The brain is the most complex structure in the Universe, and neurologists must puzzle out life-changing diagnoses from the tiniest of clues. In this talk, Suzanne O’Sullivan will follow the trail of her patients’ symptoms: feelings of déjà vu lead us to a damaged hippocampus; spitting and fidgeting to the right temporal lobe; fear of movement to a brain tumour and a missed heartbeat to the limbic system.