LAUSR

Introduction Perinatal stroke (PS) causes most hemiparetic cerebral palsy. Motor recovery is highly dependent on developmental plasticity in bilateral motor cortex. The fundamental neurophysiology of the lesioned motor cortex (M1) is poorly understood. Objective To characterize lesioned corticomotor neurophysiological properties in hemiparetic children with perinatal stroke. Methods Children 6–18 years with MRI-confirmed PS and hemiparesis were recruited (Alberta Perinatal Stroke Project). Transcranial magnetic stimulation (TMS) protocols applied to the lesioned M1 measured rest and active motor thresholds (RMT/AMT) and stimulus response curves (SRC:100-150RMT). Paired-pulse TMS explored short-latency intracortical inhibition and intracortical facilitation (SICI/ICF; 2/10 ms ISI). Measures were compared to the non-lesioned hemisphere and healthy controls (n = 40, median 12.2 years, range 8–18). Motor outcomes by blinded occupational therapists were Assisting Hand (AHA), Melbourne (MA) assessments and Box and Block (BB). Safety and tolerability were assessed. Results Of 45 children (median 11.3 years, 25 male; 65% arterial, 35% PVI), TMS of lesioned M1 evoked contralateral MEPs in only 12 (27%). No ipsilateral MEPs were recorded. Thresholds for evoking a stroke-side MEP were higher than the non-lesioned side (p = 0.04).The s-shaped SRC indicated that the morphology and responsiveness to increases in TMS intensities was preserved but shifted down compared to non-lesioned side or controls contralateral SRC. Contralateral SICI (−39.2%, −42.1%) and ICF (42.5%, 43.6%) effects were comparable between lesioned and non-lesioned sides (p = 0.43, p = 0.54, respectively), as well as controls SICI (p = 0.30) and ICF (p = 0.22). Latencies of MEPs from the lesion side (24.3 ms) were longer than contralateral, non-lesioned MEP (24.3 ms versus 21.6 ms, p = 0.003). The area under the SRC curve is correlated with all AHA (r = 0.9, p = 0.01), MEL (r = 0.9, p = 0.02) and BB (r = 0.8, p = 0.05). Protocols were well tolerated with no adverse events. Conclusion Cortical physiology of contralateral projections from the lesion side can be measured in hemiparetic children with PS using TMS. Individualized neurophysiology will further inform recently demonstrated therapeutic neuromodulation interventions in this population.