Neuroanatomical Correlates of Memory Strategies in Rats

Navigation incorporates a continuum of strategies, where the allocentric strategy relies on relationships between environmental landmarks resulting in a cognitive map, and the egocentric strategy revolves around the body position and stimulus response chains with the body as a reference. Although multiple brain regions contribute to navigation, the hippocampus dominates allocentric navigation, whereas the striatum is key for egocentric navigation. Neuromodulators, such as dopamine and acetylcholine, regulate both the hippocampus and striatum to influence behavior, yet their influence on navigational strategy has not been determined. Interindividual differences in strategy preference are known to exist. Building on these pre-existing interindividual differences, this study explored the neuroanatomical underpinnings on navigational strategy variations in rats through a dual-solution T-maze and immunocytochemistry. Surprisingly, interindividual variations eluded explanation through the density of cholinergic neurons supplying acetylcholine to the hippocampus and striatum. Similarly, the soma morphologies of these neurons exhibited no discernible differences. Dopaminergic cell densities in the ventral tegmental area (VTA), projecting to the hippocampus, and substantia nigra pars compacta (SNpc), projecting to the striatum, failed to account for individual variations as well. Nevertheless, allocentric rats displayed higher VTA/SNpc dopamine neuron fusiformity indexes, potentially contributing to computational distinctions underlying interindividual variations in navigation strategies. This study delves into potential explanations and charts promising avenues for future research. A graphical abstract summarizing the main findings of this study is provided.