Frequency-Dependent Effects of Transcranial and Translumbosacral Magnetic Stimulation on Anorectal Neurophysiology: A Dose-Response Study in Healthy Women.

INTRODUCTION

We recently showed that prolonged anorectal motor-evoked potential (MEP) latencies are associated with impaired anorectal function in women with fecal incontinence. Repetitive transcranial magnetic stimulation (rTMS) and translumbosacral magnetic stimulation (rTLSMS) are emerging neuromodulatory treatments, yet optimal frequency and site parameters remain undefined. This study evaluated the acute neurophysiological effects of rTMS and rTLSMS in healthy volunteers.

METHODS

In a randomized crossover study, ten healthy women (18-35 years) underwent TMS and TLSMS assessments measuring MEP latencies/amplitudes in anal and rectal muscles across 10 neural segments. Stimulation was delivered in randomized sessions: rTMS at 1 and 5 Hz (250 pulses) and rTLSMS at 1, 5, and 10 Hz (2,400 pulses).

RESULTS

Five-Hz rTMS significantly reduced latencies in five segments and increased amplitudes in five. In contrast, 1 Hz rTMS had no effect. For rTLSMS, 5 Hz reduced latency in two segments and increased amplitude in two segments, while no significant changes were observed in the remaining segments. Similarly, 10 Hz reduced latency in one sacro-anal pathway, with no significant effects in other segments. Effect sizes supported 5 Hz stimulation (latency: Cohen's d = -0.24; amplitude: 5 Hz rTLSMS, d = 0.34).

CONCLUSION

Among the tested protocols, 5 Hz stimulation, particularly cortical rTMS, showed the most consistent effects, with significant latency reductions observed in multiple anorectal segments. This frequency-dependent, exploratory study provides a mechanistic basis for further investigation in clinical populations.