About this Research Topic
A significant proportion of stroke survivors suffers from long-term sensorimotor deficits of the contralesional arm and hand. Neuroimaging, using a diversity of methods, has the potential to uncover underlying principles of functional disabilities and recovery characterizing defined patient groups, including their long term course as well as individual variations. The methods comprise functional MRI measuring task activation as well as resting state. Functional MRI may be complemented by ASL to investigate slowly varying blood flow and associated changes in brain function. For structural MRI robust and accurate computational anatomy methods like voxel-based morphometry and surface based techniques are available. The investigation of the connectivity among brain regions and disruption after stroke is facilitated by DTI. Intra- and interhemispheric coherence may be studied by electromagnetic techniques such as EEG and TMS. In addition, positron emission tomography is capable of imaging specific biological processes.
Consecutive phases of stroke recovery (acute, subacute, early chronic and late chronic stages) are each distinguished by intrinsic processes. Thus, relying alone on the initial deficit and the course of behavioral measures, we are able neither to offer the patient a reliable prognosis in the acute phase nor to determine the end of the recovery process. We do not know the patterns of maximal cortical reorganization as reflected by functional neuroimaging, knowledge which might guide decisions about type and duration of treatment. The site and size of lesions entail partially different functional implications. New strategies to establish functional specificity of a lesion site include calculating contrast images between patients exhibiting a specific disorder and control subjects without the disorder. Large-size lesions often imply poor cerebral blood flow, impeding recovery significantly and possibly interfering with BOLD response. Depending on the site and size of lesion the pattern of recovery will vary. The patterns comprise recovery sensu stricto in the perilesional area, intrinsic compensatory mechanisms using alternative cortical and subcortical pathways, or behavioral compensatory strategies e.g. by using the non-affected limb. In this context, behavioral and neuroimaging measures should be developed and employed to delineate aspects of learning during recovery. Of special interest in stroke recovery is the interplay between sensory and motor areas in the posterior parietal cortex involved in movement planning during reaching and motor hand tasks. Diverse therapeutic interventions should be validated in the light of the physiological processes underlying recovery. And the dominant disability should be characterized, from the level of elementary to hierarchically higher processes such as neglect and motor planning.
In summary, this Research Topic will cover state of the art and new trends in neuroimaging of stroke during recovery from upper limb paresis. Integration of behavioral and neuroimaging findings in probabilistic brain atlases may advance knowledge about stroke recovery. The issue aims to: i. reveal principal physiological mechanisms and long term course of stroke recovery depending on site and size of lesions, ii. correlate specific behavioral and electrophysiological parameters with imaging patterns; iii. delineate neuronal networks involved; and iv. identify sites where treatment methods affect the recovery process.
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