P28. The functional role of the anterior intraparietal sulcus for recovery of hand function in chronic stroke patients – A combined fMRI-TMS study

Abstract

Introduction After stroke, neuroimaging studies frequently show increased activation of contralesional regions such as the primary motor cortex (M1) and the anterior intraparietal sulcus (aIPS) during movements of the impaired hand ( Rehme et al., 2012 ). There is evidence that these areas may adopt either supportive or disturbing implications for motor control, depending on multiple factors, such as age, stroke severity, and lesion location ( Di Pino et al., 2014 ). Importantly, previous research has mainly focused on investigating this question in the contralesional M1, while other areas involved in motor control, such as the aIPS have often been neglected despite considerable changes in post-stroke activity. Hence, we here examined the role of both ipsi- and contralesional aIPS for recovered motor function in the chronic phase post stroke using neuronavigated ‘online-TMS’ guided by individual fMRI activation maps. Methods First, we assessed structural and functional MRI data of chronic stroke patients and age-matched controls. During fMRI, participants performed an index finger tapping task to localize motor-related activation. The coordinates of peak activity in bilateral aIPS were identified in each participant and subsequently used as stimulation targets to apply short trains of rTMS (10 Hz trains, 90% of resting motor threshold, rMT) time locked to hand movements of different complexity: Participants performed (i) index finger tapping, (ii) pointing between two targets, and (iii) reach-to-grasp movements while ipsilateral M1, aIPS, or contralateral aIPS were transiently disturbed by rTMS. Sham stimulation served as control with the coil being tilted over the parieto-occipital vertex. Task performance was measured using a 3D motion analysis system (Zebris). Results TMS interference with aIPS contralateral to the moving hand led to altered kinematics across all tasks modulating finger tapping amplitudes, pointing accuracy and maximum grip aperture during grasping, highlighting the role of this region for hand motor control in patients and healthy controls. In contrast, interference with aIPS and M1 ipsilateral to the moving hand revealed differential effects in patients. Preliminary data suggest distinct roles of these contralesional areas for recovered hand function in chronic stroke. Conclusions The present findings provide proof-of-principle for the use of fMRI-guided TMS allowing to assess target regions’ functions for hand motor control on the single-subject level. Implementing this approach in a larger cohort of stroke patients provides a promising strategy to individually characterize maladaptive or supportive roles in bilateral aIPS and the contralesional M1 in relation to patient’s motor impairment and lesion topology.