title: Nociceptive fingertip stimulation inhibits synergistic motoneuron pools in the human upper limb.
abstract: BACKGROUND
  Activation of distinct muscle groups organized in a stereotyped manner ("muscle synergies") is thought to underlie the production of movement by the vertebrate spinal cord. This results in movement with minimum effort and maximum efficiency. The question of how the vertebrate nervous system inhibits ongoing muscle activity is central to the study of the neural control of movement.
  
  
  OBJECTIVE
  To investigate the strategy used by the human spinal cord to rapidly inhibit muscle activation in the upper limb.
  
  
  METHODS
  The authors performed a series of experiments in 10 healthy subjects to assess the effect of nociceptive cutaneous stimulation on voluntarily contracting upper limb muscles. They recorded the electromyogram (EMG) with surface electrodes placed over various upper limb muscles.
  
  
  RESULTS
  The authors found evidence of a simple inhibitory strategy that 1) was dependent on the intensity of the stimulus, 2) was maximally evoked when stimulation was applied to the fingertips, 3) preceded the earliest onset of voluntary muscle relaxation, and 4) produced inhibition of EMG activity in specific upper limb muscle groups. Nociceptive fingertip stimulation preferentially inhibited contraction of synergistic muscles involved in reaching and grasping (intrinsic hand muscles, forearm flexors, triceps) while having little effect on biceps or deltoid.
  
  
  CONCLUSIONS
  Neural circuitry within the human spinal cord is organized to inhibit movement by rapidly deactivating muscles that constitute distinct muscle synergies. This strategy of selective and concurrent deactivation of the same basic elements that produce synergistic movement greatly simplifies motor control.
authors.affiliation: Center for Neuroscience and Neurological Recovery, Mississipi Methodist Rehabilitation Center, Jackson 39216, USA.
authors.forename: A A
authors.initials: AA
authors.lastname: Leis
authors.forename: D S
authors.initials: DS
authors.lastname: Stokic
authors.forename: P
authors.initials: P
authors.lastname: Fuhr
authors.forename: M
authors.initials: M
authors.lastname: Kofler
authors.forename: M F
authors.initials: MF
authors.lastname: Kronenberg
authors.forename: J
authors.initials: J
authors.lastname: Wissel
authors.forename: F X
authors.initials: FX
authors.lastname: Glocker
authors.forename: C
authors.initials: C
authors.lastname: Seifert
authors.forename: I
authors.initials: I
authors.lastname: Stetkarova
mesh_terms: D000328:Adult; D001132:Arm / Q000502:physiology*; D004576:Electromyography; D005260:Female; D006225:Hand / Q000502:physiology; D006801:Humans; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D009132:Muscles / Q000502:physiology; D009619:Nociceptors / Q000502:physiology*; D010812:Physical Stimulation; D013116:Spinal Cord / Q000502:physiology*