Paired-Pulse TMS Comparison of pulse waveforms.
The responses to single and paired-pulse TMS stimulation has been shown to be dependent on the pulse waveform (Sommer et al, 2006), which will differ slightly between manufacturers. As new models enter the market it is important to examine their efficacy, to assess the comparability of trials and clinical interventions performed with different apparatus.
Pulses were recorded using Deymed DuoMAG and Magstim 2002/Bistim stimulators with figure of eight coils. Amplitude and pulse-width were measured for both stimulators at 100%, 75%, 50% and 25% of maximum output for both single and paired pulse stimulation modes. 12 young healthy subjects were tested using single and paired-pulse stimulation to the FDI representation of the motor cortex of the dominant hemisphere. EMG was recorded from the FDI muscle on the contralateral limb. Motor Thresholds were recorded at rest (RMT) and with 10% of maximal active contraction (AMT). Input-output curves were recorded at 90%, 110%, 130% and 150% of RMT. The onset of MEP latency was recorded at 110% of AMT and the duration of cortical silent period at 150% AMT. Paired-pulse TMS stimulation was performed at a interstimulus interval of 2.5ms to measure Short Intracortical Inhibition (SICI). Conditioning stimulus intensity was set at 70%, 80% and 90% AMT in combination with a 1mV test stimulus in sequential recordings to create a SICI input-output curve.
Despite subtle differences in peak pulse amplitude and pulse-width between the two devices, these results suggest that the DuoMAG and Magstim 2002 stimulators produce comparable measurements of common markers of corticospinal excitability and intra-cortical inhibition. For full poster download Deymed MP-Dual and Magstim BiStim comparison.
Duncan Austin, Ricci Hannah,Paul Hammond & John C Rothwell
UCL Institute of Neurology, UK