TY - JOUR
T1 - Modulation of transcallosal inhibition by bilateral activation of agonist and antagonist proximal arm muscles
AU - Perez, Monica A
AU - Butler, Jane E.
AU - Taylor, Janet L.
PY - 2014/1/15
Y1 - 2014/1/15
N2 - Transcallosal inhibitory interactions between proximal representations in the primary motor cortex remain poorly understood. In this study, we used transcranial magnetic stimulation to examine the ipsilateral silent period (iSP; a measure of transcallosal inhibition) in the biceps and triceps brachii during unilateral and bilateral isometric voluntary contractions. Healthy volunteers performed 10% of maximal isometric voluntary elbow flexion or extension with one arm while the contralateral arm remained at rest or performed 30% of maximal isometric voluntary elbow flexion or extension. The iSP was measured in the arm performing 10% contractions, and electromyographic (EMG) recordings were comparable across conditions. The iSP onset and duration in the biceps and triceps brachii were comparable. In both muscles, the iSP depth and area were increased during bilateral contractions of homologous agonist muscles (extension-extension and flexionflexion) compared with a unilateral contraction, whereas during bilateral contractions of nonhomologous antagonist muscles (extensionflexion and flexion-extension), the iSP depth and area were decreased compared with a unilateral contraction, and sometimes facilitation of EMG was seen. This effect was never observed during bilateral activation of homologous muscles. The size of responses evoked by cervicomedullary electrical stimulation in the arm that made 10% contractions remained unchanged across conditions. Thus transcallosal inhibition targeting triceps and biceps brachii is upregulated by voluntary contraction of the contralateral agonist muscle and downregulated by voluntary contraction of the contralateral antagonist muscle. We speculate that these reciprocal task-dependent interactions between bilateral flexor and extensor arm regions of the motor cortex may contribute to coupling between the arms during motor behavior.
AB - Transcallosal inhibitory interactions between proximal representations in the primary motor cortex remain poorly understood. In this study, we used transcranial magnetic stimulation to examine the ipsilateral silent period (iSP; a measure of transcallosal inhibition) in the biceps and triceps brachii during unilateral and bilateral isometric voluntary contractions. Healthy volunteers performed 10% of maximal isometric voluntary elbow flexion or extension with one arm while the contralateral arm remained at rest or performed 30% of maximal isometric voluntary elbow flexion or extension. The iSP was measured in the arm performing 10% contractions, and electromyographic (EMG) recordings were comparable across conditions. The iSP onset and duration in the biceps and triceps brachii were comparable. In both muscles, the iSP depth and area were increased during bilateral contractions of homologous agonist muscles (extension-extension and flexionflexion) compared with a unilateral contraction, whereas during bilateral contractions of nonhomologous antagonist muscles (extensionflexion and flexion-extension), the iSP depth and area were decreased compared with a unilateral contraction, and sometimes facilitation of EMG was seen. This effect was never observed during bilateral activation of homologous muscles. The size of responses evoked by cervicomedullary electrical stimulation in the arm that made 10% contractions remained unchanged across conditions. Thus transcallosal inhibition targeting triceps and biceps brachii is upregulated by voluntary contraction of the contralateral agonist muscle and downregulated by voluntary contraction of the contralateral antagonist muscle. We speculate that these reciprocal task-dependent interactions between bilateral flexor and extensor arm regions of the motor cortex may contribute to coupling between the arms during motor behavior.
KW - Force
KW - Interhemispheric inhibition
KW - Primary motor cortex
KW - Transcallosal pathways
KW - Transcranial magnetic stimulation
UR - http://www.scopus.com/inward/record.url?scp=84892583006&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84892583006&partnerID=8YFLogxK
U2 - 10.1152/jn.00322.2013
DO - 10.1152/jn.00322.2013
M3 - Article
C2 - 24155008
AN - SCOPUS:84892583006
SN - 0022-3077
VL - 111
SP - 405
EP - 414
JO - Journal of neurophysiology
JF - Journal of neurophysiology
IS - 2
ER -