New methods for investigation of functional brain changes in response to peripheral damage

Abstract

A recent technique in brachial plexus avulsion is the reconnection of the ending of a broken musculocutaneous nerve to the side of intact phrenic nerve which results in a new double function of the phrenic nerve, allowing it to control both breathing and elbow flexion. It also reconnects the neuronal pathway towards the motor cortex in the brain. However, the mechanism behind this reconnection is not well known, and its physiology is yet to be researched. In this thesis, we investigated the mechanisms underlying the re-establishment of arm function via a doubled arm representation in the primary motor cortex based on functional magnetic resonance imaging (fMRI). After a general introduction, the physical mechanism of MRI/fMRI are introduced. Furthermore, the most essential experimental designs and three technical methods used to explore the reorganization of active brain regions are described. The following section focuses on definitions of brachial plexus avulsion patients, different diagnoses methods and biggest challenges the patients facing. Then we explain experimental details for the fMRI measurement. The next part deals with the analysis of fMRI and data of three technical methods: (i) Dynamic Causal Modeling (DCM), to investigate the effective connectivity, (ii) Diffusion Tensor Imaging (DTI), to investigate the structural connectivity and (iii) Functional Connectivity (FC), to investigate the functional connectivity. fMRI effective/functional connectivity and structural changes within the motor network were compared between a group of patients (6 patients and 12 healthy controls) and age-matched healthy controls (at 7 Tesla). Our results provide the first evidence, that peripheral nervous system reconstruction can evoke complex effective connectivity changes within the motor homunculus of healthy brains and also extend current knowledge about neuroplasticity within the motor cortex. The last part gives a summary of limitations and future research and shows how our new results can contribute to the deep understanding of the disorders.