title: Downregulating Aberrant Motor Evoked Potential Synergies of the Lower Extremity Post Stroke During TMS of the Contralesional Hemisphere.
abstract: Growing evidence demonstrates unique synergistic signatures in the lower limb (LL) post-stroke, with specific across-plane and across-joint representations. While the inhibitory role of the ipsilateral hemisphere in the upper limb (UL) has been widely reported, examination of the contralesional hemisphere (CON-H) in modulating LL expressions of synergies following stroke is lacking.
  
  
  
  We hypothesize that stimulation of lesioned and contralesional motor cortices will differentially regulate paretic LL motor outflow. We propose a novel TMS paradigm to identify synergistic motor evoked potential (MEP) patterns across multiple muscles.
  
  
  
  Amplitude and background activation matched adductor MEPs were elicited using single pulse TMS of L-H and CON-H (control ipsilateral) during an adductor torque matching task from 11 stroke and 10 control participants. Associated MEPs of key synergistic muscles were simultaneously observed.
  
  
  
  By quantifying CON-H/L-H MEP ratios, we characterized a significant targeted inhibition of aberrant MEP coupling between ADD and VM (p = 0.0078) and VL (p = 0.047) exclusive to the stroke group (p = 0.028) that was muscle dependent (p = 0.039). We find TA inhibition in both groups following ipsilateral hemisphere stimulation (p = 0.0014; p = 0.015).
  
  
  
  We argue that ipsilaterally mediated attenuation of abnormal synergistic activations post stroke may reflect an adaptive intracortical inhibition. The predominance of sub 3ms interhemispheric MEP latency differences implicates LL ipsilateral corticomotor projections. These findings provide insight into the association between CON-H reorganization and post-stroke LL recovery. While a prevailing view of driving L-H disinhibition for UL recovery seems expedient, presuming analogous LL neuromodulation may require further examination for rehabilitation. This study provides a step toward this goal.
authors.affiliation: Northwestern University Interdepartmental Neuroscience, Northwestern University, Chicago, IL, USA; Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL, USA. Electronic address: aqt@u.northwestern.edu.
authors.forename: Andrew Q
authors.initials: AQ
authors.lastname: Tan
authors.affiliation: School of Physical Education, Sport and Exercise Science, University of Otago, Dunedin, New Zealand.
authors.forename: Jon
authors.initials: J
authors.lastname: Shemmell
authors.affiliation: Northwestern University Interdepartmental Neuroscience, Northwestern University, Chicago, IL, USA; Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL, USA; Department of Biomedical Engineering, Northwestern University, Chicago, IL, USA.
authors.forename: Yasin Y
authors.initials: YY
authors.lastname: Dhaher
mesh_terms: D000328:Adult; D000368:Aged; D015536:Down-Regulation / Q000502:physiology; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D035002:Lower Extremity / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology / Q000503:physiopathology*; D020521:Stroke / Q000175:diagnosis / Q000503:physiopathology* / Q000628:therapy*; D000071939:Stroke Rehabilitation; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult
keywords: Contralesional hemisphere; Lower limb; Muscle synergies; Stroke; Transcranial magnetic stimulation