Functional Organisation of the Mouse Superior Colliculus

The superior colliculus (SC) is a highly conserved area of the mammalian midbrain that is widely implicated in the organisation and control of behaviour. SC receives input from a large number of brain areas, and provides outputs to a large number of areas. The convergence and divergence of anatomical connections with different areas and systems provides challenges for understanding how SC contributes to behaviours. Recent work in mouse has provided large anatomical datasets, and a wealth of new data from experiments that identify and manipulate different cells within SC, and its inputs and outputs. These data offer an opportunity to better understand the functional roles of SC. However, some of the observations appear, at first sight, to be contradictory. Here we review this recent work and suggest a simple framework which can capture the observations, and that requires only a small change to previous models. Specifically, the functional organisation of SC can be explained by supposing that three largely distinct circuits support three largely distinct classes of behaviour - arrest, turning towards, and the triggering of escape or pursuit. These behavioural classes are supported by the optic, intermediate and deep layers respectively.