Abstract
Background/Objective.
We investigated interhemispheric interactions in stroke survivors by
measuring transcranial magnetic stimulation (TMS)–evoked cortical
coherence. We tested the effect of TMS on interhemispheric coherence
during rest and active muscle contraction and compared coherence in
stroke and older adults. We evaluated the relationships between
interhemispheric coherence, paretic motor function, and the ipsilateral
cortical silent period (iSP).
Methods. Participants with (n = 19)
and without (n = 14) chronic stroke either rested or maintained a
contraction of the ipsilateral hand muscle during simultaneous
recordings of evoked responses to TMS of the ipsilesional/nondominant
(i/ndM1) and contralesional/dominant (c/dM1) primary motor cortex with
EEG and in the hand muscle with EMG. We calculated pre- and post-TMS
interhemispheric beta coherence (15-30 Hz) between motor areas in both
conditions and the iSP duration during the active condition.
Results.
During active i/ndM1 TMS, interhemispheric coherence increased
immediately following TMS in controls but not in stroke. Coherence
during active cM1 TMS was greater than iM1 TMS in the stroke group.
Coherence during active iM1 TMS was less in stroke participants and was
negatively associated with measures of paretic arm motor function.
Paretic iSP was longer compared with controls and negatively associated
with clinical measures of manual dexterity. There was no relationship
between coherence and. iSP for either group. No within- or between-group
differences in coherence were observed at rest.
Conclusions.
TMS-evoked cortical coherence during hand muscle activation can index
interhemispheric interactions associated with poststroke motor function
and potentially offer new insights into neural mechanisms influencing
functional recovery.
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