Depolarization block in olfactory sensory neurons expands the dimensionality of odor encoding

Upon strong and prolonged excitation, neurons can undergo a silent state
called depolarization block that is often associated with disorders such
as epileptic seizures. Here we show that neurons in the peripheral
olfactory system undergo depolarization block as part of their normal
physiological function. Typically, olfactory sensory neurons enter
depolarization block at odor concentrations three orders of magnitude
above their detection threshold, thereby defining receptive fields over
concentration bands. The silencing of high-affinity olfactory sensory
neurons produces sparser peripheral odor representations at high-odor
concentrations, which might facilitate perceptual discrimination. Using a
conductance-based model of the olfactory transduction cascade paired with
spike generation, we provide numerical and experimental evidence that
depolarization block arises from the slow inactivation of sodium channels
— a process that could affect a variety of sensory neurons. The existence
of ethologically-relevant depolarization block in olfactory sensory
neurons creates a new dimension that expands the peripheral encoding of
odors.