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Research Report SRR95-020
Coding of odor intensity in a steady state deterministic model of the olfactory receptor neuron
Jean-Pierre Rospars, Petr Lansky, Henry C. Tuckwell, Arthur Vermeulen
Abstract:
We have studied the coding of odor intensity in a model of an olfactory
receptor neuron
under steady-state stimulation. Our model neuron is an elongated cylinder
consisting of
the following three components: a sensory dendritic region bearing odorant
receptors, a
passive region consisting of proximal dendrite and cell body, and an axon.
Firstly,
analytical solutions are given for the three main physiological responses:
odorant-dependent conductance change at the sensory dendrite based on the
Michaelis-Menten model, generation and spreading of the receptor potential
based on a new
solution of the cable equation, and firing frequency based on a Lapicque model.
Secondly, the magnitudes of these responses are analyzed as a function of
odorant
concentration and their dependence on chemical, electrical and geometrical
parameters are
examined. An `optimal encoder neuron' is presented which suggests that
increasing the
length of the sensory dendrite beyond about 0.3 space constant does not
increase the
magnitude of the receptor potential. Thirdly, the sensivities of the
responses are
examined based on the concentration at half-maximum response, the lower and
upper
concentrations actually discriminated and the distance between them (coding
range). The
maximum conductance at the sensory dendrite appears as the main turning
constant of the
neuron because it determines the shift towards low concentrations and the
increase in
coding range of the receptor-potential response with respect to the
conductance response.
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