Short interval intracortical inhibition: Variability of amplitude and threshold-tracking measurements with 6 or 10 stimuli per point

Hatice Tankisi,Bülent Cengiz,Gintaute Samusyte,James Howells,Martin Koltzenburg,Hugh Bostock

doi:10.1016/j.neucli.2021.11.006

Abstract

Reduced short-interval intracortical inhibition (SICI) in motor neuron disease has been demonstrated by amplitude changes (A-SICI) and threshold-tracking (T-SICI) using 10 stimuli per inter-stimulus interval (ISI). To test whether fewer stimuli would suffice, A-SICI and T-SICI were recorded twice from 30 healthy subjects using 6 and 10 stimuli per ISI. Using fewer stimuli increased mean A-SICI variances by 23.8% but the 7.3% increase in T-SICI variance was not significant. We conclude that our new parallel threshold-tracking SICI protocol, with 6 stimuli per ISI, can reduce time and stimulus numbers by 40% without appreciable loss of accuracy.

Highlights

The transcranial magnetic stimulation (TMS) technique of short-interval intracortical inhibition (SICI) can be recorded by using constant stimuli, and measuring the effect of the conditioning stimulus on the amplitude of the response to the test stimulus, or by tracking the effect of the conditioning stimulus on the threshold stimulus required to elicit a constant target response
A MagstimÒ D70 figure-of-8 coil was positioned on the contralateral hemisphere, to excite motor evoked potentials (MEPs) of the right first dorsal interosseus (FDI) muscle
For A-SICI, resting motor thresholds were first determined for 200mV (RMT200) and 1 mV (TS1mV) peak-to-peak MEPs, using a ‘4!2!10 tracking rule [8]

Summary

Introduction

The transcranial magnetic stimulation (TMS) technique of short-interval intracortical inhibition (SICI) can be recorded by using constant stimuli, and measuring the effect of the conditioning stimulus on the amplitude of the response to the test stimulus (i.e. amplitude SICI: A-SICI), or by tracking the effect of the conditioning stimulus on the threshold stimulus required to elicit a constant target response (i.e. threshold-tracking SICI: T-SICI). Both methods showed reduced inhibition in patients with motor neuron disease (MND), with high specificity and sensitivity, using 10 stimuli at each of nine inter-stimulus intervals (ISI) from 1 to 7 ms [9]. The TSICI(10) protocol was previously designated T-SICIp2 [8] and distinct from the earlier serial threshold-tracking protocol T-SICIs [4,5,8,10]

Objectives

Methods

Results

Conclusion