FIGURE 1. Dynamics of action potential initiation in neocortical neurons and in a Hodgkin–Huxley-type model of a neocortical neuron.

a, Action potential in a cat visual cortex neuron in vivo. The arrow shows the characteristic kink at action potential onset. b, Phase plot (dV/dt versus V) of the action potential from a. Inset shows the initial phase of the action potential. c, d, Action potential from a cat visual cortical slice in vitro at 20 °C. e, f, Action potential from a Hodgkin–Huxley-type model of a neocortical neuron⁵.