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Temporal Profile and Limb-specificity of Phasic Pain-Evoked Changes in Motor Excitability

M Algoet1, J Duque1, G D Iannetti2

  • 1Institute of Neuroscience (IoNS), Université catholique de Louvain, Brussels, Belgium.

Neuroscience
|July 19, 2018
PubMed

Insights

Phasic pain briefly enhances motor excitability in muscles controlling the stimulated limb, followed by widespread inhibition. Long-lasting pain signals also increase motor excitability in the non-stimulated limb, suggesting complex nociception-motor interactions.

Area of Science:

  • Neuroscience
  • Motor Control
  • Pain Perception

Background:

  • Nociception, the sensory nervous system's process of encoding noxious stimuli, is crucial for triggering defensive motor responses.
  • Understanding how acute pain influences motor excitability is vital for comprehending protective reflexes and potential maladaptive changes.

Purpose of the Study:

  • To investigate the effects of short-lasting (phasic) pain on the motor excitability of muscles in both the ipsilateral and contralateral arms.
  • To determine the temporal dynamics of nociception-motor interactions following a painful stimulus.

Main Methods:

  • Utilized transcranial magnetic stimulation (TMS) to measure motor-evoked potentials (MEPs) in flexor and extensor muscles of both arms.
  • Delivered short-lasting nociceptive laser stimuli to either the left or right hand.
  • Triggered TMS pulses at various intervals (50-2000 ms) post-stimulus to map the time course of effects.

Main Results:

  • An early enhancement (around 100 ms) of MEPs was observed in flexor muscles of the stimulated hand, indicative of spinal-level nociception-motor interactions.
  • A later reduction in MEPs occurred in extensor muscles of the stimulated limb and flexor muscles of both limbs (150-400 ms).
  • A long-lasting enhancement of MEPs was noted in the non-stimulated hand (600-2000 ms), suggesting cortical involvement.

Conclusions:

  • Phasic pain transiently modulates motor excitability in a time- and limb-dependent manner.
  • Early effects appear mediated at the spinal level, while later, longer-lasting effects may involve cortical processing.
  • These findings illuminate the complex interplay between pain perception and motor system activation for defensive behaviors.
Keywords:
motor-evoked potentialsnociceptionpainprimary motor cortextranscranial magnetic stimulation

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