performance, and the current lack of standardisation in TMS-EEG studies presents ongoing challenges. These findings underscore the necessity of selecting an appropriate synchronisation method based on specific study requirements and resources, potentially advancing standardised protocols for TMS and enhancing the reliability of TMS-EEG research.