We have carried out computational simulations to investigate pharmacological effects in the basal ganglia (BG). Our simulations are based on a computational model, called TELOS, proposed by Brown et al. to explain reactive and planned eye movements. Simulation results demonstrated that dopamine depletion in the BG and the frontal cortex causes delay of eye movements and induces oscillation of the neuronal activity in the BG. We interpret that the occurrence of oscillation in the BG originates mainly from formation of a closed loop circuit due to destruction of dopaminergic neurons in the BG.