The Elevate TMS devices enable rectangular pulse shapes, which can be monophasic or biphasic with a variable pulse width to be altered. One experiment applied rTMS at 10 Hz for 16 minutes with four different pulse shapes to the motor cortex (Goetz et al., 2016).  Here, all monophasic pulse shapes but not a biphasic pulse shape produced lasting inhibitory effects on MEP amplitude (Goetz et al., 2016).  The most successful pulse at producing offline effects was a semi-monophasic pulse with an induced current travelling in the posterior-anterior (PA) direction (Goetz et al., 2016). This evidence suggests that a biphasic pulse may not be optimal for producing a lasting effect on cortical excitability.  A different experiment looked at how changing the pulse width whilst keeping pulse frequency constant influenced the offline effect of rTMS on cortical excitability (Halawa et al., 2019). Here, the pulse was monophasic but the pulse width was either 40 μs, 80 μs or 120 μs whilst 900 pulses were delivered at 1 Hz. Here, the pulse width was found to impact the direction and the magnitude of the offline effect on MEP amplitude. When a longer pulse width (120 μs) was used, MEP amplitude increased. However, when shorter pulse widths (40 μs or 80 μs) were used an inhibitory effect was present. Taken together, it appears that the presence of an inhibitory or excitatory effect depends on the pulse width but the magnitude of the overall effect is determined by pulse, with monophasic pulses with induced current travelling in the AP direction appearing to be optimal.

The effect of pulse shape and pulse width also affects the latency and amplitude of the motor threshold, suggesting that different neural populations might be affected depending on the shape of the magnetic pulse. Increasing the pulse width appears to reduce MEP latency with AP currents (D’Ostilio et al., 2016; Halawa et al., 2019) whereas reducing the amplitude of the second phase of the biphasic pulse (making it ‘more monophasic’) reduces the motor threshold (Sommer et al., 2018). Reducing the amplitude of the first phase of a biphasic pulse also appears to change the latency of the MEP (Halawa et al., 2019; Sommer et al., 2018). Such changes in MEP amplitude suggest that different populations of neurons could be selectively targeted by changing TMS pulse parameters (Halawa et al., 2019; Sommer et al., 2018), which can refine rTMS and single pulse protocols by going beyond the conventional biphasic sinusoidal waveform in TMS research.