LAUSR

Background. Perinatal stroke causes most hemiparetic cerebral palsy. Ipsilateral connections from nonlesioned hemisphere to affected hand are common. The nonlesioned primary motor cortex (M1) determines function and is a potential therapeutic target but its neurophysiology is poorly understood. Objective. We aimed to characterize the neurophysiological properties of the nonlesioned M1 in children with perinatal stroke and their relationship to clinical function. Methods. Fifty-two participants with hemiparetic cerebral palsy and magnetic resonance imaging–confirmed perinatal stroke and 40 controls aged 8 to 18 years completed the same transcranial magnetic stimulation (TMS) protocol. Single-pulse TMS to nonlesioned M1 determined rest and active motor thresholds (RMT/AMT), motor-evoked potential (MEP) latencies, and stimulus recruitment curves (SRC: 100%-150% RMT). Paired-pulse TMS evaluated short-latency intracortical inhibition (SICI) and intracortical facilitation (ICF). Ipsilateral (IP) participants (ipsilateral MEP ≥0.05 mV in ≥5/20 trials) were compared with contralateral MEP only, nonipsilateral (NI) participants. Assisting Hand and Melbourne assessments quantified clinical function. Results. Twenty-five IP were compared with 13 NI (n = 38, median age 12 years, 66% male). IP had lower motor function. SRC to unaffected hand were comparable between IP and NI while IP had smaller ipsilateral SRC. Ipsilateral MEP latencies were prolonged (23.5 ± 1.8 vs 22.2 ± 1.5 ms contra, P < .001). Contralateral SICI was different between IP (−42%) and NI (−20%). Ipsilateral SICI was reduced (−20%). Contralateral ICF was comparable between groups (+43%) and ipsilaterally (+43%). Measures correlated between contralateral and ipsilateral sides. Conclusion. Neurophysiology of nonlesioned M1 and its relationship to motor function is measureable in children with perinatal stroke. Correlation of excitability and intracortical circuitry measures between contralateral and ipsilateral sides suggests common control mechanisms.