Figure 1  The scheme of intracellular current clamp recordings from a neuron being depolarized by different levels of current injection. As the level of depolarizing current increases (gray levels), the amplitude of subthreshold membrane potential oscillation increases with it. At the moments when the oscillations reach the threshold (dashed line), the neuron generates action potentials (vertical lines represent truncated action potentials). Near the threshold the action potential generation is probabilistic. The number of action potentials (0, 1, 3, 3) increases with the level of depolarization. At the same time, with the increasing current, the phases of action potentials relative to the membrane oscillations advance (left pointing arrows). The range of the phase change is bound to π. Note that while the number of action potentials saturates at 3, the phase still advances. (Scale bar is at bottom left.)