EEG and Psychometry

It is an old adage in physiology that structure reflects function. In the brain-stem reticular activating system (RAS) there reside three nests of cells making peculiar chemicals known as the biogenic amines, viz. noradrenaline, dopamine and 5-hydroxytryptamine (5HT). What is more, the ramifications of these cells are distributed over the whole extent of the cerebral cortex. What is their function?