Abstract
Short-latency afferent inhibition (SAI) and long-latency afferent inhibition (LAI) occur when the motor evoked potential (MEP) elicited by transcranial magnetic stimulation (TMS) is reduced by the delivery of a preceding peripheral nerve stimulus. The intra-individual variability in SAI and LAI is considerable, and the influence of sample demographics (e.g., age and biological sex) and testing context (e.g., time of day) is not clear. There are also no established normative values for these measures, and their reliability varies from study-to-study. To address these issues and facilitate the interpretation of SAI and LAI research, we pooled data from studies published by our lab between 2014 and 2020 and performed several retrospective analyses. Patterns in the depth of inhibition with respect to age, biological sex and time of testing were investigated, and the relative reliability of measurements from studies with repeated baseline SAI and LAI assessments was examined. Normative SAI and LAI values with respect to the mean and standard deviation were also calculated. Our data show no relationship between the depth of inhibition for SAI and LAI with either time of day or age. Further, there was no significant difference in SAI or LAI between males and females. Intra-class correlation coefficients (ICC) for repeated measurements of SAI and LAI ranged from moderate (ICC = 0.526) to strong (ICC = 0.881). The mean value of SAI was 0.71 ± 0.27 and the mean value of LAI was 0.61 ± 0.34. This retrospective study provides normative values, reliability estimates, and an exploration of demographic and testing influences on these measures as assessed in our lab. To further facilitate the interpretation of SAI and LAI data, similar studies should be performed by other labs that use these measures.
Highlights
Afferent inhibition is observed when the motor evoked potential (MEP) elicited by transcranial magnetic brain stimulation (TMS) is supressed by a preceding peripheral nerve stimulus
This suggests that in a healthy control population, short-latency afferent inhibition (SAI) and latency afferent inhibition (LAI) are not expected in all participants
Inter-individual differences in SAI and LAI were not associated with time of day or biological sex
Summary
Afferent inhibition is observed when the motor evoked potential (MEP) elicited by transcranial magnetic brain stimulation (TMS) is supressed by a preceding peripheral nerve stimulus. This phenomenon may be observed when nerve stimuli are delivered at long (200-1000ms) or short (20-25ms) inter-stimulus intervals (ISI) with respect to the subsequent TMS pulse [1,2,3]. Cholinergic activity has been shown to modulate short-latency afferent inhibition (SAI), which is suppressed in cognitive disorders [4,5,6,7]. Short- and long-latency afferent interaction study design, data collection and analysis, decision to publish, or preparation of the manuscript
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