Fontaine, B. and Brette, R. (2011). Neural development of binaural tuning through Hebbian learning predicts frequency-dependent best delays. J Neurosci 31(32):11692–11696

Abstract. Birds use microsecond differences in the arrival times of the sounds at the two ears to infer the location of a sound source in the horizontal plane. These interaural time differences (ITDs) are encoded by binaural neurons which fire more when the ITD matches their "best delay". In the textbook model of sound localization, the best delays of binaural neurons reflect the differences in axonal delays of their monaural inputs, but recent observations have cast doubts on this classical view because best delays were found to depend on preferred frequency. Here we show that these observations are in fact consistent with the notion that best delays are created by differences in axonal delays, provided ITD tuning is created during development through spike-timing-dependent plasticity: basilar membrane filtering results in correlations between inputs to binaural neurons, which impact the selection of synapses during development, leading to the observed distribution of best delays.

Movie 1. Evolution of the synaptic weights of 3 neurons with CF = 2, 4 and 6, when presented with a binaurally delayed white noise with ITD = 167 µs.

Movie 2. Evolution of the best delays of 160 neurons with CF distributed between 2 kHz and 8 kHz, when presented with uncorrelated binaural noise.

Movie 3. Evolution of the best delays of 160 neurons with CF distributed between 2 kHz and 8 kHz, when presented with natural stereo recordings.