Fig 1.
(A, B) Coronal sections from 2 different animals showing electrolytic lesions (arrows) in the RCIC. Scale bar = 1 mm. Aq, aqueduct; CoIC, commissure of the inferior colliculus; M, medial; PAG, periaqueductal gray; RCIC, rostral cortex of the inferior colliculus; SC, superior colliculus; V, ventral.
Fig 2.
(A) FRA of a neuron in control condition (left panel) and after dopamine application (right panel). (B) The subtraction of the control FRA from the FRA after dopamine application reveals that dopamine increased the excitability of this unit. (C) FRA of another neuron in control condition (left panel) and after dopamine application (right panel). (D) The subtraction of the control FRA from that after dopamine application in (C) reveals that dopamine decreased the excitability of this neuron. The underlying data for this figure can be found in S1 Data. dB SPL, decibels of sound pressure level; FRA, frequency response area
Fig 3.
(A) Scatterplot of the CSI in control condition versus dopamine application. Units that underwent significant CSI changes are represented in purple, whereas the rest are marked as gray dots. The purple cross on the abscissa axis represents 1 CSI measurement in which ordinate value falls out of scale (y = −0.59). (B) Violin plots of the SFR (gray), DEV response (red), and STD response (blue). Control conditions are represented in the left half of each violin (no color), whereas dopamine effects are on display in the right half (colored). Horizontal thick black lines mark the median of each distribution, and vertical bars cover the interquartile range. Regarding statistical significance, n.s. indicates that p > 0.05 and *** indicates that p < 0.001. (C) Scatterplot of DEV responses in control condition versus dopamine application. (D) Scatterplot of STD responses in control condition versus dopamine application. (E) Peristimulus histogram of a unit before (left panel), during (middle panel), and after (right panel) dopamine application. In this case, dopamine reduced the CSI. (F) Another example showing the opposite effects. The underlying data for this Figure can be found in S2 Data. CSI, common stimulus-specific adaptation index; DEV, deviant condition; FR, firing rate; SFR, spontaneous firing rate; STD, standard condition.
Fig 4.
Eticlopride effects on the CSI.
(A) Scatterplot of the CSI in control condition versus eticlopride application. Units that underwent significant CSI changes are represented in green, whereas the rest are marked as gray dots. B. Violin plots of the SFR (gray), DEV response (red), and STD response (blue). Control conditions are represented in the left half of each violin (no color), whereas eticlopride effects are on display in the right half (colored). Horizontal thick black lines mark the median of each distribution, and vertical bars cover the interquartile range. Regarding statistical significance, n.s. indicates that p > 0.05. (C) Scatterplot of DEV responses in control condition versus eticlopride application. (D) Scatterplot of STD responses in control condition versus eticlopride application. (E) Peristimulus histogram of a unit before (left panel), during (middle panel), and after (right panel) eticlopride application. In this case, eticlopride reduced the CSI. (F) Another unit example showing the opposite effects. The underlying data for this figure can be found in S3 Data. CSI, common stimulus-specific adaptation index; DEV, deviant condition; FR, firing rate; SFR, spontaneous firing rate; STD, standard condition.
Fig 5.
Dopamine effects on unexpected auditory input.
(A) Oddball paradigm, displaying 2 experimental conditions for a given fi target tone. (B) CASs highlighting the fi target tone. (C) Scatterplot of the iMM in control condition versus dopamine application. Frequencies that underwent significant iMM changes are represented in purple, whereas the rest are marked as gray dots. (D) Violin plots of the CAS (green), DEV (red), and STD (blue) normalized responses. Control conditions are represented in the left half of each violin (no color), and dopamine effects are on display in the right half (colored). Horizontal thick black lines mark the median of each distribution, and the boxplots inside each distribution indicate the interquartile range, with the confidence interval for the median indicated by the notches. Regarding statistical significance, n.s. indicates that p > 0.05, and ** indicates that p < 0.01 (repeated-measures ANOVA, Dunn–Šidák correction). The underlying data for this figure can be found in S4 Data. CAS, cascade sequence; DEV, deviant condition; FR, firing rate; iMM, index of neuronal mismatch; SFR, spontaneous firing rate; STD, standard condition.
Fig 6.
Schematic diagram of the main connections involved in SSA modulation and PE precision-weighting in the IC. The auditory pathway (in pink) is composed of ascending (solid arrows) and descending connections (dashed arrows) between cortical and subcortical auditory structures. The hierarchical exchange of bottom-up PEs and top-down predictions postulated by the predictive coding framework could be extended to subcortical auditory neurons by means of these feedback loops. The SPF (purple) receives input from main auditory nuclei (pink) and from the mPFC (violet), integrating information from manifold hierarchical processing levels. Such connectivity could allow SPF dopaminergic neurons to estimate the volatility of the probabilistic structure of the auditory context. In turn, the SPF sends dopaminergic projections back to the IC to signal the expected precision of PE signaling at low processing levels. Dopamine release in the nonlemnical IC reduces the postsynaptic responses to surprising stimuli (red) but has no effect on repetitive ones (blue), consequently reducing SSA indices. By contrast, cholinergic modulation from the LDT and PPT nuclei (brown) of the brainstem increases the responses to repetitive stimuli in the IC [65]. Note that the net effect of both dopamine and acetylcholine is the reduction of SSA indices, decreasing the relative saliency of surprising input through complementary means. AC, auditory cortex; CAS, cascade sequence; IC, inferior colliculus; LDT, laterodorsal tegmental; MGB, medial geniculate body; mPFC, medial prefrontal cortex; PE, prediction error; PPT, pedunculopontine tegmental; SOC, superior olivary complex; SPF, subparafascicular nucleus of the thalamus; SSA, stimulus-specific adaptation.