Hedonic or valence-based learning by valence is inherent to cognition. From a neuroethological perspective, value-assignment requires emotional or volitional characteristics that improve the representation of the environment. Such processing is especially relevant in functions involving episodic memory such as spatial learning, in which navigation may be enhanced by associating states with hedonic values – e.g., the poisonous plant near the river is aversive, and the prey inside a cave is attractive. In this context, dopamine (DA) and serotonin (5-HT) have been studied in their encoding of oppositional valence, whereby DA is driven by positive or appetite-driven rewards and 5-HT acts for negative or aversive stimuli. Both neuromodulators are known to be involved in hippocampal synaptic plasticity and, under certain conditions, DA and 5-HT produce, respectively, long-term potentiation (LTP) and depression (LTD). Here, we examine an antagonistic interplay of these modulators in a navigational model. We compare two reward-modulated spike time-dependent plasticity (R-STDP) learning rules to describe the action of DA and 5-HT. Our results show that modeling the balance between DA and 5-HT as a compensatory mechanism matches the improvement of spatial learning performance observed experimentally in the Morris water maze (MWM) task. We also analyze how the timing assumptions underpinning each rule account for the value description of the environment. Furthermore, this system allows us to predict spatial reversal learning in an open field (OF).