Browsing by Author "Schwarz, Anna"
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Item Persistence or plasticity: examining hand representations subsequent to corticospinal tract lesions and leg representations in transtibial amputees using fMRI(University of Delaware, 2020) Schwarz, AnnaIt has been widely accepted that plastic changes occur after brain damage that are thought to aid in functional and structural recovery. While there is ample evidence that plastic changes do indeed occur after damage, there is also evidence that certain representations within the brain may be preserved and unaffected by plasticity. Changes in cortical maps and functional reorganization in upper limb amputees have been studied. However, research on lower limb amputees is sparse, and it is unknown whether they demonstrate similar plasticity to upper limb amputees. Furthermore, little literature exists on motor representations of paralyzed limbs in stroke patients after subcortical stroke resulting in hemiparesis. Do they change after lack of use over years, or are they maintained even when they are not functionally necessary? We utilized representational similarity analysis (RSA) to examine the nature of limb representations in two transtibial amputees and two corticospinal tract stroke patients with limb hemiparesis. Amputees underwent functional MRI runs in which they were manually stimulated on different segments of their intact and amputated legs, and the stroke patients underwent functional MRI runs in which they were asked to “move” individual digit on either the intact or hemiplegic hand. Amputees did not show greater differentiation in the amputated leg when compared to the intact leg. This means that the representation of the amputated leg is not different than the representation of the intact leg despite evidence for a functional shift of the amputated leg. In one individual with a CST lesion, we found a representation for movement of the hemiplegic hand in contralateral M1 and S1 in a manner consistent with the intact hand, as well as ipsilateral S2 and SMA. CST patient 2 showed representation of the paralyzed hand in ipsilateral M1 and S1. The ability to decode the inter-digit relationships of a hand during “movements” of paralyzed limbs demonstrates that hand representations are preserved in the brain even after years of paralysis.Item PERSISTENCE OR PLASTICITY: EXAMINING HAND REPRESENTATIONS SUBSEQUENT TO CORTICOSPINAL TRACT LESIONS USING FMRI(University of Delaware, 2019-05) Schwarz, AnnaIt has been widely accepted that plastic changes occur after damage to the brain to aid in functional and structural recovery. While there is ample evidence that plastic changes do indeed occur after damage, there is also evidence that certain representations within the brain may be preserved and unaffected by plasticity. Neural correlates of phantom limbs have been studied in depth, but no literature exists on the representations of paralyzed limbs in stroke patients after subcortical stroke resulting in hemiparesis. We utilized Representational Similarity Analysis to compare hand representations in primary motor (M1) and sensorimotor (S1) cortices of subcortical stroke patients to address the extent to which paralyzed hands representations are maintained after years of paralysis. Two patients (n = 2) with lesions to the corticospinal tract and intact motor cortices underwent functional MRI runs in which they were asked to perform individual digit movements on both hands. Functional activity for intact and paralyzed limb movements were then analyzed using RSA to map out hand representations in terms of inter-digit relationships. Paralyzed hand representations in both contralateral M1 and S1were found to be organized in a manner consistent with those of normally working hands. The ability to decode the digit relationships of a hand during “movements” of paralyzed limbs demonstrates that hand representations are preserved in M1 and S1 even after years of paralysis. This facilitates an investigation into the role of peripheral signals in maintaining the function and structure of bodily representations after brain damage.