Linear summation in the barn owl's brainstem underlies responses to interaural time differences

Area of Science:

• Neuroscience
• Auditory System Research
• Computational Neuroscience

Background:

• The neurophonic potential is an extracellular field potential recorded in the barn owl's nucleus laminaris (NL).
• Its generators are debated, with potential sources including afferent axons, synapses, and NL neuron spikes.

Purpose of the Study:

• To determine the primary generators of the neurophonic potential in the nucleus laminaris.
• To investigate whether binaural neurophonic responses can be predicted by the sum of monaural inputs.

Main Methods:

• Experimental recording of neurophonic potentials in barn owls.
• Application of a linear summation model to predict binaural responses from monaural stimulation data.
• Comparison of model predictions with experimental data for varying interaural time differences.

Main Results:

• The neurophonic potential primarily reflects inputs (afferent axons and synaptic potentials) to the NL, not its outputs (neuron spikes).
• A linear summation model accurately predicted binaural neurophonic responses based on monaural stimulation.
• Model predictions showed an excellent fit with experimental data, even without considering NL neuron nonlinearities.

Conclusions:

• Afferent axons and their synaptic potentials are the predominant generators of the neurophonic potential in the nucleus laminaris.
• The convergence of monaural inputs in NL creates a binaural neurophonic whose responses are linearly summable.
• These findings support the input-driven origin of the neurophonic potential, independent of the complex nonlinear processing by NL coincidence detector neurons.