Attentional Functions of the Superior Colliculus

The superior colliculus (SC) plays an important role in both overt and covert attention. In primates, the SC is well known to be a central component of the motor pathways that orient the eyes and head to important objects in the environment. Accordingly, neurons in the SC show enhanced responses that will be the target of orienting movements, compared to stimuli that will be ignored. Single-neuron recordings in the SC have revealed a variety of attention-related effects, including changes in activity related to bottom-up and top-down attention, attention capture, and inhibition of return. These findings support the view of the SC as a priority map that represents the location of important objects in the visual environment. Manipulation of SC activity by electrical microstimulation and chemical inactivation shows that the SC is not simply a recipient of attention-related effects, but plays a causal role in these processes. In particular, activity in the SC plays a major role in the selection of targets for saccades, and also for pursuit eye movements and movements of the hand. Moreover, activity in the SC is important not only for the control of overt attention, but also plays a crucial role in covert attention—the processing of visual signals for perceptual judgements even in the absence of orienting movements. The mechanisms mediating the role of the SC in the control of covert attention are not yet known, but current models emphasize interactions between the SC and areas of the cerebral cortex.