Remarkable effectiveness of deep brain stimulation (DBS) for Parkinson's disease (PD) has occupied the interest of many scientists and their efforts for elucidating its mechanism have given us a lot of clues for understanding of pathophysiology of PD. The early idea that DBS inhibits neuronal activity of the stimulated nucleus was based on the observation that it shows similar effects as lesions, standing behind the so-called firing rate model of PD pathophysiology. However, it has been also revealed that DBS induces changes indicative of activation of outputs from the stimulated structure, which is inconsistent with the firing rate model. On the other hand, recent studies have demonstrated abnormal discharge pattern in the subthalamic nucleus and the globus pallidus of parkinsonian state, such as burst and oscillation, and its suppression by DBS. These support an idea that the pathological discharge interrupts normal information flow in the basal ganglia. Taken together, changes of firing pattern in the basal ganglia may be crucial for the PD pathophysiology, not a simple increase or decrease in firing rates. Besides, since DBS seems to affect the entire system of the basal ganglia and more, it is necessary to approach its mechanism with a systems-wide view.