Universität zu Köln

Wiemer, Valerie Monica ORCID: 0000-0001-5981-2458 (2026). Structural and functional representations of motor network reorganization after stroke. PhD thesis, Universität zu Köln.

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Abstract

Motor control deficits are among the most debilitating consequences of ischemic stroke and pose a significant challenge for rehabilitation and long-term functional independence. Although neuroplastic changes within the brain’s motor network can partially restore motor abilities, the precise mechanisms of reorganization that drive individual differences in recovery remain elusive. This thesis aimed to advance mechanistic insights into how structural network constraints, such as the structural reserve—the premorbid level of structural integrity of pathways unaffected by the lesion—govern functional network reorganization after stroke. To this end, the two studies presented here examined how differences in preserved cortico-cortical structural connectivity (1) relate to basal and complex aspects of upper-limb motor control and (2) guide the adaptive rerouting of motor commands following network reorganization in a population of chronic stroke patients. Study I investigated cortico-cortical structural connectivity as a marker of cortical structural reserve supporting distinct aspects of motor control after stroke. By combining diffusion spectrum imaging with a compartmentwise analytical approach and normative tract templates created from Human Connectome Project data, we quantified tractwise anisotropy between cortical motor regions in chronic stroke patients. Results revealed that basal motor control—defined as simple muscle recruitment—was strongly associated with interhemispheric M1–M1 connectivity, independent of ipsilesional corticospinal tract integrity. In contrast, complex motor control, involving coordinated motor synergies, critically relied on ipsilesional corticospinal fibers and intrahemispheric structural connectivity between ipsilesional M1 and bilateral premotor areas. Therefore, while complex motor control of the paretic upper-limb depended on preserved ipsilesional corticospinal output, basal motor control might be compensated via alternative pathways involving the rerouting of motor commands via contralesional M1 to access intact descending fibers. Extending these findings, Study II examined how individual differences in cortical structural reserve constrain functional network reorganization after stroke. By incorporating dynamic causal modeling of task-related effective connectivity acquired during finger tapping movements alongside the previous structural analyses, this multimodal study assessed structure-function relationships to investigate how cortico-cortical structural connectivity relates to changes in intra- and interhemispheric effective connectivity. When the interhemispheric structural reserve was limited but ipsilesional corticospinal fibers were relatively preserved, motor commands seemed to be preferentially rerouted intrahemispherically via premotor areas, supporting better hand motor control and recovery. Conversely, in patients with low corticospinal integrity and limited intrahemispheric structural reserve, interhemispheric rerouting via contralesional M1 was likely, a pattern associated with poor basal arm motor control and recovery. These results emphasize distinct, structural reserve-dependent rerouting mechanisms underlying motor recovery after stroke. Together, the findings presented in this thesis elucidate the motor task-specific mechanisms of cortical network reorganization after stroke and highlight the pivotal role of individual structural motor network reserve in shaping functional plasticity. Clinically, assessing both CST integrity and broader cortico-cortical connectivity may markedly improve the prediction of motor recovery trajectories and inform personalized rehabilitation strategies, including targeted neuromodulation. Overall, this multimodal framework offers a novel perspective on post-stroke motor recovery and provides crucial insights toward biomarker-driven, individualized therapeutic interventions.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Wiemer, Valerie Monica valerie.wiemer@uk-koeln.de https://orcid.org/0000-0001-5981-2458 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-809656
Date:	2026
Language:	English
Faculty:	Faculty of Medicine
Divisions:	Faculty of Medicine > Neurologie > Klinik und Poliklinik für Neurologie
Subjects:	Medical sciences Medicine
Uncontrolled Keywords:	Keywords Language stroke English structure-function relationships English diffusion MRI English functional MRI English dynamic causal modelling English functional reorganization English
Date of oral exam:	15 July 2026
Referee:	Name Academic Title Kocher, Martin Prof. Dr. Tittgemeyer, Marc Prof. Dr. Ziemann, Ulf Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/80965