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Rajendran, Anjana

University of British Columbia

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<0.001). A significant interaction between hemisphere and stimulation network was also found (β = -0.84, CI = -1.58 - -010, p = 0.026), with AP-LM MEP onset latency difference being longer in the contralesional hemisphere. The AP-LM MEP onset latency difference between hemispheres explained 21% of the variance in WMFT performance between limbs; this was not the case for PA-LM MEP onset latency differences. Findings suggest the AP-LM onset latency, reflective of CST activation onset times from excitatory transsynaptic inputs, is altered post-stroke, with larger imbalances in AP-LM MEP onset across hemispheres relating to worse motor function after stroke. These data illustrates a new relationship between interneuron pools in the human motor cortex and motor function after stroke.

Text

2024-06-17

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/88474

Neuroscience

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/