Amplification of interlimb reflexes evoked by stimulating the hand simultaneously with conditioning from the foot during locomotion. 2013

Tsuyoshi Nakajima, and Trevor Barss, and Taryn Klarner, and Tomoyoshi Komiyama, and E Paul Zehr
Department of Integrative Physiology, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Japan.

BACKGROUND Widespread interlimb reflexes evoked in leg muscles by cutaneous stimulation of the hand are phase-modulated and behaviorally relevant to produce functional changes in ankle trajectory during walking. These reflexes are complementary to the segmental responses evoked by stimulation at the ankle. Despite differences in the expression of reflex amplitude based upon site of nerve stimulation, there are some common features as well, suggesting the possibility of shared interneuronal pathways. Currently little is known about integration or shared reflex systems from interlimb cutaneous networks during human locomotion. Here we investigated convergent reflex effects following cutaneous stimulation of the hand and foot during arm and leg cycling (AL) by using spatial facilitation. Participants performed AL cycling and static activation of the target muscle knee extensor vastus lateralis (VL) in 3 different randomly ordered nerve stimulation conditions: 1) superficial radial nerve (SR; input from hand); 2) superficial peroneal nerve (SP; input from foot); and, 3) combined stimulation (SR + SP). Stimuli were applied around the onset of rhythmic EMG bursts in VL corresponding to the onset of the power or leg extension phase. RESULTS During AL cycling, small inhibitory (~80 ms) and large facilitatory reflexes (~100 ~ 150 ms) were seen in VL. The amplitudes of the facilitatory responses with SR + SP stimulation were significantly larger than those for SP or SR stimulation alone. The facilitation was also significantly larger than the simple mathematical summation of amplitudes from SP and SR trials. This indicates extra facilitation beyond what would be accounted for by serial neuronal processing and was not observed during static activation. CONCLUSIONS We conclude that AL cycling activates shared interneurons in convergent reflex pathways from cutaneous inputs innervating the hand and leg. This enhanced activity has functional implications for corrective responses during locomotion and for translation to rehabilitation after neurotrauma.

UI MeSH Term Description Entries
D008124 Locomotion Movement or the ability to move from one place or another. It can refer to humans, vertebrate or invertebrate animals, and microorganisms. Locomotor Activity,Activities, Locomotor,Activity, Locomotor,Locomotor Activities
D008297 Male Males
D008875 Middle Aged An adult aged 45 - 64 years. Middle Age
D010543 Peroneal Nerve The lateral of the two terminal branches of the sciatic nerve. The peroneal (or fibular) nerve provides motor and sensory innervation to parts of the leg and foot. Fibular Nerve,Fibular Nerves,Nerve, Fibular,Nerve, Peroneal,Nerves, Fibular,Nerves, Peroneal,Peroneal Nerves
D012018 Reflex An involuntary movement or exercise of function in a part, excited in response to a stimulus applied to the periphery and transmitted to the brain or spinal cord.
D004558 Electric Stimulation Use of electric potential or currents to elicit biological responses. Stimulation, Electric,Electrical Stimulation,Electric Stimulations,Electrical Stimulations,Stimulation, Electrical,Stimulations, Electric,Stimulations, Electrical
D004576 Electromyography Recording of the changes in electric potential of muscle by means of surface or needle electrodes. Electromyogram,Surface Electromyography,Electromyograms,Electromyographies,Electromyographies, Surface,Electromyography, Surface,Surface Electromyographies
D005260 Female Females
D005528 Foot The distal extremity of the leg in vertebrates, consisting of the tarsus (ANKLE); METATARSUS; phalanges; and the soft tissues surrounding these bones. Feet
D006225 Hand The distal part of the arm beyond the wrist in humans and primates, that includes the palm, fingers, and thumb. Hands

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