Vallesi, Vanessa (2025). Multimodal MRI of motor impairment and inhibition: Functional connectivity and neurometabolic profiles in spinal cord injury and functional paralysis. (Thesis). Universität Bern, Bern
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Abstract
Spinal cord injury (SCI) disrupts ascending and descending neural pathways, leading to motor and/or sensory dysfunction, with severity depending on lesion height and extent. In functional paralysis (FP), a subtype of functional neurological disorder, similar symptoms occur without yet detectable structural damage. While SCI primarily disrupts spinal signalling, how its supraspinal effects on motor networks evolve from the subacute to chronic phase remains unclear. In FP, symptom generation is presumed to originate from the brain, as suggested by functional neuroimaging studies, yet the underlying mechanism and the meaning of these brain activity alterations remain debated. Additionally, dysfunctional motor inhibitory control, as evidenced by cognitive studies, may further contribute to FP’s pathophysiology. This thesis investigates functional and metabolic correlates of paralysis in SCI and FP using magnetic resonance-based approaches. First, resting-state functional magnetic resonance imaging (fMRI) was used to compare functional connectivity (FC) and spontaneous activity in subacute vs. chronic SCI and healthy controls (HC). Second, fMRI during a motor-inhibition task was used to assess potential differences in the motor-inhibition network between individuals with FP, SCI and HC. Third, proton magnetic resonance spectroscopy was used to compare metabolic profiles in key FP regions among individuals with FP, SCI and HC. Individuals with SCI (both in chronic and subacute phase) exhibited reduced FC in the cerebellar vermis IX, right superior frontal gyrus, and right lateral occipital cortex versus HC. Individuals with chronic SCI showed lower FC in bilateral cerebellar crus I, left precentral gyrus, and middle frontal gyrus than individuals with SCI in the subacute phase and HC, suggesting chronic phase adaptation. Altered spontaneous activity in the left thalamus was unique to individuals with subacute SCI, possibly reflecting early reorganisation. During motor inhibition, both FP and SCI groups showed intact behavioural performance but higher FC in the right precentral gyrus and left insula compared to HC, suggesting compensatory plasticity. Metabolically, both individuals with FP and SCI exhibited lower anterior cingulate total N-acetyl-aspartate to total creatine ratios (tNAA/tCr) compared to HC. As lower tNAA is generally considered a marker of reduced neuronal viability, this finding points to neuronal compromise in both conditions. However, tNAA/tCr correlated significantly with motor strength in SCI but not in FP, suggesting that in FP, the reduction in tNAA/tCr may reflect the presence of paralysis itself rather than its severity. Paralysis alters brain networks, with shared and distinct patterns between SCI phases and between FP and SCI, implying adaptive plasticity. Both conditions showed altered inhibitory network connectivity and reduced anterior cingulate tNAA/tCr, suggesting a relevant contribution of condition-unspecific neural adaptation due to motor dysfunction. Clarifying whether FP-specific functional and metabolic alterations represent mechanistic contributors to symptom generation or reflect non-specific consequences of paralysis will be an important focus for future research.
| Item Type: | Thesis |
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| Dissertation Type: | Cumulative |
| Date of Defense: | 1 September 2025 |
| Subjects: | 600 Technology > 610 Medicine & health |
| Institute / Center: | 04 Faculty of Medicine |
| Depositing User: | Hammer Igor |
| Date Deposited: | 22 Sep 2025 15:29 |
| Last Modified: | 22 Sep 2025 15:29 |
| URI: | https://boristheses.unibe.ch/id/eprint/6725 |
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