[Basal Ganglia and Circuit Function:How Does the Ablation or Deep Brain Stimulation(DBS)Work?]

The basal ganglia(BG)is composed of four parallel loops: the motor, oculomotor, associative, and limbic loops. The motor loop starts from the cortex, travels through the BG and thalamus, and returns to the same area of the cortex with somatotopic organization. The striatum is the major input nucleus of the cortex, and the internal segment of the globus pallidus(GPi)is the main output nucleus. BG is explained by the direct and indirect pathways, and these excitatory or inhibitory pathways are used for several disease models. In Parkinson's disease(PD), dopamine deficiency acts on both direct and indirect pathways to cause the neuronal activity of GPi to becomes disinhibited. Pallidotomy, an effective surgery to improve Parkinsonism, aimed to destroy this hyperactive state. This is based on the rate model. However, a simian PD model with MPTP-treated monkeys exhibited increased GPi activity during effective stimulation of subtalamic nucleus(STN)-DBS, which makes it difficult to explain the pathophysiology of PD based only on the rate model. Instead, the alterative model is now widely prevailing. Local field potentials recorded from the DBS leads implanted in GPi and/or STN uncovered the abnormally synchronized activity in the β range(β oscillation)and abnormal co-synchronization between these nuclei, which is believed to be important in the pathophysiology of PD.