Progressive increase in grid scale from dorsal to ventral medial entorhinal cortex

Abstract

ABSTRACT:Grid cells are topographically organized in the sense that, within the dorsal part of the medial entorhinal cortex, the scale of the grid increases systematically with anatomical distance from the dorsal border of this brain area. The ventral limit of the spatial map is currently not known. To determine if the grid map extends into the intermediate and ventral parts of the medial entorhinal cortex, we recorded activity from entorhinal principal cells at multiple dorsoventral levels while rats shuttled back and forth on an 18 m long linear track. The recordings spanned a range of more than 3 mm, covering approximately three quarters of the dorsoventral extent of the medial entorhinal cortex. Distinct periodic firing fields were observed at all recording levels. The average interpeak distance between the fields increased from $50 cm in the most dorsal part to $3 m at the most ventral recording positions. The increase in grid scale was accompanied by a decrease in the frequency of theta modulation and the rate of phase precession. The increase in average spacing and field size was approximately linear but this relationship coincided with a substantial increase in the variability of each measure. Taken together, the observations suggest that the spatial scale of the grid representation increases progressively along most of the dorsoventral axis of the medial entorhinal cortex, mirroring the topographical scale expansion observed in place cells in the hippocampus. V V C 2008 Wiley-Liss, Inc.

Grid cell mechanisms and function: Contributions of entorhinal persistent spiking and phase resetting

“…(B) Simulation of a more ventral entorhinal neuron using a smaller value for parameter P(z) 5 0.0048. This results in a smaller shift in persistent spiking frequency (and slower shift in phase) for a given velocity, and results in a larger grid field and a slower shift in firing phase relative to background theta, consistent with experimental data (Brun et al, 2008;Hafting et al, 2008).…”

“…As shown in Giocomo and Hasselmo, 2008a, oscillation data fits the additive version of the model Giocomo and Hasselmo, 2008) and provides the parameter B(z) that accounts for both the scaling of field size and spacing along the dorsal to ventral axis (Giocomo and Hasselmo, 2008a). Simulations of the model (Giocomo and Hasselmo, 2008a) also effectively account for the very large grid cell scale in very ventral regions of medial entorhinal cortex (Solstad et al, 2007;Brun et al, 2008). The simulation of both field size and spacing with the same parameter differs from recurrent attractor models of grid cells that model grid field size with the pattern of synaptic connectivity, but model spacing with the gain of velocity input.…”

“…Similar to the oscillatory interference model , the model of grid cell firing based on persistent firing at stable frequencies can account for theta phase precession, as shown in Figure 3, replicating the theta phase precession of grid cells in entorhinal cortex Layer II . As shown in Figure 3B, the persistent spiking model can also account for precession in the very large grid fields in ventral entorhinal cortex (Solstad et al, 2007;Brun et al, 2008). If one assumes that the theta rhythm oscillations in the entorhinal cortex are determined by the synaptic input arising from the full population, then the stable baseline frequency of the population without any shifts can be assumed to be the reference theta phase.…”

“…Within a local anatomical region, grid cells show the same spacing and orientation, but a range of spatial phases. In contrast, at different positions along the dorsal to ventral axis of medial entorhinal cortex, grid cells show a change in spatial periodicity, with an increase in spacing and field size for grid cells recorded in more ventral regions of medial entorhinal cortex (Hafting et al, 2005;Sargolini et al, 2006;Solstad et al, 2007;Brun et al, 2008;Moser and Moser, 2008).…”

How Animals Find Their Way in Space. Experiments and Modeling

“…Клетки решетки, расположенные рядом, имеют сходные значения шага и ориентации, но могут иметь различные фазы [5]. Шаг решетки постепенно увеличивается в направлении от дорзальной (верхней) стороны энторинальной коры к вентральной (нижней) [5,47]. Изменение шага происходит дискретно, т.е.…”