title: A common neural element receiving rhythmic arm and leg activity as assessed by reflex modulation in arm muscles.
abstract: Neural interactions between regulatory systems for rhythmic arm and leg movements are an intriguing issue in locomotor neuroscience. Amplitudes of early latency cutaneous reflexes (ELCRs) in stationary arm muscles are modulated during rhythmic leg or arm cycling but not during limb positioning or voluntary contraction. This suggests that interneurons mediating ELCRs to arm muscles integrate outputs from neural systems controlling rhythmic limb movements. Alternatively, outputs could be integrated at the motoneuron and/or supraspinal levels. We examined whether a separate effect on the ELCR pathways and cortico-motoneuronal excitability during arm and leg cycling is integrated by neural elements common to the lumbo-sacral and cervical spinal cord. The subjects performed bilateral leg cycling (LEG), contralateral arm cycling (ARM), and simultaneous contralateral arm and bilateral leg cycling (A&L), while ELCRs in the wrist flexor and shoulder flexor muscles were evoked by superficial radial (SR) nerve stimulation. ELCR amplitudes were facilitated by cycling tasks and were larger during A&L than during ARM and LEG. A low stimulus intensity during ARM or LEG generated a larger ELCR during A&L than the sum of ELCRs during ARM and LEG. We confirmed this nonlinear increase in single motor unit firing probability following SR nerve stimulation during A&L. Furthermore, motor-evoked potentials following transcranial magnetic and electrical stimulation did not show nonlinear potentiation during A&L. These findings suggest the existence of a common neural element of the ELCR reflex pathway that is active only during rhythmic arm and leg movement and receives convergent input from contralateral arms and legs.
authors.affiliation: Division of Health and Sport Education, The United Graduate School of Education, Tokyo Gakugei University, Tokyo, Japan; Department of Food and Nutrition Science, Sagami Women's University, Kanagawa, Japan; Sasada_syusaku@isc.sagami-wu.ac.jp.
authors.forename: Syusaku
authors.initials: S
authors.lastname: Sasada
authors.affiliation: The Miami Project to Cure Paralysis, Miller School of Medicine, University of Miami, Miami, Florida;
authors.forename: Toshiki
authors.initials: T
authors.lastname: Tazoe
authors.affiliation: Department of Integrative Physiology, Kyorin University School of Medicine, Tokyo, Japan;
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Nakajima
authors.affiliation: Division of Health and Sport Education, The United Graduate School of Education, Tokyo Gakugei University, Tokyo, Japan; Department of Management and Information Sciences, Jobu University, Gunma, Japan;
authors.forename: Genki
authors.initials: G
authors.lastname: Futatsubashi
authors.affiliation: School of Rehabilitation Sciences, Health Sciences University of Hokkaido, Hokkaido, Japan;
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohtsuka
authors.affiliation: Division of Health and Sport Education, The United Graduate School of Education, Tokyo Gakugei University, Tokyo, Japan; Department of Integrative Physiology, Kyorin University School of Medicine, Tokyo, Japan;
authors.forename: Shinya
authors.initials: S
authors.lastname: Suzuki
authors.affiliation: Rehabilitation Neuroscience Laboratory, University of Victoria, Victoria, British Columbia, Canada; and.
authors.forename: E Paul
authors.initials: EP
authors.lastname: Zehr
authors.affiliation: Division of Health and Sport Education, The United Graduate School of Education, Tokyo Gakugei University, Tokyo, Japan; Department of Health and Sports Sciences, Faculty of Education, Chiba University, Chiba, Japan.
authors.forename: Tomoyoshi
authors.initials: T
authors.lastname: Komiyama
mesh_terms: D000328:Adult; D001132:Arm / Q000294:innervation / Q000502:physiology*; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D007395:Interneurons / Q000502:physiology; D007866:Leg / Q000294:innervation / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000166:cytology / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology; D009068:Movement; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D012018:Reflex; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology
keywords: cutaneous reflex; interlimb interaction; locomotion; rhythm-generating system