The effect of lesion size on cortical reorganization in the ipsi and contralesional hemispheres

motrice la plus influencée dans le cortex contralésionnel. ABSTRACT While our understanding of ipsilesional plasticity and its role in recovery of hand function following ischemic stroke has increased dramatically, the reorganization of the contralesional motor cortex and its effect on recovery remain unclear. Currently published studies offer contradictory views on the role of contralesional motor cortex in recovery. Lesion extent has been suggested as the factor determining the type of reorganization of the contralesional motor cortex. The primary goal of this study was thus to evaluate the effect of unilateral strokes of different sizes in caudal forelimb area (CFA) of the rat on both physiological reorganization and behavioral recovery. At the end of a period of spontaneous recovery during which we monitored motor performance of both limbs, we obtained bilateral maps of the CFA and the putative premotor area of the rat – rostral forelimb area (RFA). We found that lesion volume in the CFA correlates with both the extent of behavioral recovery of the paretic hand and the extent of both ipsi and contralesional cortical reorganization. We found that rats with bigger lesions had larger hand representations in the ipsilesional hemisphere and more persistent deficits of the paretic hand. In the contralesional hemisphere we found that rats with larger hand representation in the RFA had bigger lesions and incomplete recovery of the paretic hand. Our results confirm the effect of lesion volume on the reorganization of the contralesional motor cortex and highlight contralesional RFA as the motor cortical area most influenced by lesion volume for future investigations.