Characterizing Multiple MEPs Induced by TMS over the Dominant and NonDominant Motor Cortex

1
Characterizing Multiple MEPs Induced by TMS over
the Dominant and Non-Dominant Motor Cortex Paul
van Donkelaar1, Katy Baden2 Jeanne
Langan1 Departments of Human Physiology1 and
Biology2, University of Oregon
992.2
INTRODUCTION
METHODS
RESULTS
Across the 3 stimulation intensities extremely
right-handed subjects displayed significantly
different FDI/APB MEP ratios across the dominant
and non-dominant hand. This was not the case in
non right-handed subjects.
This asymmetry was also reflected in handedness
scores and pegboard performance.

• Movements of the dominant hand tend to be finer
  and more smoothly coordinated than movements of
  the non-dominant hand this is especially true
  in extremely handed people.
• This implies that the representation of the
  dominant hand/fingers in the motor cortex (M1)
  may be larger than that of the non-dominant hand.
• Previous studies examining motor evoked
  potentials (MEPs) generated with transcranial
  magnetic stimulation (TMS) over the motor cortex
  have generally not shown differences across the
  dominant and non-dominant hemispheres.
• Thus, more finely coordinated movements may
  result from the representation of individual
  fingers being more interdigitated in the dominant
  hemisphere.
• This predicts that simultaneous MEPs in multiple
  muscles may be more likely in the dominant hand
  and this may be more apparent in extremely
  right-handed subjects.

• 18 subjects 9 right-handed 9
  left-handed/ambidextrous
• Handedness determined with Edinburgh Handedness
  questionnaire.
• TMS delivered at 110, 120, 130 of motor
  threshold for first dorsal interrosseous (FDI)
  over dominant and non-dominant M1.
• Peak-to-peak MEP amplitude measured
  simultaneously in FDI, abductor digiti minimi
  (ADM) and the abductor pollicis brevis (APB) of
  each hand.

RESULTS EXTREMELY RIGHT-HANDED SUBJECT
110
FDI
Dominant Hand
APB
ADM
FDI
CONCLUSIONS
FINGER REPRESENTATIONS EXTREMELY RIGHT-HANDED
Non-Dominant Hand
APB

• These data are consistent with a more elaborate
  and interdigitated finger representation in the
  motor cortex of the dominant hemisphere in
  extremely right-handed individuals.
• By contrast, non right-handed individuals show
  more symmetry in the finger representations
  across each hemisphere.
• These differences correspond to fine motor
  performance performed with each hand.

ADM
1mv
Dominant Hemisphere
Non-Dominant Hemisphere
Non-Dominant MEPs
Dominant MEPs
10ms
RESULTS NON RIGHT-HANDED SUBJECT
110
FDI
Dominant Hand
FINGER REPRESENTATIONS NON RIGHT-HANDED
APB
ADM
Dominant Hemisphere
Non-Dominant Hemisphere
Non-Dominant MEPs
Dominant MEPs
ACKNOWLEDGMENTS
The authors thank Jessica Miller for her help in
collecting this data. These experiments were
supported by a grant from the American Heart
Association.
FDI
Non-Dominant Hand
APB
ADM
1mv
10ms