Background: Traditional repetitive Transcranial Magnetic Stimulation (rTMS) remains applicable in speech studies on healthy participants. Although the procedure of inducing speech arrest by rTMS has been used for over 25 years, there are still significant discrepancies in its methodology.
Objective: The study aimed to simplify and improve the old methodology of triggering speech arrest by (rTMS). Our goal was to establish the best step-by-step algorithm and verify the procedure on a representative group of participants.
Methods: 47 healthy, right-handed volunteers (23 men and 24 women) at a median age of 23 (range 19-34) were included in the study. Handedness was determined using the Edinburgh Handedness Inventory Test. After setting the individual's motor threshold (MT) and heuristic choice of the place of stimulation, which targeted Inferior Frontal Gyrus (IFG), participants were asked to count downwards from 20 to 10. While counting, a series of 2-second pulses was generated at a frequency of 2 Hz at 120% or 150% of MT. The procedure was video-recorded and subsequently assessed by 3 independent reviewers and self-assessed by participants on visual analogue scales for the effect and comfort of stimulation.
Results: Speech arrest was induced in 45 people (95.7%). Language dominance was determined to be either left-sided (for 42.2%) or bilateral (55.3%). Total speech arrest was observed more often in participants for whom Broca's area was active exclusively in the left hemisphere.
Conclusion: In our study, we present the step-by-step procedure for a simplified, as far as possible, methodology of inducing speech arrest using rTMS with its verification on a representative group of right-handed healthy individuals. Our results prove that the chosen stimulation parameters present a good efficacy ratio and seems to be justified. The traditional applications of rTMS in speech studies may be highly broadened if the methods used are further improved and simplified.
Keywords: Repetitive transcranial magnetic stimulation; methodology; speech; speech arrest.