Neural backpropagation

Neural backpropagation is the phenomenon in which the action potential of a neuron creates a voltage spike both at the end of the axon (normal propagation) and back through to the dendritic arbor or dendrites, from which much of the original input current originated. It has been shown that this simple process can be used in a manner similar to the backpropagation algorithm used in multilayer perceptrons, a type of artificial neural network. In addition to active backpropagation of the action potential, there is also passive electrotonic spread. While there is ample evidence to prove the existence of backpropagating action potentials, the function of such action potentials and the extent to which they invade the most distal dendrites remains highly controversial.

When a neuron fires an action potential, it is initiated at the axon initial segment. An action potential spreads down the axon because of the gating properties of voltage-gated sodium channels and voltage-gated potassium channels. Initially, it was thought that an action potential could only travel down the axon in one direction towards the axon terminal where it ultimately signaled the release of neurotransmitters. However, recent research has provided evidence for the existence of backwards propagating action potentials (Staley 2004).

Neural backpropagation can occur in one of two ways. First, during the initiation of an axonal action potential, the cell body, or soma, can become depolarized as well. This depolarization can spread through the cell body towards the dendritic tree where there are voltage-gated sodium channels. The depolarization of these voltage-gated sodium channels can then result in the propagation of a dendritic action potential. Such backpropagation is sometimes referred to as an echo of the forward propagating action potential (Staley 2004). It has also been shown that an action potential initiated in the axon can create a retrograde signal that travels in the opposite direction (Hausser 2000). This impulse travels up the axon eventually causing the cell body to become depolarized, thus triggering the dendritic voltage-gated calcium channels. As described in the first process, the triggering of dendritic voltage-gated calcium channels leads to the propagation of a dendritic action potential.

...
Wikipedia