**8. Clinical interventions of Parkinson's disease**

Our knowledge and understanding of Parkinson's disease have dramatically increased over the past years, consequently shifting the descriptions of this disease. Parkinson's disease, previously considered to be characterized by only motor symptoms (bradykinesia, rigidity, resting tremor and postural instability), is now viewed as a disease affected by both motor symptoms and a range of non-motor symptoms such as depression, disturbed sleeping patterns, fatigue, hallucination, cognitive impairments, changes in ability to taste or smell and a few other domains. Only during the last couple of decades or so, non-motor related symptoms have begun receiving attention in medical and research communities. As a result, a number of clinical rating tools have been developed to target specific or general non-motor symptoms (Brown et al., 2005; Chaudhuri et al., 2007).

Rigidity is treated as part of parkinsonian motor symptoms. Among the motor symptoms of Parkinson's disease, bradykinesia and rigidity are the signs that are most responsive to medication and surgical treatments. A variety of pharmacological and surgical interventions are available for the management of Parkinson's disease. Levodopa was the first major breakthrough in the treatment of Parkinson's disease, and still remains the "gold standard" in the management of symptoms. Levodopa is converted in the brain into dopamine to replenish the brain's dwindling supply in patients with Parkinson's disease. The introduction of dopamine agonists was a milestone in the treatment of parkinsonian symptoms. In contrast to levodopa, dopamine agonists act directly on dopamine receptors in the brain, and thus can help alleviate the symptoms of Parkinson's disease. Based on preclinical observation, there is an increasingly popular theory known as continuous dopamine agonist stimulation that helps to prevent the occurrence of long-term complications.

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However, with the treatment of medication on advanced stage of this progressive disease, many patients experience motor complications, which is broadly classified as "wearing off reactions", "On-Off reactions", dyskinesia, confusion, sleepiness, hallucination, and low blood pressure when standing (Stacy, 2009). In patients who are severely affected or in those who fail to respond satisfactorily to pharmacological therapy, surgical treatments have reportedly been effective in reducing symptoms and improving function. These include pallidotomy, thalamotomy and subthalamotomy, and high frequency deep brain stimulation via electrodes implanted in the globus pallidus, thalamus (a "relay station" deep in brain), or subthalamic nucleus. Rigidity can be specifically improved by subthalamic nucleus deep brain stimulation (Temperli et al., 2003).
