Basal Ganglia Motor Circuit and Physiology of Parkinsonism

기저핵 운동회로와 파킨슨 증상의 신경생리

The basal ganglia are a group of nuclei located in the deep portion of the brain. Along with the cerebellum, the basal ganglia have a major role in controlling human voluntary movements, and their dysfunction is apparently responsible for various involuntary movements. Although the exact mechanism of how the basal ganglia control movements has yet to be clarified, the model of focused selection (through the direct pathway) and tonic inhibition (via the indirect pathway) is proposed to be a principal functional model of the basal ganglia. Parkinson's disease (PD) is classically characterized by bradykinesia, rigidity and tremor-at-rest. All features seem to be associated with dopamine depletion resulting from the degeneration of the nigrostriatal pathway, which produces reduced activity of the direct pathway and a concurrent enhancement of excitatory output from STN. This change may result in increased tonic background inhibition and reduced focused selection via the direct pathway, causing difficulties in performing voluntary movements selectively. However, it has not been possible to define a single underlying pathophysiologic mechanism that explains all parkinsonian symptoms. Here the data that give separate understanding to each of the three classic features are discussed.