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Abstract

Previous research has linked the contribution of interneuronal networks in the primary motor cortex (M1) to motor planning, preparation and execution. The non-invasive recruitment of distinct networks in M1 can be indexed by measuring motor evoked potentials (MEP) during directional transcranial magnetic stimulation (TMS). Stimulation in the anterior-posterior (AP) direction results in longer latency MEP responses as compared to stimulation in the posterior-anterior (PA) direction. Importantly, corticospinal tract (CST) activation is measured through pulses in the lateral-medial (LM) direction. Variance in response latency is attributed to the synaptic distance between interneurons and the CST neurons. The purposes of this study were 1) to map interneuronal network activation in the contralesional and ipsilesional hemispheres in individuals with chronic stroke (> 6 months) and, 2) characterize the relationship between network activation and motor function post-stroke. Single pulse TMS was delivered bilaterally in the LM, PA and AP directions over the motor cortex in individuals with chronic stroke (n=21). Network onset times were indexed by subtracting mean MEP onset times in the LM direction from the AP and PA directions. The Wolf-Motor Function test (WMFT) quantified arm motor function in both upper limbs (n=20). Results demonstrate a significant difference between AP-LM and PA-LM MEP onset latencies difference in both hemispheres (β = 1.87, CI = 1.29 - 2.45, p