Response properties underlying selectivity for the rate of frequency modulated sweeps in the auditory cortex of the...

This study focused on the response properties underlying selectivity for the rate of frequency modulated (FM) sweeps in the auditory cortex of anesthetized C57bl/6 (C57) mice. Linear downward FM sweeps with rates between 0.08 and 20 kHz/ms were tested. We show that at least two different response properties predict FM rate selectivity: sideband inhibition and duration tuning. Sideband inhibition was determined using the two-tone inhibition paradigm in which excitatory and inhibitory tones were presented with different delays. Sideband inhibition was present in the majority (88%, n = 53) of neurons. The spectrotemporal properties of sideband inhibition predicted rate selectivity and exclusion of the sideband from the sweep reduced/eliminated rate tuning. The second property predictive of sweep rate selectivity was duration tuning for tones. Theoretically, if a neuron is selective for the duration that a sweep spends in the excitatory frequency tuning curve, then rate selectivity will ensue. Duration tuning for excitatory tones was present and predicted rate selectivity in ∼34% of neurons (n = 97). Both sideband inhibition and duration tuning predicted rate selectivity equally well, but sideband inhibition was present in a larger percentage of neurons suggesting that it is the dominant mechanism in the C57 mouse auditory cortex. Similar mechanisms shape sweep rate selectivity in the auditory system of bats and mice and movement-velocity selectivity in the visual system, suggesting similar solutions to analogous problems across sensory systems. This study provides baseline data on basic spectrotemporal processing in the C57 strain for elucidation of changes that occur in presbycusis.