Notes

Carr, C. E., and M. Konishi. "A circuit for detection of interaural time differences in the brain stem of the barn owl." Journal of Neuroscience 10.10 (1990): 3227-3246. carrCircuitDetectionInteraural

In birds and mammals, spatial hearing relies upon the separation of left and right ears in a binaural auditory system. Comprehending how the brain computes auditory space requires understanding the encoding of interaural time differences (ITDs). The validity of a computational model based on delay lines and coincidence detectors, proposed by Lloyd Jeffress (1948), is here demonstrated in the brain stem of the barn owl. Horseradish injections into the nucleus magnocellularis allowed the tracing of nucleus magnocellularis axons projections onto the nucleus laminaris, showing the nucleus magnocellularis bilateral (ipsilateral and contralateral) afferents to the nucleus laminaris. Intracellular recordings of spikes in the nucleus laminaris were performed under both monaural and binaural acoustic stimuli. These electrophysiological measurements highlighted a maximal response from neurons when phase-locked to a binaural stimulus in which ITD is compensated for by conduction delays. These findings reveal the computational map of the avian nervous system, where delay lines are represented by axons in the nucleus magnocellularis, while neurons in the nucleus laminaris behave as coincidence detectors.
The main contributions introduced by this work are the first demonstration of Jeffress model validity in the animal brain together with a purely systematic computational map of delay lines and coincidence detectors.