Place cells, maps and navigation strategies: processing steps of the cortico-hippocampal system

A biologically inspired integrated model of different hippocampal subsystems makes a distinction between place cells (PC) within the entorhinal cortex (EC) (diffuse) or dentate gyrus (segregated), and transition cells (TC) in CA3-CA1 that encode transitions between events. These two types of codes support two kinds of hippocampo-cortical cognitive maps: a context-independent map in the subiculum and EC essentially encodes the spatial layout of the environment thanks to a local dominance of ideothetic movement-related information over allothetic (visual) information, and a task- and temporal context-dependent map based on the TC in CA3-CA1 allows the encoding, in higher-order structures, of maps as graphs resulting from combinations of learned sequences of events. The dominantly spatial and the temporal-task-dependent maps are permanently stored in the parietal cortex and the pre-frontal cortex respectively. On the basis of these two maps, two distinct goal-oriented navigation strategies were designed in experimental robotic paradigms: one based on a (population) vector code of the location-actions pairs to learn and implement to reach the goal, and the other based on linking TC together as conditioning chains that are implemented under the top-down guidance of drives and motivations.