A Comparison of Two Methods in Acquiring Stimulus–Response Curves with Transcranial Magnetic Stimulation

Alan J Pearce, Ross Clark, Dawson Kidgell

Research output: Contribution to conferenceAbstract


INTRODUCTION: Transcranial magnetic stimulation (TMS) Stimulus-response (S-R) curves are constructed by plotting the motor evoked potential (MEP) output against the stimulus intensity. S-R curves allow investigators to determine parameters in participants such as motor threshold (MT) and maximal MEP amplitude (MEPmax). S-R curves are used ubiquitously in many different TMS study protocols, however few studies have investigated the methodology of the S-R curve itself; in particular whether properties of the S-R curve differ when investigators use either a "ramped" method starting from a low stimulus intensity and increasing intensity of 5% steps of stimulator output (i.e. 35%, 40%, 45% etc) or a "randomised" method with no particular order in the delivery of stimuli intensity (i.e. 55%, 40%, 85% etc). AIM: This study compared S-R MEP and SP duration response curves to TMS, using to either a ramped or randomised methodology in a hand and arm muscle of both limbs. METHODS: Ten healthy males and females (mean ± SD, age 29.6 ± 6.4 years, 3 female), free of neurological condition, completed two separate testing sessions for the first dorsal interosseous (FDI) and biceps brachii (BB) muscles of both limbs. In one session participants completed, in randomised order, a ramped S-R curve and a randomised curve in left and right FDI muscles. In the other session, participants returned and completed S-R curves, in randomised order, for the BB muscle. Testing between hands and arms were randomised between participants. Both MEP amplitudes and SP durations were plotted against TMS intensity and calculated via a fitted non-linear Boltzman sigmoid equation. MEP amplitude and SP duration were also correlated between S-R curve methods for homologous muscles. RESULTS: No differences were observed in MEP MT or MEPmax amplitude, and SP duration thresholds and maximal durations between ramped or randomised S-R curves of homologous muscles (P>0.05). Statistically significant correlations were observed between MEP amplitudes and SP durations at similar stimulus intensities between ramped or randomised S-R curves for homologous muscles (r=0.78 to 0.97; P<0.01). CONCLUSION: This study has demonstrated that investigators can use either a ramped or randomised S-R curve protocol without the concern of creating “serial order” effects that may affect MEP amplitude or SP duration.
Original languageEnglish
Number of pages1
Publication statusPublished - 19 Jul 2012
Externally publishedYes
EventCongress of the International Society of Electrophysiology and Kinesiology 2012 - Queensland University of Technology, Brisbane, Australia
Duration: 19 Jul 201221 Jul 2012
Conference number: XIXth


ConferenceCongress of the International Society of Electrophysiology and Kinesiology 2012
Abbreviated titleISEK2012

Cite this