ABSTRACT
For poorly understood reasons, the dopamine-producing cells in the substantia nigra of patients with Parkinson’s disease die. When patients lose approximately 50% of their dopamine-producing cells, they develop the signs and symptoms of Parkinson’s disease, that is, tremor, rigidity, akinesia (slowness of movements), and postural and gait abnormalities (1). How the dopamine deficiency leads to these signs and symptoms is not fully understood, but it is becoming clear that groups of neurons in the circuits that are deprived of dopamine start behaving abnormally. It is thought that these abnormally firing neurons cause disruption in the cortical and brainstem areas that control movements (2).
