Subcortical coding of predictable and unsupervised sound-context associations.

Our environment is made of a myriad of stimuli present in combinations often patterned in predictable ways. For example, there is a strong association between where we are and the sounds we hear. Like many environmental patterns, sound-context associations are learned implicitly, in an unsupervised manner, and are highly informative and predictive of normality. Yet, we know little about where and how unsupervised sound-context associations are coded in the brain. Here we measured plasticity in the auditory midbrain of mice living over days in an enriched task-less environment in which entering a context triggered sound with different degrees of predictability. Plasticity in the auditory midbrain, a hub of auditory input and multimodal feedback, developed over days and reflected learning of contextual information in a manner that depended on the predictability of the sound-context association and not on reinforcement. Plasticity manifested as an increase in response gain and tuning shift that correlated with a general increase in neuronal frequency discrimination. Thus, the auditory midbrain is sensitive to unsupervised predictable sound-context associations, revealing a subcortical engagement in the detection of contextual sounds. By increasing frequency resolution, this detection might facilitate the processing of behaviorally relevant foreground information described to occur in cortical auditory structures.