title: Amplification of interlimb reflexes evoked by stimulating the hand simultaneously with conditioning from the foot during locomotion.
abstract: 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.
authors.affiliation: Department of Integrative Physiology, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Japan.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Nakajima
authors.forename: Trevor
authors.initials: T
authors.lastname: Barss
authors.forename: Taryn
authors.initials: T
authors.lastname: Klarner
authors.forename: Tomoyoshi
authors.initials: T
authors.lastname: Komiyama
authors.forename: E Paul
authors.initials: EP
authors.lastname: Zehr
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D005528:Foot / Q000294:innervation*; D006225:Hand / Q000294:innervation*; D006801:Humans; D008124:Locomotion / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology; D010543:Peroneal Nerve / Q000502:physiology; D012018:Reflex / Q000502:physiology*; D055815:Young Adult