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 play 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.Significance Statement Navigation relies on the interaction between cognitive demands and motivational context, yet their combined influence on learning dynamics remains poorly understood. Here, we compare how different reward modalities shape the acquisition of a sequential navigation task within a single, controlled environment, while systematically increasing task complexity. We show that reward modality strongly biases early strategy selection under low cognitive demand and continues to modulate learning acquisition as the number of successive choices increase. By isolating reward effects within the same behavioral structure, this work provides an insight to understand how motivation and task complexity jointly shape navigation strategies.