The objective of this study is to better understand the structural and functional changes that the central nervous system (CNS) undergoes following congenital upper limb loss. The focus is on the brain's sensory processing and how neuronal changes may relate to clinical measures. By doing so, the hope is to gain insight into the contribution of critical periods to the plasticity of the sensorimotor processing stream. Both macroscopic and microscopic changes of the brain will be examined in individuals with upper limb amelia and compared to healthy controls. fMRI will be combined with behavioural testing to understand which clinical and behavioural determinants drive somatosensory representations along the entire somatosensory processing stream. Using advanced imaging techniques, the aim is to investigate the contribution of brainstem reorganisation to plasticity observed at the cortical level and, by doing so, gain a better understanding of the mechanistic underpinnings of functional reorganisation. Overall, the hope is to provide the first mechanistic insight into whether early life experiences are crucial for the development of the relay nuclei in the central nervous system and how these changes relate to clinical measures such as adaptive behaviours or pain.