TY - JOUR
T1 - Paradoxical facilitation alongside interhemispheric inhibition
AU - BELYK, MICHEL
AU - Banks, Russell
AU - Tendera, Anna
AU - Chen, Robert
AU - Beal, Deryk S
N1 - Funding Information:
This work was funded by grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Kimmel Family Opportunity Fund to M.B., and the Ward Family Summer Student Research Program to the lab of D.B.
Publisher Copyright:
© 2021, The Author(s).
PY - 2021/11/1
Y1 - 2021/11/1
N2 - Neurophysiological experiments using transcranial magnetic stimulation (TMS) have sought to probe the function of the motor division of the corpus callosum. Primary motor cortex sends projections via the corpus callosum with a net inhibitory influence on the homologous region of the opposite hemisphere. Interhemispheric inhibition (IHI) experiments probe this inhibitory pathway. A test stimulus (TS) delivered to the motor cortex in one hemisphere elicits motor evoked potentials (MEPs) in a target muscle, while a conditioning stimulus (CS) applied to the homologous region of the opposite hemisphere modulates the effect of the TS. We predicted that large CS MEPs would be associated with increased IHI since they should be a reliable index of how effectively contralateral motor cortex was stimulated and therefore of the magnitude of interhemispheric inhibition. However, we observed a strong tendency for larger CS MEPs to be associated with reduced interhemispheric inhibition which in the extreme lead to a net effect of facilitation. This surprising effect was large, systematic, and observed in nearly all participants. We outline several hypotheses for mechanisms which may underlie this phenomenon to guide future research.
AB - Neurophysiological experiments using transcranial magnetic stimulation (TMS) have sought to probe the function of the motor division of the corpus callosum. Primary motor cortex sends projections via the corpus callosum with a net inhibitory influence on the homologous region of the opposite hemisphere. Interhemispheric inhibition (IHI) experiments probe this inhibitory pathway. A test stimulus (TS) delivered to the motor cortex in one hemisphere elicits motor evoked potentials (MEPs) in a target muscle, while a conditioning stimulus (CS) applied to the homologous region of the opposite hemisphere modulates the effect of the TS. We predicted that large CS MEPs would be associated with increased IHI since they should be a reliable index of how effectively contralateral motor cortex was stimulated and therefore of the magnitude of interhemispheric inhibition. However, we observed a strong tendency for larger CS MEPs to be associated with reduced interhemispheric inhibition which in the extreme lead to a net effect of facilitation. This surprising effect was large, systematic, and observed in nearly all participants. We outline several hypotheses for mechanisms which may underlie this phenomenon to guide future research.
KW - Transcranial magnetic stimulation
KW - Interhemispheric inhibition
KW - Corpus callosum
KW - Experimental design
KW - Optimization
KW - Facilitation
UR - http://dx.doi.org/10.1007/s00221-021-06183-9
UR - http://www.scopus.com/inward/record.url?scp=85114106734&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85114106734&partnerID=8YFLogxK
U2 - 10.1007/s00221-021-06183-9
DO - 10.1007/s00221-021-06183-9
M3 - Article (journal)
C2 - 34476535
SN - 0014-4819
VL - 239
SP - 3303
EP - 3313
JO - Experimental Brain Research
JF - Experimental Brain Research
IS - 11
ER -