15 GENERAL INTRODUCTION, AIMS & OUTLINE 1 A These hypotheses are tested with motor imagery, task-based functional magnetic resonance imaging of the brain, and a specific multidisciplinary rehabilitation program, which are introduced in the following paragraphs. Motor imagery Motor imagery refers to imagined movement. It shows remarkable similarities to motor execution at the cerebral level: when you imagine performing a movement, your brain activates similar processes and brain regions as when you would actually perform that same movement (see Figure 2). 20-23 Motor imagery typically engages a fronto-parietal network, which is involved in planning and preparing movements. Several key motor areas, such as the supplementary motor area and the premotor cortex, are involved, as are parieto-occipital regions, such as the posterior parietal cortex and the extrastriate body area. 20, 21, 24-26 The more posterior associative areas work together with more frontal somatomotor regions to form sensorimotor representations of your body parts (e.g. the arm), both during motor imagery, motor preparation and motor execution. 26-28 As motor imagery does not involve motor execution, it provides a tool to study sensorimotor representations in the brain, without the influence of peripheral disease factors, such as altered afferent feedback. 29-31 Thus, if NA patients would show altered motor imagery, this would provide evidence that they have altered cerebral processes related to motor control. Task-based functional Magnetic Resonance Imaging32, 33 Magnetic Resonance Imaging (MRI) (Figure 3B) enables us to look inside the human brain and study its organization on several levels. Structural MRI provides an image which shows the structural, or anatomical, organization of the brain with high spatial resolution (see Figure 3A, row 1). With functional MRI (fMRI) it is possible to study the brain’s functional organization, by measuring cerebral activity over time. fMRI measures brain activity based on the principle that brain areas that are more active, require more oxygen and thus greater blood flow, and makes use of the oxygen-carrying haemoglobin’s magnetic Figure 2 Motor imagery Imagining a movement engages similar brain processes as executing that same movement.
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