Figure 9.2 Single ion channels in a membrane opening and closing. (Courtesy of P. Adams.)

the cell's firing that active synapses would otherwise cause. Adams and his colleagues have shown that many of these calcium and potassium channels are regulated by "neuromodulators," chemicals released by active synapses.

Working energetically from the bottom up, "the cellular or molecular neurobiologist may appear to be preoccupied by irrelevant details" that shed no light on high-level functions, Adams conceded. "Knowing the composition of the varnish on a Stradivarius is irrelevant to the beauty of a chaconne that is played with it. Nevertheless," he asserted, "it is clear that unless such details are just right, disaster will ensue." Any more global theory of the brain or the higher or emergent functions it expresses must encompass theories that capture these lower-level processes. Adams concluded by giving "our current view of the brain" as seen from the perspective of an experimental biophysicist: ''a massively parallel analog electrochemical computer, implementing algorithms through biophysical processes at the ion-channel level.''

The complexity of the brain's structure and its neurochemical firing could well stop a neural net modeler in his or her tracks. If the