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Author Notes:

Corresponding author: Trisha Kesar, 1441 Clifton Rd NE, Emory Rehabilitation Hospital, Atlanta, Georgia 30322, USA. tkesar@emory.edu

JWS is supported by the Faculty of Science, University of Auckland, New Zealand.

We would like to thank Dr. Michael R. Borich and Dr. Jiang Xu for providing valuable critiques for the manuscript draft, and Steven Eicholtz for assisting with preparation of the figures.

The Authors declare that there are no conflicts of interest.

Subject:

Research Funding:

TMK is supported by the National Institute of Child Health and Human Development grant number K01 HD079584.

SLW is supported by grants U10NS086607 and U01 NS091951.

Keywords:

  • Science & Technology
  • Life Sciences & Biomedicine
  • Neurosciences
  • Neurosciences & Neurology
  • Neuroplasticity
  • non-invasive brain stimulation
  • leg muscles
  • homunculus
  • motor cortex
  • gait
  • posture
  • HUMAN MOTOR CORTEX
  • TIBIALIS ANTERIOR MUSCLE
  • VASTUS LATERALIS MUSCLE
  • CORTICOSPINAL EXCITABILITY
  • EVOKED-POTENTIALS
  • CHRONIC STROKE
  • SOLEUS MUSCLE
  • INTRACORTICAL INHIBITION
  • PYRAMIDAL TRACT
  • CORTICOMOTOR EXCITABILITY

The use of transcranial magnetic stimulation to evaluate cortical excitability of lower limb musculature: Challenges and opportunities

Tools:

Journal Title:

Restorative Neurology and Neuroscience

Volume:

Volume 36, Number 3

Publisher:

, Pages 333-348

Type of Work:

Article | Post-print: After Peer Review

Abstract:

Neuroplasticity is a fundamental yet relatively unexplored process that can impact rehabilitation of lower extremity (LE) movements. Transcranial magnetic stimulation (TMS) has gained widespread application as a non-invasive brain stimulation technique for evaluating neuroplasticity of the corticospinal pathway. However, a majority of TMS studies have been performed on hand muscles, with a paucity of TMS investigations focused on LE muscles. This perspective review paper proposes that there are unique methodological challenges associated with using TMS to evaluate corticospinal excitability of lower limb muscles. The challenges include: (1) the deeper location of the LE motor homunculus; (2) difficulty with targeting individual LE muscles during TMS; and (3) differences in corticospinal circuity controlling upper and lower limb muscles. We encourage future investigations that modify traditional methodological approaches to help address these challenges. Systematic TMS investigations are needed to determine the extent of overlap in corticomotor maps for different LE muscles. A simple, yet informative methodological solution involves simultaneous recordings from multiple LE muscles, which will provide the added benefit of observing how other relevant muscles co-vary in their responses during targeted TMS assessment directed toward a specific muscle. Furthermore, conventionally used TMS methods (e.g., determination of hot spot location and motor threshold) may need to be modified for TMS studies involving LE muscles. Additional investigations are necessary to determine the influence of testing posture as well as activation state of adjacent and distant LE muscles on TMS-elicited responses. An understanding of these challenges and solutions specific to LE TMS will improve the ability of neurorehabilitation clinicians to interpret TMS literature, and forge novel future directions for neuroscience research focused on elucidating neuroplasticity processes underlying locomotion and gait training.

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© 2018 - IOS Press and the authors. All rights reserved.

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