Parkinson's disease: the syndrome, the pathogenesis and pathophysiology.

Parkinson's disease (PD) is characterised by a slowly expanding degeneration of neurons particularly in the mesencephalon. The causes are unknown although risk factors in the genetic and toxic domain are being discovered. An important pathophysiological feature in PD is the loss of part of the dopaminergic neurons in the substantia nigra (SN) resulting in a specific dysorganisation of the complicated basal ganglia (BG) circuits. The relay functions at the level of the striatum e.g., are out of balance leading to disturbed subcortico-cortical interactions. At a functional level this is shown by timing and scaling problems when performing movements and clinically this translates into initiation problems, bradykinesia and others. Dysarthria can of course be an important problem. However, how these basic disturbances of motor organisation can be copied into the cognitive domain (in terms of disturbed "mental movements") is a topic under discussion. It remains to be seen whether the basic pathophysiology of PD has consequences for the specific language organisation by the brain or whether language problems are merely secondary to the overall "mental motor slowing". Here an overview of the pathogenesis, basic pathophysiology and clinical problems of PD will be given.