"One of the oldest and still most important techniques for studying neurons in aggregate is to destroy all of the cells in one small region of the brain and then to observe how brain operation is altered as a result of the lesion. Lesion is used as a noun to indicate the area of destroyed cells and also as a verb to denote the act of destroying cells; From the nature of the change in brain function, together with other types of evidence, it is often possible to assign a role in nervous system operation to neurons in the area destroyed. Quite frequently, some function of the brain will be lost completely: for example the animal may be blind, or deaf, or unable to move a limb after the brain area has been destroyed. In such cases of a deficit following the loss of cells in a specific area, it is usually inferred that those cells were intimately involved in performing the lost function. Some lesions do not cause deficits, but rather result in exaggerated performance of some operation. For example, destruction of cells in a particular area of the hypothalamus leads to almost continuous eating and to enormous increases in body weight. Such an increase in a type of behavior is known as a release phenomenon, and is taken to indicate that the cells which were destroyed normally serve to inhibit other neurons responsible for the behavior which has become exaggerated. " (C.F. Stevens, 1966)
Stevens, C. F. 1966. Neurophysiology: a primer. John Wiley and Sons, New York.