1 Introduction 1.1 Hemiballism Hemiballism or hemichorea is a rare neurological disorder, but the crucial invol- ment of the subthalamic nucleus (STN) in its pathophysiology has been app- ciated for decades (Jakob 1923; Martin 1927; Glees and Wall 1946; Whittier and Mettler 1949; Carpenter and Carpenter 1951; Crossman 1987). Only recently have serious doubts come forward. Postuma and Lang (2003) have described the STN as being involved in only a minority of cases, and indicated unrecognized causes such as non-ketotic hyperosmolar hyperglycaemia and complications of human immunodeficiency...

1. 1 Neuro-Electronic Interfacing 1. 1. 1 Nervous System Communication in the(human) bodyand the interaction with the environment is controlled by the nervous system. It can be divided into a central part, which - cludes the spinal cord, brainstem, cerebellum, and cerebrum, and a peripheral part, which includes all neuronal tissue outside the central part (Martini 2001). The latter provides the interface between the central nervous system and the internal and ext- nal environment of the body. Eye, ear, skin, and muscle sensors provide the nec- sary information. Via primary afferent neurons...