Investigating the intrasession reliability of short and long-afferent inhibition.

Abstract

Afferent Inhibition is the reduction in motor output when Transcranial Magnetic Stimulation (TMS) of the motor cortex is preceded by peripheral nerve stimulation. Afferent inhibition can be subdivided into two circuits of Short- (SAI) and Long-Afferent Inhibition (LAI). Reliability reflects the repeatability of a measure and can be measured in terms of both absolute and relative reliability. Relative reliability refers to the ability of a measure to identify individuals on repeated testing, measured through the Intraclass Correlation Coefficient (ICC); absolute reliability is the repeatability of scores through repeated testing, measured through Standard Error of Measurement (SEM) and Smallest Detectable Change (SDC). Current literature has highlighted only the intersession reliability of SAI and LAI, but measures of the intrasession reliability are also needed. This study aims to quantify the intrasession reliability of SAI and LAI, alongside identifying the minimum number of trials needed to obtain a reliable measure. 30 healthy individuals (21.17 ± 2.84 years) took part in one session, with SAI and LAI obtained three times at 30-minute intervals. To identify the minimum number of trials required to reliably elicit SAI and LAI, relative reliability was assessed at running intervals of every 5 trials. Results indicate that SAI had moderate–high, and LAI had high-excellent relative reliability. Both SAI and LAI had high amounts of measurement error. LAI was seen to have high relative reliability when only 5 frames of data were included, whereas for SAI, ~20-30 frames of data resulted in high relative reliability. For LAI, a minimal sample size of 19 is needed to have an SDCGroup < 10, whereas for SAI, a sample size of 22 is needed to achieve the same. These results can be used to inform future work regarding the clinical utility of these measures, particularly in terms of their diagnostic ability.