Attach the coil that will induce the PA current in the brain to the CTMS stimulator. Set the pulse type to monophasic positive, the pulse width to 120 microseconds, and M ratio to 0.2. Finally, set the stimulus intensity to the one millivolt threshold.
After setting the peripheral electrical stimulus intensity, launch the sensory motor task software routine on a personal computer or PC1. Next, set the interstimulus interval between the peripheral electrical and TMS stimuli to 21 milliseconds. Position the TMS coil over the first dorsal interosseous, or FDI, motor hotspot and ask the participant to hold a slight contraction of the FDI muscle.
Keep the desired number of unconditioned and conditioned trials between eight and 24 stimuli per condition. Run the sensory motor task software routine to control the sensory motor task and send the behavior locked digital triggers to the peripheral and CTMS stimulators. Repeat the procedure for the AP30 current configuration using the coil that induces AP current in the brain.
The average effect of the peripheral electrical conditioning stimulus is to suppress the corticospinal output elicited by the TMS stimulus as shown by the smaller raw, average, peak-to-peak MEP amplitudes in the conditioned MEPs compared to the unconditioned MEPs and short-latency afferent inhibition, or SAI, ratios of less than one. The longer MEP onset latency for the AP30 SAI reflects the longer latency of the input to the corticospinal neuron. In differential effects, the PA120 SAI was similarly enhanced for an index finger response regardless of whether the participant was queued to the index finger or required to remap their response to the index finger following an invalid queue to a non-index finger.
In contrast the AP30 SAI appears to be differentially modulated based on whether the invalid queue required a remap away or toward the index finger.
