Short title: Dopamine gates prediction error forwarding in the IC cortices 14 15 Keywords: inferior colliculus (IC), stimulus-specific adaptation (SSA), predictive coding, 16 prediction error, precision, dopamine, auditory 17 18 Highlights 19• Dopamine reduces the responsiveness of IC neurons to unexpected 20 sounds exclusively.
21• Dopamine decreases prediction error forwarding from the IC cortices.
22• Dopaminergic input to the IC cortices encodes precision of prediction 23 errors. 24 Abstract 25 Predictive coding theory describes perception as a hierarchical predictive model 26 of sensation. Higher-level neural structures constrain the processing at lower-27 level structures by suppressing synaptic activity induced by predictable sensory 28 input. But when predictions fail, deviant input is forwarded bottom-up as 29 'prediction error' to update the perceptual model. The earliest prediction error 30 signals identified in the auditory pathway emerge from the cortices of the inferior 31 colliculus (IC). The drive that each prediction error has on the perceptual model 32 depends on its 'precision', which is theoretically encoded by the dopaminergic 33 system. To test it empirically, we recorded single-unit responses from the rat IC 34 cortices to oddball and cascade sequences before, during and after the 35 microiontophoretic application of dopamine or eticlopride (a D2-like receptor 36 antagonist). Thereby, we studied dopaminergic modulation on the subcortical 37 processing of unpredictable and predictable auditory changes. Results 38 demonstrate that dopamine reduces neuronal responsiveness exclusively to 39 unexpected auditory input. High dopamine concentrations in the neuronal 40 microdomain reduce prediction error forwarding via D2-like receptors, without 41 significantly altering repetition suppression. Thus, already at subcortical levels of 42 the auditory pathway, dopaminergic input to the IC gates the bottom-up flow of 43 prediction error signals by encoding their precision.44 45 46 47 48 49 List of abbreviatures 50 CAS: deviant condition. 51 CSI: common SSA index. 52 dB SPL: decibels sound pressure level. 53 DEV: deviant condition. 54 FRA: frequency response area. 55 IC: inferior colliculus. 56 iMM: index of neuronal mismatch. 57 iPE: index of prediction error. 58 iRS: index of repetition suppression. 59 mRNA: messenger RNA 60 PSTH: peristimulus time histogram. 61 SPF: subparafascicular nucleus of the thalamus. 62 SSA: stimulus-specific adaptation. 63 STD: standard condition. 64 TDT: Tucker-Davis Technologies. 65 66 67 68 69 70 71 72Perceptual systems prune redundant sensory input as a means of sparing 73 processing resources while providing saliency to input that is rare, unique, and 74 therefore potentially more informative. This perceptual function has been 75 classically studied in humans using the auditory oddball paradigm (Fig. 1A) [1], 76 where the successive repetition of a tone ('standard condition', henceforth 'STD') 77 is randomly interrupted by an 'oddball' tone ('deviant condition', hence...