The value of electrostimulation in epileptic focus localization

The ES is a non-physiological stimulus of the brain. However it represents an important and indispensable part of stero-EEG investigation since it is an easily adjustable method, capable of inducing typical electro-clinical seizures. From the clinical and electrical responses elicited by ES and from the data of the stimulation tresh-old, we are in agreement with other authors, we feel we can also distinguish several different reacting zones in the epileptic brain: 1. The epileptogenic zone from which the complete or almost complete electro-clinical seizure is reproducible immediately by ES or with short latency. These pathological responses show the severe dysfunction of the given structures. 2. The irritative zones from which seizure elements can be evoked, but the complete electro-clinical seizure does not. "Physiological" clinical responses can also be elicited, but by a very low threshold stimulus pointing to the pathological excitability of this zone. 3. The area reacting to "normal" stimulus threshold with a physiological response. 4. The silent area without any electro-clinical response in the functional state of the nervous system. One of the practical values of ES is that makes possible to separate these zones from each other in a given patient within certain limits, and it may help to reveal the localization, the multiplicity and the degree of the "seizure disposition" in epilepsy.