The central nervous system (CNS) is specialised in processing information originating from a variety of internal and external sources. Its basic information processing units are nerve cells or neurons. Within the CNS, these elementary building blocks are densely interconnected in hierarchical and parallel pathways. Information originating from sensory neurons in contact with the body periphery is gradually transformed along these pathways to generate specific actions through signals relayed by motor neurons to peripheral organs. Information processing in the CNS exhibits an astonishing degree of diversity when considering the morphology of its neurons, their connectivity patterns, their electrical and their biochemical signalling properties. Thus, the information processing capabilities of animal brains are quite distinct from those of existing man-made machines, being characterised by their resilience to noise, their capacity to rapidly adapt, learn and generalise, as well as their ability to participate in complex social behaviours.