This volume of Advances in Anatomy, Embryology and Cell Biol ogy is based on material assembled by Dr. Jaap H.R. Schoen. Dr. Schoen was born in Balikpapan, Indonesia, in 1930 and died in Corsica in 1981 during a diving holiday. Dr. Schoen was a neu rologist at the Diaconessen Ziekenhuis in The Hague, The Neth erlands, and combined his clinical work with a partial tenureship as associated professor in the Department of Neuroanatomy (now the Neuroregulation group) of the Leiden Medical Faculty. For 20 years Dr. Schoen collected pathological specimens from patients with brain disease and together with his technical assistant, Mr. Stins, a large number of Haggqvist, Nauta, and Nissl or Kliiver series were prepared. Little of the studied mate rial has been published. Articles appeared in several journals (Progress in Brain Research, Psychiatria Neurologia, and Neuro chirurgia), but since Dr. Schoen also actively participated in the meetings of the Dutch Anatomical Society, a series of short com munications can be found in the former Acta Morphologica Neer lando-Scandinavica (now the European Journal of Morphology). A list of Schoen's publications has been appended to this preface. Numerous scientists have consulted Schoen's material and, recently, Dr. Jan Voogd published a chapter on the human cere bellum in Paxinos' "The Human Nervous System" (1990) that is based partially on Schoen's material. The Leiden neuroregulation group decided to restore Schoen's material and to publish the manuscripts he left behind."

Part II starts with a systemic model of the basal ganglia to evaluate the position of the STN in the direct, indirect and hyperdirect pathways. A summary of in vitro studies is given, describing STN spontaneous activity as well as responses to depolarizing and hyperpolarizing inputs, and high frequency stimulation. STN bursting activity and the underlying ionic mechanisms are investigated. Deep brain stimulation used for symptomatic treatment of Parkinson s disease is discussed in terms of the elements that are influenced and its hypothesized mechanisms. This part of the monograph pays attention to the pedunculopontine-subthalamic connections and tries in cell cultures to mimic neurotransmitter actions of the pedunculopontine nucleus and high frequency stimulation on cultured dissociated rat subthalamic neurons. STN cell models: single and multi compartment, and system level models are discussed in relation to subthalamic function and dysfunction. Part I and II are mutually compared."

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 virus (HIV) infections. Moreover, the crucial involvement of a lesion of the STN is in doubt (Guridi and Obeso 2001; Postuma and Lang 2003). On the other hand, idiopathic Parkinson's disease (Battistin et al. 1996; Usunoff et al. 2002) is a common neurodegenerative disorder, but the key role of the STN in the pathophysiological origin of the parkinsonian state has become evident only recently (Miller and DeLong 1987; Mitchell et al. 1989; Bergman et al. 1990, 1994; Hollerman and Grace 1992; Guridi et al. 1993; Parent and Hazrati 1995b; Hassani et al. 1996; Levy et al. 1997, 2002; Blandini et al. 2000; Hirsch et al. 2000; Ni et al.