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In a message dated 2/20/99 6:04:57 PM Pacific Standard Time, [log in to unmask] writes: << Finally, the Pallidotomy does Not sever anything: I believe the term used is a'lesion', which I take to mean partial severence of a bundle of nerve fibres in the Pallidus: these form a part of the feedback loop, and I repeat that they are only partially cut. (I am not inventing this- I really believe that that is what is done in the real operation. Maybe someone can check on that?. This is why the patient is conscious- so that the surgeon can tell by the absence of symptoms, when to stop cutting >> Brian, As someone who participated in some of the earlier rounds of this discussion, I'd like to jump back in momentarily to clarify a point. I have had 2 (bilateral) pal's and I double-checked with the surgical team which did my pal's, and I assure you that there IS complete and total cutting of nervous tissue in the globus pallidus, resulting in a break in part of the system involved in the delivery of dopamine and the control of movement. The reason the patient must be conscious during the surgery is to let the surgeon know if they have strayed into dangerous, adjacent areas--eg the optoic nerve tract--while probling to establish the precise lesion site. In this phase of the surgery, the probe does no harm, although it is capable of eliciting excitatory responses when it hits nerve sites--eg when the op[tic nerve tract is stimulated, the patient will see stars and colors when he/she closes his/her eyes. When they have carefully mapped out the lesion site through this method and the use of radio frequency brain mapping, they electrify the probe and zap the site--wholly and fully. The lesion site is actually burned, or cauterized by the electrified probe and the result is that the tissue is dead. At this stage, they don't dare hit adjacent areas, such as the optic nerve tract. The fact that this lesion, microscopic in size, nevertheless causes irreversible brain damage is why DBS is so attractive as an alternative because it does not inflict permanent damage to the tissue. As you implied in your post, it sure is hard to fit the human body, especially the brain, in all of its complexity and subtlety of function and organization into a theoretical model Marty Polonsky.