The response of a multisensory neuron in the superior colliculus (SC) to a stimulation of one sensory modality is augmented by the presentation of a stimulus of another sensory modality. Furthermore, the percentage of augment is larger when the unimodal stimuli are weaker. This response property is generally known as multisensory enhancement associated with inverse effectiveness. Although multisensory enhancement has been widely studied experimentally, the mechanism underlying this response remains unclear. We suggest here that, adopting the same strategy as unimodal neurons earlier in sensory pathways, SC multisensory neurons adapt their responses according to the input statistics through processes such as gain control and firing threshold adjustment. We further propose an adaptation rule for the responses of SC multisensory neurons, based on which robust, testable predictions about the role that input statistics may play in multisensory enhancement are produced. Moreover, we suggest that the functional role of cortical afferents from the anterior ectosylvian sulcus (AES) and the rostral aspect of the lateral suprasylvian sulcus (rLS) is to control the overall gain of a SC multisensory neuron based on an estimation of the second-order correlation coefficients between two cross-modal inputs.