HIPPOCAMPAL CODE OF AVERSIVE PLACES
Albert M Barth1, Márta Jelitai1, Flóra Vásárhelyi-Nagy1, Ádám Halkó1, Tamás Freund1, Viktor Varga1
1 Institute of Experimental Medicine, Budapest
Past decades of hippocampal research highlighted the fundamental role of hippocampal-entorhinal regions in the spatial coding of physical environment. According to the current theory, ensembles of place cells create spatial representation, a cognitive map of the space around the subject. However, emerging research emphasize that place cells not only code the spatial aspects of the environment but convey non-spatial information too. This hypothesis has gained support by studies demonstrating the coding of non-spatial “spaces” (i.e. frequency fields, odors, tastes) by hippocampal pyramidal cells. Recent data pointed to the existence of hippocampal “reward” cells characterized by preferential firing coupled to reward locations. In contrast, surprisingly little is known about the processing of aversive information in the hippocampus, despite its high translational relevance.In this study our goal was to uncover the hippocampal code of aversive places. We utilized a novel head-fixed experimental arrangement enabling us the simultaneous recording of multiple hippocampal single units while the animal encountered aversive stimuli at certain locations along the movement path. We have observed hippocampal putative pyramidal cells with clear preferential firing around aversive stimulus locations. Moreover, activity of these units reliably followed the stimulus if it was translocated. We have also identified the co-occurrence of place fields and aversive location-coupled firing in a subset of neurons. Importantly, these hippocampal units do not alter their activity upon reward delivery.The above data unravel a pivotal, non-spatial component of the hippocampal map, that may guide behavior in threatening situations.