Persistence or plasticity: examining hand representations subsequent to corticospinal tract lesions and leg representations in transtibial amputees using fMRI
Date
2020
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Publisher
University of Delaware
Abstract
It 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.
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Keywords
Amputees, Plasticity, Reorganization, RSA, Stroke