Mixed representations of sound and action in the auditory midbrain.

Neurons in IC's superficial "shell" layers preferentially project to higher-order thalamic nuclei that are strongly activated by sounds and their behavioral consequences. This integrative computation is thought critical for a variety of behaviorally relevant functions, such as establishing learned sound valence. However, whether such "mixed representations" reflect unique properties of thalamocortical networks, or rather are inherited from afferent inputs, is unclear. We show that in behaving mice, many shell IC neurons are modulated by sounds and mice's actions. Consequently, shell IC population activity suffices to predict behavioral outcomes even prior to the goal-directed action. Our data thus establish shell IC nuclei as a novel, ascending source of mixed representations for the thalamocortical system.