The midbrain origin of auditory predictive processing and how dopamine modulates early perception of surprising sounds

Resumen

The predictive processing framework comprises neurobiologically-informed models of cortical function. These models consist of hierarchical neural networks arranged in several levels of processing. Higher-order levels develop expectations that try to predict and inhibit the input from lower-order levels. In turn, lower-order levels signal prediction errors to higher levels when their expectations about incoming input are not met. The main aim of this thesis is to demonstrate that predictive processing in the auditory system does not begin at the level of the cerebral cortex, but as deep as in the midbrain. Auditory oddball paradigms, in combination with no-repetition controls, were presented to anesthetized rats and awake mice while performing extracellular recordings in the inferior colliculus, in order to find traces of prediction error signaling that could not be accounted for by sheer stimulus-specific adaptation. In addition, dopaminergic agonists and antagonists were applied by means of microiontophoresis in order to test how D2-like receptors mediate the modulation of surprise responses in the neurons of the cortex of the inferior colliculus. Results confirmed that auditory midbrain neurons generate genuine prediction error signals, which expected precision is encoded by dopaminergic projections from the subparafascicular nucleus of the thalamus to the cortex of the inferior colliculus. Hence, the inferior colliculus is the first station capable of implementing predictive processing in the ascending auditory pathway.