The role of superior colliculus in a logistic decision

Abstract

In many circumstances the brain makes decisions according to logistic classification: summing weighted factors in favor of each option and choosing an option according to a softmax function. Here we find that the superior colliculus (SC) contributes additively to this computation, promoting competing options independently of stimuli. We trained mice to locate an audiovisual stimulus on their left or right, and found that SC encodes the auditory, visual, and action signals in largely separate neurons in different layers. Unilateral SC inactivation did not affect sensory sensitivity but reduced contralateral actions, mostly in favor of inaction. The effects of bilateral inactivation were additive, with balanced inactivations restoring left-right balance. A simple 3-option logistic classification model captured the results, with sensory and prefrontal cortex processing sensory signals and each side of SC additively promoting the contralateral action while slightly opposing the ipsilateral action. The SC thus simultaneously promotes all competing eligible actions.