The Introduction gives a brief description of the human cerebral cortex, both in its macroscopic (Fig. E1 — 1) and microscopic features. There is a description of the fundamental units of the nervous system, the neurones or nerve cells, and of their connectivities by means of very intimate contacts called synapses (Fig. E1 — 2). Activation of one type of these synapses excites the neurone and causes it in turn to discharge impulses, which are brief electrical messages travelling along its axon. Activation of the other set of synapses inhibits the neurone and tends to prevent the discharge of impulses. Each neurone has hundreds, or even thousands, of synapses on its surface and discharges impulses only when synaptic excitation is much stronger than inhibition. Impulses are almost the only means of fast transmission in the central nervous system.