Increasing pulse energy of 5Hz rTMS improves its efficacy in inducing excitatory aftereffects

Introduction High frequency repetitive transcranial magnetic stimulation induces excitation when applied to the motor cortex as reflected by the increase MEP amplitudes after the stimulation. The effects differ according to pulse width, probably due to higher content of energy in the wider pulses and their ability to cause wider activation in comparison to shorter pulse shapes. Here we focus on the aftereffects generated with high frequency controllable pulse TMS (cTMS) with different pulse widths. Objectives To investigate the influence of pulse energy by using different stimulation intensities and pulse widths on the excitatory plastic aftereffects of high frequency (HF) rTMS. Methods Using a controllable pulse stimulator TMS (cTMS), we stimulated the hand motor cortex with 5 Hz rTMS applying 1200 bidirectional pulses with the main component widths of 80, 100 and 120 microseconds. 14 healthy subjects were initially investigated for six randomized sessions first with 80% RMT for anterior-posterior (AP) and posterior-anterior (PA). Then three more sessions using same pulse widths were added for 90% RMT anterior-posterior (AP). Results 80% HF rTMS did not produce any significant excitation in either AP or PA direction. 90% RMT AP stimulation with 100 and 120 microsecond-wide pulses were more excitatory, when compared to the 80 microsecond-wide pulses. We also found a correlation between the individual pulse energy and the plastic outcome of each session. Conclusions HF rTMS with wider pulses is more effective in producing excitatory aftereffects, an effect that correlated with the higher energy content of wider pulses and higher intensity. Significance The findings here suggest that wider pulses are capable of inducing more excitation, a fact that could contribute to better results in future clinical studies performed with wider pulses.