Sensory afferent inhibition within and between limbs in humans

Abstract Objective To examine the distribution and inter-limb interaction of short-latency afferent inhibition (SAI) in the arm and leg. Methods Motor evoked potentials (MEPs) in distal and proximal arm, shoulder and leg muscles induced with ranscranial magnetic stimulation (TMS) were conditioned by...

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Bibliographic Details
Published in:Clinical neurophysiology 2009-03, Vol.120 (3), p.610-618
Main Authors: Bikmullina, R, Bäumer, T, Zittel, S, Münchau, A
Format: Article
Language:English
Subjects:
Adult
Afferent Pathways - physiology
Arm - innervation
Arm - physiology
Biological and medical sciences
Electric Stimulation
Electrodiagnosis. Electric activity recording
Evoked Potentials, Motor - physiology
Extremities - innervation
Extremities - physiology
Female
Fundamental and applied biological sciences. Psychology
Humans
Investigative techniques, diagnostic techniques (general aspects)
Leg - innervation
Leg - physiology
Male
Medical sciences
Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration
Motor Cortex - physiology
Nervous system
Neural Inhibition - physiology
Neurology
Reaction Time - physiology
Sensorimotor integration
Sensory Thresholds - physiology
Short afferent inhibition
Skin - innervation
Thalamus - physiology
Time Factors
Toes - innervation
Toes - physiology
Transcranial Magnetic Stimulation
Vertebrates: nervous system and sense organs
Young Adult
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Summary:Abstract Objective To examine the distribution and inter-limb interaction of short-latency afferent inhibition (SAI) in the arm and leg. Methods Motor evoked potentials (MEPs) in distal and proximal arm, shoulder and leg muscles induced with ranscranial magnetic stimulation (TMS) were conditioned by painless electrical stimuli applied to the index finger (D2) and great toe (T1) at interstimulus intervals (ISIs) of 15, 25–35, 80 ms (D2) and 35, 45, 55, 65 and 100 ms (T1) in 27 healthy human subjects. TMS was delivered over primary motor cortex (M1) arm and leg areas. Electrical stimulus intensities were varied between 1 and 3 times the sensory perception thresholds. We also tested effects of posterior cutaneous brachial nerve (PCBN) stimulation on MEPs in arm muscles at ISIs of 18 and 28 ms. Results D2 but not PCBN electrical conditioning reduced MEP amplitudes in upper limb muscles at ISIs of 25 and 35 ms. SAI was more pronounced in distal as compared to proximal arm muscles. Also, SAI following D2 stimulation increased with higher conditioning intensities. D2 stimulation did not change lower limb muscles MEPs. In ontrast, T1 stimulation did not induce SAI in any muscles but caused MEP facilitation in a foot muscle at an ISI of 55 ms and in upper limb muscles at ISIs of 35 and 55 ms. Short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were not affected by electrical T1 conditioning. Conclusion D2 stimulation causes segmental SAI in upper limb muscles with a distal to proximal attenuation without affecting leg muscles. In contrast, toe stimulation facilitates motor output both in foot and upper arm muscles. Significance Our data suggest that cutaneo-motor pathways in arms and legs are functionally organized in a different way with cutaneo-motor interactions induced by toe stimulation probably relayed at a thalamic level. Abnormal cutaneo-motor interactions following electrical toe stimulation may serve as an electrophysiological marker of thalamic dysfunction, e.g. in neurodegenerative diseases.
ISSN:1388-2457
1872-8952
DOI:10.1016/j.clinph.2008.12.003