13
ʃstim(f)
El

дь
√√Wv
ʊout
Figure 2.1: Circuit diagram of an integrate-and-fire cell. The voltage υ is defined as® ≡ ι⅛ >⅛t∙
Slightly edited from my Master’s thesis (Kellems, 2007).
while v(t) ≤ ½h
Cmυ'(t) = -gL(v(t) - El) + ∕stim(<)M (2∙1)
end
The cell has surface area A and consists of a battery of voltage El, a capacitance
per unit area Cm. and a resistance per unit area gL which defines the leakage current
due to CE ions. This cell is purely passive, meaning that in the absence of input
(i.e., when ∕stimG) = θ) the voltage v will decay back to its resting value v (in this
case V = El). By itself, the ODE in (2.1) does not exhibit spiking behavior, but the
while condition aims to mimic spiking by instantaneously resetting the voltage to v
if v(t) > ½h, at which time the cell is said to have spiked (or fired).
An experimentally-derived single-compartment model that captures spiking be-
havior was introduced in 1952 by Hodgkin and Huxley. Through experiments on the
squid giant axon, they found that the spiking dynamics could be captured through
voltage-gated ionic mechanisms. Specifically, by isolating the Na+ and K+ channels,
they discovered that the flow of ions could be modeled by gating variables that ac-
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