In order to understand the cognitive processes, motor actions and the behavioral deficits and neurological disorders rising due to malfunctioning of the related neuronal structures, models at different levels are proposed in computational neuroscience. Models developed considering the nonlinear and distributed working principles of neural structures help to reconstruct the processes but are far away from giving an explicit understanding of the phenomena due to their complexity. However, it is not possible to understand these processes thoroughly with very simple models. To build a relation between these different levels of models and to build a mechanism for understanding these processes, in this work linear model approach is considered. Basal ganglia circuits which are effective in motor action initiation, decision making and action selection is considered and in order to guide through more complex computational models and to understand the working principle, a linear system approach is considered. Though the model proposed is very simple, it gives enough insight to understand the role of basal ganglia circuits and the model is able to show the role of dopamine on modulating the inputs from cortex.