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Interaural phase and level difference sensitivity in low-frequency neurons in the lateral superior olive
1Department of Physiology, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA. Daniel.tollin@uchsc.edu
Summary
Low-frequency sound localization relies on binaural input to the lateral superior olive (LSO). Contrary to prior beliefs, low-frequency LSO neurons in cats are not monaural and exhibit contralateral inhibition, similar to high-frequency neurons.
Area of Science:
- Neuroscience
- Auditory System Research
- Sound Localization Mechanisms
Background:
- The lateral superior olive (LSO) is crucial for encoding interaural level differences (ILDs) for sound localization.
- High-frequency LSO neurons are typically binaural with contralateral inhibition, while low-frequency neurons were traditionally considered monaural.
- Existing anatomical and physiological data suggested low-frequency LSO neurons should also be binaural with contralateral inhibition.
Purpose of the Study:
- To re-examine binaural interaction in low-frequency ( < 3 kHz) lateral superior olive (LSO) neurons.
- To investigate phase locking in the medial nucleus of the trapezoid body (MNTB) for low-frequency sounds.
- To determine if low-frequency LSO neurons exhibit contralateral inhibition.
Main Methods:
- Electrophysiological recordings from low-frequency LSO neurons and MNTB in cats.
- Stimulation with pure tones and noise to assess binaural interactions and phase locking.
- Measurement of neuronal responses to ipsilateral and contralateral auditory stimuli.
- Analysis of sensitivity to interaural time delays (ITDs).
Main Results:
- Phase locking to low-frequency tones was enhanced in the MNTB and low-frequency LSO neurons (<1.2 kHz) compared to the auditory nerve.
- Most low-frequency LSO neurons demonstrated contralateral inhibition, with ipsilaterally driven responses suppressed by contralateral stimuli.
- A majority of neurons were sensitive to ITDs, showing maximal inhibition when stimuli were in-phase across ears.
Conclusions:
- Low-frequency LSO neurons in cats are not monaural, challenging classical descriptions.
- These neurons exhibit contralateral inhibition, mirroring the function of high-frequency LSO neurons.
- The findings support a binaural processing model for low-frequency sound localization in the LSO.
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