Computing with Neural Synchrony
A, Binaural hearing (simplified). The sound arrives at the two ears after a propagation delay dL and dR. Monaural neurons A and B project to a binaural neuron with axonal conduction delays δL and δR. Synchrony (seen on the postsynaptic side) occurs when dR−dL = δL−δR, corresponding to a specific interaural time difference. B, Pitch. Two monaural neurons responding to a sound project to a postsynaptic neuron with axonal delays δA and δB. From the postsynaptic point of view, synchrony occurs for a periodic sound with period 1/f0 matching the delay difference: 1/f0 = δB−δA. C, Olfaction. Left, Odor concentration fluctuates rapidly because of turbulences, and odorant molecules bind to different types of receptors. Each receptor has an odor-specific affinity, so that its coverage by the odor is the product of concentration and affinity. Right, Olfactory neurons A and B have the same receptor type but different global sensitivities, neuron C has a different receptor type. Colored curves schematically represent the sensitivity to different odors, defined as the product of odor affinity and global sensitivity. Synchrony occurs at intersection points, for specific odors. D, More generally, a structured stimulus is described as the image of a lower-dimensional stimulus X through some transformation T. Synchrony occurs in two different neurons when their receptive fields match when combined with the transformation T.