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Neural pathways mediating cross education of human motor function| old_uid | 15570 |
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| title | Neural pathways mediating cross education of human motor function |
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| start_date | 2015/04/30 |
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| schedule | 10h30-12h |
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| online | no |
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| location_info | EuroMov |
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| summary | The potential for significant improvement of upper limb function during the post-acute phase following stroke is often dismissed. Yet it is now well accepted that in older adults – the group most likely to suffer a stroke, there remains the facility for the brain to undergo adaptive change and functional reorganisation. Cross-education is defined as an improvement in the performance of the untrained limb following unilateral training. In a number of recent studies (including randomised controlled trials) that dispel conventional assumptions regarding the utility of this phenomenon in stroke rehabilitation, it has been demonstrated for individuals in the chronic phase of recovery, there is positive transfer of motor skill learning from the healthy limb to the paretic limb. The broad aim of our research program is to establish the manner in which cross education may best be exploited in the service of rehabilitation. While the behavioural expressions of cross-education have been documented thoroughly, the underlying physiological mechanisms remain poorly understood. We have shown previously that (at least in ballistic movement tasks) interlimb transfer of performance is not accompanied by changes in the excitability - as assessed by single-pulse transcranial magnetic stimulation (TMS), of circuits in the primary motor cortex (M1) that innervate corticospinal neurons projecting (via spinal motoneurons) to the muscles of the untrained limb. The acute neural adaptations that mediate bilateral performance gains are however are associated with changes in muscle activation dynamics, of a character that suggests the mediation of brain networks functionally upstream of the elements within M1 that are recruited by single-pulse TMS. Using analyses based on resting-state functional Magnetic Resonance Imaging (rs-fMRI) we obtained evidence that: following training undertaken by the left arm that gave rise to substantial interlimb transfer (and retention) of performance gains, functional connectivity was elevated within the resting motor network - between left and right supplementary motor area (SMA), and between left anterior cingulate cortex (ACC) and right posterior primary motor area (M1p). These changes were not however correlated with or predictive of individual levels of transfer. In the same group of participants, analysis of the Diffusion Weighted Imaging (DWI) data using Constrained Spherical Deconvolution (CSD) based tractography indicated that the apparent fibre density (AFD) of the fibre bundles connecting left and right SMA was negatively correlated with and predictive of the extent of interlimb transfer, both when this was assessed acutely following the training performed by the left limb, and one week later. A replication including only the structural connectivity measures was conducted for a separate group of individuals, wherein AFD in the tracts connecting bilateral SMA was again negatively correlated with and predictive of the degree of interlimb transfer. The findings suggest that, at least for this motor task, interhemispheric interactions between bilateral SMA play an instrumental role in relation to cross education, and that the structural organisation of the intercalating white matter pathways is related to the level of transfer that is realised through unilateral training. |
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| responsibles | Hoffmann, Marin |
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