Characterizing the corticomotor connectivity of the bilateral ankle muscles during rest and isometric contraction in healthy adults

Abstract

The investigation of the corticomotor connectivity (CMC) to leg muscles is an emerging research area, and establishing reliability of measures is critical. This study examined the measurement reliability and the differences between bilateral soleus (SOL) and tibialis anterior (TA) CMC in 21 neurologically intact adults. Using single pulse transcranial magnetic stimulation (TMS), each muscle's CMC was assessed twice (7 ± 2 days apart) during rest and active conditions. CMC was quantified using a standardized battery of eight measures (4/condition): motor threshold during resting (RMT), motor evoked potential amplitude and latency (raw and normalized to height) in both conditions, contralateral silent period (CSP) during active. Using two reliability metrics (intraclass correlation coefficient and coefficient of variation of method error; good reliability: ≥0.75 and ≤15, respectively) and repeated-measures ANOVA, we investigated the reliability and Muscle X Body Side interaction. For both muscles, RMT, resting raw and normalized latencies, and active raw latency demonstrated good reliability, while CSP had good reliability only for TA. Amplitude did not demonstrate good reliability for both muscles. SOL CMC was significantly different from TA CMC for all measures but CSP; body side had no significant effect. Therefore, only certain measures may reliably quantify SOL and TA CMC while different CMC (except CSP) between SOL and TA suggests dissimilar corticospinal drive to each muscle regardless of the side.

Single Sessions of High-Definition Transcranial Direct Current Stimulation Do Not Alter Lower Extremity Biomechanical or Corticomotor Response Variables Post-stroke

“…Another area that needs further investigation is the relevance of studying MEP amplitude versus latency. MEP latency seems to be a much more stable parameter in healthy and post-stroke individuals (Charalambous et al, 2018). This was also seen in our sample, as there was less variability in latency in the paretic and non-paretic lower extremities compared to amplitude.…”

“…The TMS assessment was performed using a double-cone coil and a Magstim BiStim2 stimulator (Magstim, Inc., Whitland, United Kingdom). Hotspot identification was guided by neuronavigation (Brainsight, Rogue Research, Montreal, QC, Canada) (Charalambous et al, 2018). Briefly, hotspots were identified using a single suprathreshold single TMS pulse applied over a 3x5 grid transposed over an average Montreal Neurological Institute MRI brain image.…”

“…Data were imported into MATLAB and demeaned using the average signal of the first and last 0.05 s. MEP amplitude was then calculated as the difference between the maximum and minimum values in a 0.08 s window starting at 0.025 s. Once amplitude was calculated the signal was rectified and the time from the TMS trigger pulse to the start of the MEP, i.e., latency, was measured. MEP latency was defined as the point when the rectified MEP signal amplitude was greater than the mean plus three standard deviations of the signal amplitude occurring 0.08 s before the TMS trigger pulse (Cacchio et al, 2011; Charalambous et al, 2018) for at least 0.001 s. Latency was then normalized to participant height and is reported as ms/m. Once all MEP metrics were calculated the data were exported and visually inspected to ensure the accuracy and validity of the values.…”

Bilateral Assessment of the Corticospinal Pathways of the Ankle Muscles Using Navigated Transcranial Magnetic Stimulation

“…In humans, the functional state of this tract (corticomotor response - CMR) can be feasibly assessed using transcranial magnetic stimulation (TMS), a non-invasive brain stimulation tool 9,10 . Since the introduction of TMS and given their functional significance during upright postural task and walking, CMR of TA and SOL have been assessed in various cohorts and tasks 11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32…”

“…Finally, representative data will be presented and discussed. The protocol described here is derived from that in Charalambous et al 2018 32 .…”