Towards a model of the emergence of action space maps in the motor cortex

Self-organising maps can recreate many of the essential features of the known functional organisation of primary cortical areas in the mammalian brain. According to such models, cortical maps represent the spatial-temporal structure of sensory and/or motor input patterns registered during the early development of an animal, and this structure is determined by interactions between the neural control architecture, the body morphology, and the environmental context in which the animal develops. We present a minimal model of pseudo-physical interactions between an animat body and its environment, which includes each of these elements, and show how cortical map self-organisation is affected by manipulations to each element in turn. We find that maps robustly self-organise to reveal a homuncular organisation, where nearby body parts tend to be represented by adjacent neurons, but suggest that a homunculus caricature of these maps masks the true organisation as one that remaps from sensory coordinates into `action spaces' for controlling movements of the body to obtain environmental reward. The results motivate a reappraisal of the classic motor cortex homunculus, and demonstrate the utility of an animat modelling approach for investigating the essential constraints that affect cortical map self-organisation.