Synchronized neurons and sensor-fused rattlesnakes: Using neural synchronization to understand sensory integration and sensory enhancement in rattlesnakes, cats and humans.
National Research Council, U.S. Air Force Research Laboratory
(April 17, 2013 3:00 PM - 3:50 PM)
Sensory integration and sensory binding are similar problems separated by a vast methodological gulf. The dominant paradigm of binding theory is neural synchronization, while sensory integration is built on observations of bimodal neurons. These cells show large increases in firing rates for bimodal presentation of weak stimuli, but little improvement for strong stimuli, a finding known as the Principle of Inverse Enhancement. It would be useful to link these two fields so that methods from each could be used by the other. The best case for such a bridge is the rattlesnake, which has two dissimilar visual systems, one for light and one for heat. Although this sounds like a binding problem, the rattlesnake has been studied using the methods of sensory integration. Many cells in rattlesnake optic tectum are sensitive only to light but can be strongly modulated by heat stimuli, or vice versa. I simulated these cells by assuming that they are members of synchronized pairs of excitatory-coupled rate-coded neurons. I replaced the usual weak coupling assumption with Goldilocks coupling: coupling is kept as strong as possible without distorting spike amplitudes. Both assumptions are unconventional but not unjustifiable. The same synchronized neuron model, without any parameter changes, accounts for a population of cells in cat visual cortex whose firing rates are enhanced by auditory stimuli. It also produces enhancements quite similar to those described psychophysically in humans and could be used to model some human color vision transformations; I present a model of the mysterious enhancement of "yellowness" generated from oscillatory synchronization of known neural mechanisms.