Hippocampal remapping and grid realignment in entorhinal cortex

Abstract

A fundamental property of many associative memory networks is the ability to decorrelate overlapping input patterns before information is stored. In the hippocampus, this neuronal pattern separation is expressed as the tendency of ensembles of place cells to undergo extensive 'remapping' in response to changes in the sensory or motivational inputs to the hippocampus. Remapping is expressed under some conditions as a change of firing rates in the presence of a stable place code ('rate remapping'), and under other conditions as a complete reorganization of the hippocampal place code in which both place and rate of firing take statistically independent values ('global remapping'). Here we show that the nature of hippocampal remapping can be predicted by ensemble dynamics in place-selective grid cells in the medial entorhinal cortex, one synapse upstream of the hippocampus. Whereas rate remapping is associated with stable grid fields, global remapping is always accompanied by a coordinate shift in the firing vertices of the grid cells. Grid fields of co-localized medial entorhinal cortex cells move and rotate in concert during this realignment. In contrast to the multiple environment-specific representations coded by place cells in the hippocampus, local ensembles of grid cells thus maintain a constant spatial phase structure, allowing position to be represented and updated by the same translation mechanism in all environments encountered by the animal.

Towards a functional organization of the medial temporal lobe memory system: Role of the parahippocampal and medial entorhinal cortical areas

“…For example, the cells shown in Figures 3Bii,iii fired somewhat indiscriminately through different regions of the maze, and although active along the entire central stem, was significantly more active on left-turn and right-turn trials, respectively. In at least some cases, the differences in firing patterns were reminiscent of the shifts in spatial phase and orientation observed when animals move between similarly shaped environments (Fyhn et al, 2007). This pattern of activity was an exclusive feature of MEC neurons, such that we observed no hippocampal units with poorly localized, trial-type specific firing that extended the length of the central stem.…”

“…In particular, the MEC is the location of the grid cells, boundary cells, and head direction cells that reflect different aspects of spatial processing (Sargolini et al, 2006;Moser and Moser, 2008;Solstad et al, unpublished). Notably, the patterns of spatial firing by grid cells in MEC distinguish changes in spatial contexts Fyhn et al, 2007).…”

Grid cells in mice

“…In the hippocampus, 'place cells' have been described in humans (Ekstrom et al, 2003), monkeys (Ono et al, 1991(Ono et al, , 1993Matsumura et al, 1999;Ludvig et al, 2004), bats (Ulanovsky and Moss, 2007), and mice (McHugh et al, 1996;Rotenberg et al, 1996), although it has been proposed that in the monkey hippocampus, discharge is more determined by what the animal sees than where it is (Rolls and O'Mara, 1995;Rolls et al, 1997). Because place cells are likely to be derived from grid cells (O'Keefe and Burgess, 2005;Fuhs and Touretzky, 2006;McNaughton et al, 2006;Solstad et al, 2006;Fyhn et al, 2007), grid cells may exist in a similar range of species. We addressed this question by recording the activity from principal neurons in the medial EC of freely behaving mice.…”

Le codage de l’espace

“…Il s'agit donc d'un codage global de l'espace qui contraste avec la décharge locale de la cellule de lieu [14,15]. Lorsqu'une cellule de grille est enregistrée dans différents environnements, elle maintient la taille et l'espacement du champ, mais l'orientation et la phase de la grille sont modifiées [16]. Cette modification affecte toutes les cellules de grille d'une manière cohérente.…”