Reproducible Measurement of Human Motoneuron Excitability With Magnetic Stimulation of the Corticospinal Tract

2009 ◽  
Vol 102 (1) ◽  
pp. 606-613 ◽  
Author(s):  
Peter G. Martin ◽  
Anna L. Hudson ◽  
Simon C. Gandevia ◽  
Janet L. Taylor
Keyword(s):  
Magnetic Stimulation ◽  
Corticospinal Tract ◽  
Motor Evoked Potentials ◽  
Compound Action Potential ◽  
Maximal Response ◽  
Response Curves ◽  
Stimulus Response ◽  
Maximal Output ◽  
Voluntary Contractions ◽  
Stimulation Of

It is difficult to test responses of human motoneurons in a controlled way or to make longitudinal assessments of adaptive changes at the motoneuron level. These studies assessed the reliability of responses produced by magnetic stimulation of the corticospinal tract. Cervicomedullary motor evoked potentials (CMEPs) were recorded in the first dorsal interosseus (FDI) on 2 separate days. On each day, four sets of stimuli were delivered at the maximal output of the stimulator, with the final two sets ≥10 min after the initial sets. Sets of stimuli were also delivered at different stimulus intensities to obtain stimulus-response curves. In addition, on the second day, responses at different stimulus intensities were evoked during weak voluntary contractions. Responses were normalized to the maximal muscle compound action potential ( Mmax). CMEPs evoked in the relaxed FDI were small, even when stimulus intensity was maximal (3.6 ± 2.5% Mmax) but much larger during a weak contraction (e.g., 26.2 ± 10.2% Mmax). CMEPs evoked in the relaxed muscle at the maximal output of the stimulator were highly reproducible both within (ICC = 0.83, session 1; ICC = 0.87, session 2) and between sessions (ICC = 0.87). ICCs for parameters of the input-output curves, which included measures of motor threshold, slope, and maximal response size, ranged between 0.87 and 0.62. These results suggest that responses to magnetic stimulation of the corticospinal tract can be assessed in relaxation and contraction and can be reliably obtained for longitudinal studies of motoneuronal excitability.

Increased corticospinal excitability prior to arm cycling is due to enhanced supraspinal but not spinal motoneurone excitability

2013 ◽  
Vol 38 (11) ◽  
pp. 1154-1161 ◽  
Author(s):  
Kevin E. Power ◽  
David B. Copithorne
Keyword(s):  
Magnetic Stimulation ◽  
Corticospinal Tract ◽  
Biceps Brachii ◽  
Motor Evoked Potentials ◽  
Corticospinal Excitability ◽  
Quiescent State ◽  
M Wave ◽  
Arm Cycling ◽  
Intention To Move ◽  
Stimulation Of

Human studies have not assessed supraspinal or spinal motoneurone excitability in the quiescent state prior to a rhythmic and alternating cyclical motor output. The purpose of the current study was to determine whether supraspinal and (or) spinal motoneurone excitability was modulated in humans prior to arm cycling when compared with rest with no intention to move. We hypothesized that corticospinal excitability would be enhanced prior to arm cycling due, in part, to increased spinal motoneurone excitability. Supraspinal and spinal motoneurone excitability were assessed via transcranial magnetic stimulation (TMS) of the motor cortex and transmastoid stimulation of the corticospinal tract, respectively. Surface electromyography recordings of TMS motor evoked potentials (MEPs) and cervicomedullary MEPs (CMEPs) were made from the relaxed biceps brachii muscle prior to rhythmic arm cycling and at rest with no intention to move. The amplitude of the MEPs was greater (mean increase: +9.8% of maximal M wave; p = 0.006) and their onset latencies were shorter (mean decrease: –1.5 ms; p < 0.05) prior to cycling when compared with rest. The amplitudes of the CMEPs at any of 3 stimulation intensities were not different between conditions. We conclude that premovement enhancement of corticospinal excitability is greater prior to arm cycling than at rest because of increases in supraspinal but not spinal motoneurone excitability.

scholarly journals Physical activity modulates corticospinal excitability of the lower limb in young and old adults

2017 ◽  
Vol 123 (2) ◽  
pp. 364-374 ◽  
Author(s):  
Hamidollah Hassanlouei ◽  
Christopher W. Sundberg ◽  
Ashleigh E. Smith ◽  
Andrew Kuplic ◽  
Sandra K. Hunter
Keyword(s):  
Physical Activity ◽  
Nervous System ◽  
Lower Limb ◽  
Magnetic Stimulation ◽  
Corticospinal Tract ◽  
Corticospinal Excitability ◽  
Response Curves ◽  
Old Adults ◽  
Stimulus Response ◽  
Optimal Health

Aging is associated with reduced neuromuscular function, which may be due in part to altered corticospinal excitability. Regular physical activity (PA) may ameliorate these age-related declines, but the influence of PA on corticospinal excitability is unknown. The purpose of this study was to determine the influence of age, sex, and PA on corticospinal excitability by comparing the stimulus-response curves of motor evoked potentials (MEP) in 28 young (22.4 ± 2.2 yr; 14 women and 14 men) and 50 old adults (70.2 ± 6.1 yr; 22 women and 28 men) who varied in activity levels. Transcranial magnetic stimulation was used to elicit MEPs in the active vastus lateralis muscle (10% maximal voluntary contraction) with 5% increments in stimulator intensity until the maximum MEP amplitude. Stimulus-response curves of MEP amplitudes were fit with a four-parameter sigmoidal curve and the maximal slope calculated (slopemax). Habitual PA was assessed with tri-axial accelerometry and participants categorized into either those meeting the recommended PA guidelines for optimal health benefits (>10,000 steps/day, high-PA; n = 21) or those not meeting the guidelines (<10,000 steps/day, low-PA; n = 41). The MEP amplitudes and slopemax were greater in the low-PA compared with the high-PA group ( P < 0.05). Neither age nor sex influenced the stimulus-response curve parameters ( P > 0.05), suggesting that habitual PA influenced the excitability of the corticospinal tract projecting to the lower limb similarly in both young and old adults. These findings provide evidence that achieving the recommended PA guidelines for optimal health may mediate its effects on the nervous system by decreasing corticospinal excitability. NEW & NOTEWORTHY Transcranial magnetic stimulation was used to determine whether achieving the recommended 10,000 steps/day for optimal health influenced the excitability of the corticospinal tract projecting to the knee extensor muscles. Irrespective of age and sex, individuals who achieved >10,000 steps/day had lower corticospinal excitability than those who performed <10,000 steps/day, possibly representing greater control of inhibitory and excitatory networks. Physical activity involving >10,000 steps/day may mediate its effects on the nervous system by decreasing corticospinal excitability.

scholarly journals Differential effects of aging and physical activity on corticospinal excitability of upper and lower limb muscles

2019 ◽  
Vol 122 (1) ◽  
pp. 241-250 ◽  
Author(s):  
Vianney Rozand ◽  
Jonathon W. Senefeld ◽  
Christopher W. Sundberg ◽  
Ashleigh E. Smith ◽  
Sandra K. Hunter
Keyword(s):  
Physical Activity ◽  
Lower Limb ◽  
Magnetic Stimulation ◽  
Corticospinal Tract ◽  
Vastus Lateralis ◽  
Corticospinal Excitability ◽  
Response Curves ◽  
Stimulus Response ◽  
Lower Limb Muscles ◽  
Limb Muscles

Corticospinal tract excitability can be altered by age, physical activity (PA), and possibly sex, but whether these effects differ between upper and lower limb muscles is unknown. We determined the influence of age, PA, and sex on corticospinal excitability of an upper limb and a lower limb muscle during submaximal contractions by comparing stimulus-response curves of motor evoked potentials (MEPs). Transcranial magnetic stimulation (TMS) was used to evoke stimulus-response curves in active muscles by incrementally increasing the stimulator intensity from below the active motor threshold (AMT) until a plateau in MEP amplitudes was achieved. Stimulus-response curves were analyzed from the first dorsal interosseous (FDI) of 30 young (23.9 ± 3.8 yr) and 33 older (72.6 ± 5.6 yr) men and women and the vastus lateralis (VL) of 13 young (23.2 ± 2.2 yr) and 25 older (72.7 ± 5.5 yr) men and women. Corticospinal excitability was determined by fitting the curves with a four-parameter sigmoidal curve and calculating the maximal slope (slopemax). PA was assessed with triaxial accelerometry, and participants were dichotomized into high-PA (>10,000 steps/day, n = 15) or low-PA (<10,000 steps/day, n = 43) groups. Young adults had larger FDI MEP amplitudes (% maximum amplitude of compound muscle action potential) at higher TMS intensities (120–150% AMT) and greater slopemax than older adults ( P < 0.05), with no differences between high- and low-PA groups ( P > 0.05). VL MEP amplitudes and slopemax, however, were lower in the high-PA than low-PA participants, with no age or sex differences. These data suggest that aging and PA, but not sex, differentially influence the excitability of the corticospinal tracts projecting to muscles of the upper compared with the lower limb. NEW & NOTEWORTHY Excitability of the corticospinal tract projecting to the first dorsal interosseous assessed with transcranial magnetic stimulation was reduced with age but independent of regular physical activity (steps/day) and sex of the individual. In contrast, corticospinal excitability of the vastus lateralis was not affected by age but was reduced in individuals achieving more than the physical activity recommendations of 10,000 steps/day. Aging and activity differentially affect corticospinal excitability of upper and lower limb muscles.

Mechanisms of airway hypercontractility in basenji-greyhound dogs

1987 ◽  
Vol 63 (5) ◽  
pp. 2008-2014 ◽  
Author(s):  
T. M. Murphy ◽  
N. M. Munoz ◽  
C. A. Hirshman ◽  
J. S. Blake ◽  
A. R. Leff
Keyword(s):  
Maximal Response ◽  
Adrenergic Blockade ◽  
Vagus Nerves ◽  
Response Curves ◽  
Bronchial Smooth Muscle ◽  
Muscarinic Response ◽  
Contractile Forces ◽  
Stimulation Of

The comparative effects of contractile agonists and physiological stimulation of the tracheal and bronchial smooth muscle (BSM) response were studied isometrically in situ in five Basenji-greyhound (BG) and six mongrel dogs. Frequency-response curves generated by bilateral stimulation of the vagus nerves (0–20 Hz, 15–20 V, 2-ms duration) elicited greater maximal contraction in mongrel trachea (36.8 +/- 8.1 vs. 26.9 +/- 4.0 g/cm; P less than 0.02) and exhibited greater responsiveness in mongrel BSM (half-maximal response to electrical stimulation 3.0 +/- 1.1 vs. 7.0 +/- 0.5 Hz; P less than 0.05) compared with BG dogs. However, muscarinic sensitivity to intravenous methacholine (MCh) was substantially greater in BG dogs; MCh caused contraction greater than 1.5 g/cm at a mean dose of 3.0 X 10(-10) mol/kg for BG dogs compared with 5.1 X 10(-9) mol/kg for mongrel controls (P less than 0.03, Mann-Whitney rank-sum test). In contrast to the muscarinic response, the contractile response elicited by intravenous norepinephrine after beta-adrenergic blockade was similar in trachea and bronchus for both mongrel and BG dogs. Our data confirm previous in vitro demonstration of tracheal hyporesponsiveness in BG dogs and demonstrate that the contraction resulting from efferent parasympathetic stimulation is less in the BG than mongrel dogs. However, postsynaptic muscarinic responsiveness of BG BSM is substantially increased. We conclude that a component of airway responsiveness in BG dogs depends directly on contractile forces generated postsynaptically that are nongeometry dependent, postjunctional, and agonist specific.

High-intensity, low-frequency repetitive transcranial magnetic stimulation enhances excitability of the human corticospinal pathway

2020 ◽  
Vol 123 (5) ◽  
pp. 1969-1978
Author(s):  
Jessica M. D’Amico ◽  
Siobhan C. Dongés ◽  
Janet L. Taylor
Keyword(s):  
Transcranial Magnetic Stimulation ◽  
High Intensity ◽  
Magnetic Stimulation ◽  
Corticospinal Tract ◽  
Motor Evoked Potentials ◽  
Repetitive Transcranial Magnetic Stimulation ◽  
Low Frequency ◽  
Intracortical Inhibition ◽  
Corticospinal Pathway ◽  
Plastic Changes

In this study, we present a novel, intensity-dependent repetitive transcranial magnetic stimulation (rTMS) protocol that induces lasting, plastic changes within the corticospinal tract. High-intensity rTMS at a frequency of 0.1 Hz induces facilitation of motor evoked potentials (MEPs) lasting at least 35 min. Additionally, these changes are not limited only to small MEPs but occur throughout the recruitment curve. Finally, facilitation of MEPs following high-intensity rTMS does not appear to be due to changes in intracortical inhibition or facilitation.

scholarly journals Studies on the Corticospinal Control of Human Walking. I. Responses to Focal Transcranial Magnetic Stimulation of the Motor Cortex

1999 ◽  
Vol 81 (1) ◽  
pp. 129-139 ◽  
Author(s):  
Charles Capaday ◽  
Brigitte A. Lavoie ◽  
Hugues Barbeau ◽  
Cyril Schneider ◽  
Mireille Bonnard
Keyword(s):  
Motor Cortex ◽  
Magnetic Stimulation ◽  
Stance Phase ◽  
Corticospinal Tract ◽  
Human Walking ◽  
Step Cycle ◽  
Motor Circuits ◽  
Significant Difference ◽  
Stimulation Of

Capaday, Charles, Brigitte A. Lavoie, Hugues Barbeau, Cyril Schneider, and Mireille Bonnard. Studies on the corticospinal control of human walking. I. Responses to focal transcranial magnetic stimulation of the motor cortex. J. Neurophysiol. 81: 129–139, 1999. Experiments were done to determine the extent to which the corticospinal tract is linked with the segmental motor circuits controlling ankle flexors and extensors during human walking compared with voluntary motor tasks requiring attention to the level of motor activity. The motor cortex was activated transcranially using a focal magnetic stimulation coil. For each subject, the entire input-output (I-O) curve [i.e., the integral of the motor evoked-potential (MEP) versus stimulus strength] was measured during a prescribed tonic voluntary contraction of either the tibialis anterior (TA) or the soleus. Similarly, I-O curves were measured in the early part of the swing phase, or in the early part of the stance phase of walking. The I-O data points were fitted by the Boltzmann sigmoidal function, which accounted for ≥80% of total data variance. There was no statistically significant difference between the I-O curves of the TA measured during voluntary ankle dorsiflexion or during the swing phase of walking, at matched levels of background electromyographic (EMG) activity. Additionally, there was no significant difference in the relation between the coefficient of variation and the amplitude of the MEPs measured in each task, respectively. In comparison, during the stance phase of walking the soleus MEPs were reduced on average by 26% compared with their size during voluntary ankle plantarflexion. Furthermore, during stance the MEPs in the inactive TA were enhanced relative to their size during voluntary ankle plantarflexion and in four of six subjects the TA MEPs were larger than those of the soleus. Finally, stimulation of the motor cortex at various phases of the step cycle did not reset the cycle. The time of the next step occurred at the expected moment, as determined from the phase-resetting curve. One interpretation of this result is that the motor cortex may not be part of the central neural system involved in timing the motor bursts during the step cycle. We suggest that during walking the corticospinal tract is more closely linked with the segmental motor circuits controlling the flexor, TA, than it is with those controlling the extensor, soleus. However, during voluntary tasks requiring attention to the level of motor activity, it is equally linked with the segmental motor circuits of ankle flexors or extensors.

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