As much as a hundred years ago, a quite detailed topographical organization of the brain, and especially of the cerebral cortex, could be deduced from functional deficits and behavioral impairments induced by various kinds of lesion, or by hemorrhages, tumors, or malformations.
Different regions in the brain thereby seemed to be dedicated to specific tasks. One modern systematic technique for causing controllable, reversible simulated lesions is to stimulate a particular site with small electric currents, thereby eventually inducing both excitatory and inhibitory effects and disturbing the assumed local function [75]. If such a spatially confined stimulus then disrupts a specific cognitiveability such as naming of objects, it gives at least some indication that this site is essential to that task.
One straightforward method for locating a response is to record the electric potential or train of neural impulses associated with it. Many detailed mappings, especially from the primary sensory and associative areas of the brain, have been made using various electrophysiological recording techniques.
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⇒ Demonstrations of the Ordering Process