““Such networks of neurons are built following the principle that “cells that fire together, wire together” (Hebb’s rule). In short, neurons that are frequently active at the same time tend to become associated and end up connecting with one another. This principle has major implications for brain fitness. First, the more a network of neurons is activated (i.e., the more often the neurons fire together), the stronger the connections become. If a network supporting a brain function is repeatedly stimulated through practice and training, it will become stronger, contributing to the optimization of that brain function. Second, by contrast, the less a network of neurons is activated the weaker the connections become, and weak connections end up dying. This accounts for the popular idea “use it or lose it” – brain functions that are not stimulated end up losing their efficiency since the neural networks supporting them weaken or dissipate.””