Parkinson's disease. Coloured X-ray of a frontal view of the head of a patient with Parkinson's disease, showing electrodes implanted in the brain (centre left). Parkinson's disease is due to degeneration of nerve cells in the basal ganglia of the brain. It causes muscle tremor and a rigid posture in the elderly. Electrodes can be sited in the thalamus region of the brain to provide electrical stimulation of the thalamus. This helps to control the involuntary tremor experienced by Parkinson's sufferers. The electrodes are connected to a battery pack and pulse generator, which are usually sited in the patient's chest (see image M728/032).