138 CHAPTER 7 Summary This thesis set out to gain understanding of cerebral mechanisms underlying persistent motor dysfunction after peripheral nerve damage in neuralgic amyotrophy (NA), and of how rehabilitation can aid recovery by targeting cerebral processes. The first two chapters provided the necessary Background. Chapter 1 introduced the concept of maladaptive cerebral neuroplasticity and its suspected role in NA and formulated the aims of this thesis. Chapter 2 elaborated on this hypothesis and the research aims, and provided a detailed description of the design, patient population, materials and methods of the subsequent chapters. Part 1 - How the brain adapts to peripheral nerve damage in NA, focused on the question of whether cerebral alterations are involved in patients with NA and residual complaints. We performed two cross-sectional studies that compared cerebral representations of the upper extremity in two separate samples of NA patients to healthy volunteers using a motor imagery paradigm. The behavioural study in chapter 3 formed the foundation for the functional Magnetic Resonance Imaging (fMRI) study described in chapter 4. Part 2 - How rehabilitation can aid recovery in NA, focused on the question of how specific rehabilitation, targeting the central motor system, affects clinical and cerebral outcome in NA. It included two chapters on the NA-CONTROL randomized controlled trial (RCT) comparing specific multidisciplinary outpatient rehabilitation at the Radboudumc Neuromuscular Center to usual care. Chapter 5 described the clinical effects of this rehabilitation, representing most domains of the International Classification of Functioning, Disability and Health (ICF). Chapter 6 described the effects of this rehabilitation on cerebral adaptations in a sub-sample of NA patients, building on the neuroimaging findings of chapter 4. Finally, this chapter 7 provides a summary of the main findings of the chapters in this thesis, followed by a general discussion which places the findings in a broader perspective and provides future directions for research and clinical practice. Part 1 - How the brain adapts to peripheral nerve damage in NA Despite a strong clinical intuition that maladaptive cerebral neuroplasticity plays a role in the persistence of motor dysfunction in NA, this hypothesis had never been tested before the study described in chapter 3. We recruited NA patients with clearly lateralized symptoms of persistent motor dysfunction of the right upper extremity and compared their behavioural performance on a motor imagery task to that of matched healthy volunteers. We selected the hand laterality judgment task, which involves imagined movement of the upper extremity, for its known ability to activate relevant cerebral sensorimotor processes and sensitivity to cerebral alterations in other asymmetrical (nervous system) disorders. We expected to find impaired performance specific to the affected upper extremity in NA patients compared to healthy volunteers. We found that NA patients were specifically less accurate when imagining movements with their affected upper extremity, which indicated that cerebral representations related to the affected upper extremity were indeed altered in NA, confirming our hypothesis. Importantly, NA patients displayed reaction time patterns typical for this task, confirming their reliance on embodied processes. This chapter therefore not only provided the first empirical evidence that cerebral processes were altered in NA patients, it also identified the hand laterality task as a motor imagery tool sensitive to detect cerebral alterations in NA.
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