Reliability of Transcallosal Inhibition in Healthy Adults

Abstract

Transcallosal inhibition (TCI), assessed using transcranial magnetic stimulation, can provide insight into the neurophysiology of aging and of neurological disorders such as stroke. However, the reliability of TCI using the ipsilateral silent period (iSP) has not been formally assessed, despite its use in longitudinal studies. This study aimed to determine the reliability of iSP onset latency, duration and depth in healthy young and older adults. A sample of 18 younger (mean age 27.7 years, range: 19–42) and 13 older healthy adults (mean age 68.1 years, range: 58–79) attended four sessions whereby the iSP was measured from the first dorsal interosseous (FDI) muscle of each hand. 20 single pulse stimuli were delivered to each primary motor cortex at 80% maximum stimulator output while the participant maintained an isometric contraction of the ipsilateral FDI. The average onset latency, duration of the iSP, and depth of inhibition relative to baseline electromyography activity was calculated for each hand in each session. Intraclass correlation coefficients (ICCs) were calculated for all four sessions, or the first two sessions only. For iSP onset latency the reliability ranged from poor to good. For iSP duration there was moderate to good reliability (ICC > 0.6). Depth of inhibition demonstrated variation in reproducibility depending on which hand was assessed and whether two or four sessions were compared. Bland and Altman analyses showed wide limits of agreement between the first two sessions, particularly for iSP depth. However, there was no systematic pattern to the variability. These results indicate that although iSP duration is reliable in healthy adults, changes in longitudinal studies should be interpreted with caution, particularly for iSP depth. Future studies are needed to determine reliability in clinical populations.

Influences of 12-Week Physical Activity Interventions on TMS Measures of Cortical Network Inhibition and Upper Extremity Motor Performance in Older Adults—A Feasibility Study

“…For iSP, the left FDI muscle was contracted via pinch grip at 25% maximal voluntary contraction (MVC) measured by pinch grip dynamometer and a stimulator output equivalent to 150% RMT was delivered to the left FDI hotspot. Recent work by Fleming and Newham ( 2017 ) has shown that these stimulation parameters are reliable in older adults. The highest acceptable RMT for participation in the current study was 66% of MSO.…”

“…The iSP is a complicated measurement that involves a number of cortical and descending spinal inhibitory connections. The silent period onset is typically ~38 ms after stimulation and can last anywhere from 10 to 70 ms depending on stimulation and level of muscle contraction (Giovannelli et al, 2009 ; Petitjean and Ko, 2013 ; Fleming and Newham, 2017 ; Kuo et al, 2017 ). The ipsilateral inhibition seen in the most commonly measured muscle, the first dorsal interosseous (FDI), certainly involves primary motor cortex (M1) callosal transfer, as degradation of the corpus callosum diminishes the measure (Meyer et al, 1995 ; Li et al, 2013 ).…”

Changes in cortical motor outputs after a motor relapse of multiple sclerosis

“…15 A good reliability has been demonstrated for iSP duration . 18 Furthermore, no effects of varying the magnitude of the contraction have been found on the time course of the iSP or on the depth of inhibition but only when expressed as a percentage of the baseline EMG level. 19 To reduce inter-subject and inter-session variability related to the degree of pre-stimulus contraction, iSP area was normalized for the rectified baseline EMG activity between –50 ms and –20 ms pre-stimulus as follows: …”

Modulation of Interhemispheric Inhibition between Primary Motor Cortices Induced by Manual Motor Imitation: A Transcranial Magnetic Stimulation Study

“…The iSP onset was defined as the time point at which EMG fell below 75% of the mean pre-stimulus EMG for more than 5 ms in the time window of 30–60 ms after the stimulus [ 68 ]. The offset of iSP was defined as the point at which the EMG returned more than 75% of the mean pre-stimulus EMG [ 69 , 70 ]. Trials without observable iSP (at least 25% of EMG suppression lasting less than 10 ms) were excluded before averaging the EMG activity for further analysis.…”