the patient's brain; [0031]FIG. 2 is a block diagram illustrating a context in which an implantable neurostimulator according to the invention is implanted and operated, including various items of external equipment; [0032]FIG. 3 is a block diagram illustrating the major functional subsystems of an implantable neurostimulator according to the invention; [0033]FIG. 4 is a block diagram illustrating