Serotonin and dopamine systems: Internal areas and sequential tasks

Serotonin and dopamine transmitters are synthesized in the lower brain but are transmitted widely to many areas of the brain. Emergent representations are critical in understanding their effects. In our prior work [26], their effects on internal, non-motor neurons are studied for pattern recognition tasks only. In this paper, we study their effects on sequential tasks - robot navigation with different settings. They are sequential tasks because the outcome of behavior depends on not only the current behavior as in pattern recognition but also the previous behaviors (e.g., previous navigational trajectories). Analytically, we show that the serotonin and dopamine systems affect the performance of sequential tasks in a compounded way. Experimentally, we show that the effect on the learning rate of feature neurons (in the Y area) allows the agent to approach the friend and avoid the enemy faster as compounding effects of sequential states. Further, we tested the effect of punishment and reward schedule with the same initial locations. We also experimented the effect of punishment and reward schedule with random initial locations. These experiments all indicated that the reinforcement learning via the serotonin and the dopamine systems is beneficial for developing desirable behaviors in this set of sequential tasks - staying close to its friend and away from its enemy. As far as we know, this is the first work that investigates the effects of reinforcer (via serotonin and dopamine) on internal neurons for sequential tasks.