In the models discussed in sections 1 – 12, the idea has been that the experimentally recorded electrical activity of neurones, whether fluctuations in membrane potential, spike discharges or some measure of the activity of neural aggregates, is stochastic, and the problem has been to obtain models which generate a stochastic process with properties similar to the observed samples of activity. These models may be abstract, or may contain parameters and variables which correspond to biophysically measurable quantities, and so the models might give insights into possible mechanisms generating the stochastic activity. In this chapter I will consider a different kind of problem: does the stochastic nature of neural activity have any functional implications?