According to the abovementioned notes, we suggest adding the effects of tonic level change as another reward parameter in the Actor–Critic model in Parkinson’s disease. It must be noted that the phasic level-based models do not support the experimental results appropriately during dual tasks. For example, it is seen that in dual-task experiments, correcting the phasic level of dopamine did not improve the decision-making process. In dual-task conditions, when a small change in tonic level happens, a big failure occurs during the decision-making process. This would confirm that adding tonic level to the model improve its validity in accordance with human experimental results. Applying this idea, we would be able to consider how the decision-making process is affected by mental tasks such as cognitive functions in Parkinson’s disease; however, appropriate experiments are needed to study this suggestion and to validate it.