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Multiple sounds degrade the frequency representation in monkey inferior colliculus
Shawn M Willett1,2, Jennifer M Groh2
1Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
The European Journal of Neuroscience
|November 29, 2021
Summary
Distinguishing simultaneous sounds is challenging. This study found that neural tuning curves in the inferior colliculus broaden, degrading sound representation rather than sharpening it for better discrimination.
Area of Science:
- Neuroscience
- Auditory Perception
- Sensory Processing
Background:
- Distinguishing simultaneous auditory stimuli is complex, especially when neurons respond to overlapping frequencies.
- A hypothesis suggests tuning curve sharpness changes to limit neuronal overlap during simultaneous sound perception.
Purpose of the Study:
- To investigate if changes in neuronal frequency tuning curves in the inferior colliculus aid in distinguishing simultaneous sounds.
- To test the hypothesis that tuning curve sharpening reduces neural overlap for simultaneous sound discrimination.
Main Methods:
- Recorded neuronal activity in the inferior colliculus of monkeys exposed to single and simultaneous sounds of varying frequencies and locations.
- Analyzed frequency selectivity and response function characteristics of neurons during single-sound versus dual-sound trials.
- Utilized a maximum-likelihood decoder to assess the impact of neural changes on sound discrimination performance.
Main Results:
- Monkeys successfully distinguished simultaneous sounds with ~90% accuracy.
- Neuronal frequency selectivity in the inferior colliculus did not sharpen; instead, response functions broadened on dual-sound trials.
- The variance in firing rate explained by frequency decreased, indicating degraded frequency representation during simultaneous sound perception.
- A maximum-likelihood decoder performed worse on dual-sound trials compared to single-sound trials, reflecting the neural changes.
Conclusions:
- The hypothesis that sharpening of frequency tuning curves underlies the perception of simultaneous sounds is not supported.
- Degraded frequency selectivity and broadened neural response functions in the inferior colliculus challenge existing models of auditory perception.
- Alternative mechanisms, like rapid alternations in neuronal firing rates, may explain how the brain distinguishes simultaneous sounds.
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