[Theoretical analysis of the multistability of pyramidal neurons]

The two-step switch off the long duration Ca action potential was observed recently in neocortex pyramids [1]. The phenomenon was interpreted as an evidence of the N-type Ca-channel distribution in isolated loci [1]. We demonstrate here that the two-step switch off can be imitated in the model with even channel distribution in a reconstructed pyramidal neuron as well. The first high plateau of the action potential corresponds to steady polarization of the whole membrane. The first switch off of the high plateau to the second low plateau corresponds to the switch off of the steady depolarization of the short basal dendrites. The steady depolarization of the long apical dendrite is more stable thus the switch off of the low plateau is a consequence of the apical dendrite repolarization. The model includes N-channel inactivation and a somatic shunt. The shunt may be artifactual, due to implement, or natural, due to postspike hyperpolarization. Recent experiments [2] have proved that the Ca-channels are located everywhere in the pyramidal cell.