The number of possible "on-off" patterns of neuronal firing is immense, estimated as a staggering ten times ten one million times (ten to the millionth power). The brain is obviously capable of an imponderably huge variety of activity; the fact that it is often organized and functional is quite an accomplishment!

The Developing Mind: How Relationships and the Brain Interact to Shape Who We Are (ed. Guilford Press, 1999) - ISBN: 9781606235799