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Parkinson’s disease (PD) is a neurodegenerative disorder affecting a variety of brain structures. Its prevalence in the general population is around 0.3% and increases considerably with age (de Lau & Breteler, 2006). The median age of onset is 60 years and the incidence is equal in both sexes (Katzenschlager et al., 2008). While initially symptoms are subtle severe disability often requiring permanent care is present in many patients within a time-frame of about ten years. On the other hand, there are patients who do not show relevant progression of PD over up to ten years (Hoehn & Yahr, 1967). Indeed, the most severe state of PD with regard to the Hoehn and Yahr (H&Y) scale may be reached after 6 to 40 years according to a variety of epidemiological studies (Poewe, 2006). Yet, overall the mortality rate of patients with PD is increased by a factor of 1.5-2.5 compared to the general population (Poewe, 2006). The existence of at least two of the criteria resting tremor, bradykinesia and rigidity in an asymmetrical distribution leads the way to the diagnosis of this movement disorder. Accordingly, the pentamerous unified Parkinson’s disease rating scale (UPDRS) mainly reflects the state of the motor symptoms of PD. Only the first item of the UPDRS takes into account psychiatric symptoms of the disease. However, cognitive decline as well as psychiatric disturbances are common in patients with PD and pose major problems. While the non-motor aspects of PD have been less well studied for a long time, they have received more attention in recent years. Nevertheless, therapy of these symptoms is less advanced compared to the numerous therapeutic options for the motor symptoms of PD. And not infrequently, treatment of motor symptoms and treatment of psychiatric and cognitive aspects of PD interfere with each other. For this chapter the literature on some factors of non-motor aspects of PD has been reviewed and is summarized here.

The ability of the brain to process information relies on its control of the conduction of electric currents. Brain diseases invariably affect this capability. One of the therapeutic approaches to a variety of neurological disorders therefore includes the application of electric currents and fields to the brain. A successful example of this strategy is the introduction of deep brain stimulation which has become a cornerstone of the therapy of advanced Parkinson’s disease (PD), dystonia and essential tremor. Several studies have proven its effectiveness and often patients respond immediately to this therapy. Invasiveness and complexity of this treatment restrict its indication. On the other hand, there are techniques for the non-invasive modulation of cortical excitability namely transcranial magnetic stimulation (TMS) as well as transcranial direct current stimulation (tDCS). These techniques have been investigated in several studies including patients with PD. However results so far are heterogeneous and limit their therapeutic value. In the following chapter the basic principles of as well as therapeutic experiences with invasive and non-invasive electrical stimulation techniques and their applications in patients with PD will be discussed.