Abstract
Neural adaptation enables sensory information to be represented optimally in the brain despite large fluctuations over time in the statistics of the environment. Auditory contrast gain control represents an important example, which is thought to arise primarily from cortical processing. Here we show that neurons in the auditory thalamus and midbrain of mice show robust contrast gain control, and that this is implemented independently of cortical activity. Although neurons at each level exhibit contrast gain control to similar degrees, adaptation time constants become longer at later stages of the processing hierarchy, resulting in progressively more stable representations. We also show that auditory discrimination thresholds in human listeners compensate for changes in contrast, and that the strength of this perceptual adaptation can be predicted from physiological measurements. Contrast adaptation is therefore a robust property of both the subcortical and cortical auditory system and accounts for the short-term adaptability of perceptual judgments.
Highlights
Neural adaptation enables sensory information to be represented optimally in the brain despite large fluctuations over time in the statistics of the environment
We found that level discrimination performance improved when the contrast of the flanking dynamic random chords (DRCs) was low (Fig. 1b), and that this effect was not the result of small contrastdependent differences in overall sound level that are inherent to the DRC stimuli (Supplementary Fig. 1; see Methods)
A Kruskal–Wallis test between contrast gain control in CNIC, MGBv and A1 revealed no significant differences (p = 0.31). These results show that neurons in CNIC, MGBv and A1 substantially compensate for changes in stimulus contrast by adjusting the gain of their input–output relationships
Summary
Neural adaptation enables sensory information to be represented optimally in the brain despite large fluctuations over time in the statistics of the environment. Contrast adaptation may affect multiple neuronal response properties, but is accomplished principally by adjustments in response gain that compensate for the distribution of stimulus levels in a given sensory environment This specific form of contrast adaptation is known as contrast gain control (or contrast normalization). Contrast gain control is a prominent feature of neuronal responses in the auditory cortex of mice[21] and ferrets[9], but in ferrets it is less robust in the midbrain[6] This implies a primary role for auditory cortex in contrast gain control, other studies have shown that the responses of subcortical neurons are influenced by sensory context[22,23,24,25,26,27,28], as well as motor and cognitive demands[29,30,31,32]. We show that the strength of perceptual contrast adaptation in humans can be predicted from the physiological contrast adaptation observed in mouse auditory neurons
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