TMS based lower extremity multi-muscle motor mapping in persons post-stroke with impaired muscle coordination

Abstract

Abstract Co-excitation of normally independent muscle groups or modules can explain impaired motor coordination during walking. Mass flexion-extension co-excitation patterns (i.e., only two or three modules instead of the usually observed four modules) are often seen as a consequence of stroke. The corticospinal (CST) and corticoreticular (CRP) networks are major contributors to the production of modules during walking. A structural MRI-based analysis from our lab found that both CST and CRP are involved in locomotor recovery post-stroke and greater involvement of both ipsi- and contralesional CRP is associated with mass flexion-extension synergy leading to a two module pattern and poor walking ability. In the current study, we will further investigate the relationship between a two module pattern and ipsi- and contralesional cortical reorganization with TMS derived motor mapping during standing. Utilizing neuronavigation a 6x8 grid with 1.25 cm between grid points will be centered over individual participants’ T1 image. The motor threshold of the paretic tibialis anterior muscle will be determined during standing (functionally-relevant to walking) with a double-cone coil positioned over the vertex. Ten stimulations at an intensity of 140% of motor threshold will be delivered to each grid point over both hemispheres. Visual feedback will be provided to ensure equal weight distribution between the legs during standing. The average motor evoked potential amplitude and response latency from eight muscles of each leg will be used for motor mapping. We hypothesize that the individuals who have severely damaged CST and two module patterns of walking will have reorganization of leg motor representation in contralesional M1 and/or cortical regions associated with CRP (i.e., supplementary motor area and pre-motor cortex of the ipsi-and-contralesional hemispheres). This ongoing study will provide essential knowledge of the cortical contributions to modules and eventually be applicable to designing patient-specific neuromodulation rehabilitation techniques. Keywords: TMS, motor coordination, gait, Structural MRI