  We present experimental and theoretical arguments, at the single neuron
level, suggesting that neuronal response fluctuations reflect a process that
positions the neuron near a transition point that separates excitable and
unexcitable phases. This view is supported by the dynamical properties of the
system as observed in experiments on isolated cultured cortical neurons, as
well as by a theoretical mapping between the constructs of self organized
criticality and membrane excitability biophysics.
