Professor Benabid's neurology team carries out a computer-aided stereotaxical cranial biopsy. The robot was designed at La Tronche hospital in Grenoble; it helps the surgeon to maximize the instruments trajectory , thanks to 3d technology and NMR and X-ray imaging. Dominique Hoffman, neurosurgeon, Professor Alim-Louis Benabid, head of the neurosurgery department and Professor Jacques Demongeot, head of the medical computer departement, explain how numerization of an atlas of the brain, 3D medical imaging and the linking up of such data could be achieved with the help of mathematicians and programmers. Computer assisted surgery allows for an adventure into waters thus far unchartered.