Normative Values for Intertrial Variability of Motor Responses to Nerve Root and Transcranial Stimulation: A Condition for Follow-Up Studies in Individual Subjects

Abstract

ObjectiveIntertrial variability (ITV) of motor responses to peripheral (CMAP) and transcranial (MEP) stimulation prevents their use in follow-up studies. Our purpose was to develop strategies to reduce and measure CMAP and MEP ITV to guide long-term monitoring of conduction slowing and conduction failure of peripheral and central motor pathway in the individual patient.MethodsMaximal compound muscle action potentials to High Voltage Electrical Stimulation (HVES) of lumbo-sacral nerve roots (r-CMAP) and activated, averaged motor evoked potentials (MEPs) to Transcranial Magnetic Stimulation (TMS) using double cone coil were recorded from 10 proximal and distal muscle districts of lower limbs. The procedure was repeated twice, 1–2 days apart, in 30 subjects, including healthy volunteers and clinically stable multiple sclerosis patients, using constant stimulating and recording sites and adopting a standardized procedure of voluntary activation. ITV for latency and area indexes and for the ratio between MEP and r-CMAP areas (a-Ratio) was expressed as Relative Intertrial Variation (RIV, 5th-95th percentile). As an inverse correlation between the size of area and ITV was found, raw ITV values were normalized as a function of area to make them comparable with one another.ResultsAll RIV values for latencies were significantly below the optimum threshold of ± 10%, with the exception of r-CMAP latencies recorded from Vastus Lateralis muscle. RIVs for a-Ratio, the most important index of central conduction failure, ranged from a maximum of -25.3% to +32.2% (Vastus Medialis) to a minimum of -15.0% to + 17.4% (Flexor Hallucis Brevis).ConclusionsThe described procedure represents an effort to lower as much as possible variability of motor responses in serial recording; the reported ITV normative values are the necessary premise to detect significant changes of motor conduction slowing and failure in the individual patient in follow-up studies.

Intra and inter-session reliability of rapid Transcranial Magnetic Stimulation stimulus-response curves of tibialis anterior muscle in healthy older adults

“…This study assessed the reliability of TMS-related measures collected from the TA muscle at rest and at 5%MVC of a population of 24 healthy older adults (mean age of 62 years). These measures, although acquired with the rapid protocol for SR curves proposed in [ 9 ], were similar, in terms of magnitude, to those previously obtained on the TA muscle of healthy subjects [ 6 , 18 , 29 , 30 , 47 ]. Comparisons were not possible for the AURC and I50, since no previous studies evaluated this outcome on the TA muscle.…”

“…Compared to absolute reliability, relative reliability was more commonly investigated in the literature. Several studies have estimated ICC values for TMS outcomes in TA muscle on healthy subjects [ 6 , 18 , 29 , 30 , 47 ]. Good relative reliability (ICC>0.70) was generally found for resting MT, slope, latency, silent period, and MEP amplitude; only one study [ 30 ] observed a moderate reliability for latency (ICC of 0.55–0.71 during isometric muscle contractions of 10% to 60%MVC) and silent period (ICC of 0.16–0.40).…”

Influence of Breathing and Chewing on Timing of Flavor Detection

“…That is, time lag between flavor detection in the brain and time of signaling by the hand might have affected the determination of the respiratory phase wherein detection signals occurred. A recent study reports that transcranial magnetic stimulation of the motor area can evoke potentials in the flexor hallucis brevis and that the average latency period for evoked potentials is less than 40 msec [13]. In this study, the average latency was 1.2% of the average time of the average respiratory cycle, including the pausing phase (Figure 2(b)).…”

Neurophysiological Changes in the First Year After Cell Transplantation in Sub-acute Complete Paraplegia

“…Latencies and peak-to-peak amplitudes were quantified and replicates averaged. All recording electrode localizations were measured from landmarks, detail marked in ink, and photographed for accurate replication in subsequent sessions ( 73 ).…”