Reward Modality and Task Complexity Shape Learning Dynamics during Multi-decision Sequential Navigation

Learning dynamics depend on internal and contextual multifactors among which the interaction between motivational context and task demands plays an important role. Spatial navigation provides a powerful framework to study these interactions as it integrates cognitive, motivational, and motor components. To examine how reward modality and task complexity modulate learning dynamics in male mice, we used a sequential navigation task in which the number of decision points progressively increased across training, while preserving the same geometrical context and goal location. We compared three versions of the same task, in which the fixed goal location was rewarded by either escape from water (aquatic version), food pellets, or medial forebrain bundle (MFB) stimulation associated with different levels of complexity. At low task complexity, the aquatic group achieved a higher level of performance. However, this effect does not extend to the acquisition of the most complex sequence, as all groups ultimately converge toward comparable abilities to perform direct trials. Furthermore, reward type appears to modulate motivational engagement and speed in all training conditions. Together, these data show that, during spatial navigation, reward modality influences not only the level of learning but also its behavioral execution.