Spatial representation versus navigation through hippocampal, prefrontal and ganglio-basal loops

Abstract

A neural network model of intrahippocampal and hippocampo-cortico-gangliobasal loops allows the robotic implementation of the spatial information contained within cognitive maps in neural space, into temporo-spatial sequences of movements during goal-oriented navigation in outer space. At the representation level, the intrahippocampal loop features place cells in entorhinal cortex and transition cells in CA3-CA1 which constitute, as a population, spatial and contextual maps, respectively. Path integration converges with place cell information in the subiculum. The spatial representation in deep and superficial layers of the entorhinal cortex are dissociated; the unidirectional connections between these two layers close the intrahippocamal loop. The prefrontal cortex, at the junction between representation and implementation, receives from three hippocampal subsystems and stores a global graph-map of an environment and the goal locations on this map. The diffusion of activation from active goals through the graph allows path selection in the motivational limbic prefrontal cortex and planning in the executive lateral part. The top-down output from prefrontal cortex and the bottom-up output from the hippocampus combine onto the accumbens the first stage for the stepwise selection and implementation of the optimal actions in the direction of the goal. Proactive and reactive functioning modes are dissociated.