  A fundamental aspect of learning in biological neural networks is the
plasticity property which allows them to modify their configurations during
their lifetime. Hebbian learning is a biologically plausible mechanism for
modeling the plasticity property in artificial neural networks (ANNs), based on
the local interactions of neurons. However, the emergence of a coherent global
learning behavior from local Hebbian plasticity rules is not very well
understood. The goal of this work is to discover interpretable local Hebbian
learning rules that can provide autonomous global learning. To achieve this, we
use a discrete representation to encode the learning rules in a finite search
space. These rules are then used to perform synaptic changes, based on the
local interactions of the neurons. We employ genetic algorithms to optimize
these rules to allow learning on two separate tasks (a foraging and a
prey-predator scenario) in online lifetime learning settings. The resulting
evolved rules converged into a set of well-defined interpretable types, that
are thoroughly discussed. Notably, the performance of these rules, while
adapting the ANNs during the learning tasks, is comparable to that of offline
learning methods such as hill climbing.
