Speed cells in the medial entorhinal cortex

Abstract

Grid cells in the medial entorhinal cortex have spatial firing fields that repeat periodically in a hexagonal pattern. When animals move, activity is translated between grid cells in accordance with the animal's displacement in the environment. For this translation to occur, grid cells must have continuous access to information about instantaneous running speed. However, a powerful entorhinal speed signal has not been identified. Here we show that running speed is represented in the firing rate of a ubiquitous but functionally dedicated population of entorhinal neurons distinct from other cell populations of the local circuit, such as grid, head-direction and border cells. These 'speed cells' are characterized by a context-invariant positive, linear response to running speed, and share with grid cells a prospective bias of ∼50-80 ms. Our observations point to speed cells as a key component of the dynamic representation of self-location in the medial entorhinal cortex.

Spatial representation in the hippocampal formation: a history

“…The coherence of the grid map is particularly strong within ensembles, or modules, of similarly scaled grid cells 154 . A similar degree of coherence is present among head direction cells 6,7,77,78,164 , as well as in the more recently discovered populations of entorhinal border cells and speed cells 165,166 . The coherence of grid cells and head direction cells is state-independent and persists during sleep [167][168][169] .…”

“…In the large majority of speed-tuned MEC cells 166 , firing rates increase linearly as a function of speed, up to 30-40 cm per s in rats. A small but significant number of cells have negative speed-rate relationships 166 . As in the hippocampus, many of these are fast-spiking cells 210 .…”

“…By 2006 it was observed that some information about speed is present in a subset of grid cells, especially in layer III and deeper 187 , but the correlations between firing rate and speed in these cells were weak and would require decoding from large cell numbers to yield a reliable momentary speed signal 166 . We now know that the entorhinal cortex has a distinct population of cells whose firing rates increase linearly with speed 166,209 . In the large majority of speed-tuned MEC cells 166 , firing rates increase linearly as a function of speed, up to 30-40 cm per s in rats.…”

“…We now know that the entorhinal cortex has a distinct population of cells whose firing rates increase linearly with speed 166,209 . In the large majority of speed-tuned MEC cells 166 , firing rates increase linearly as a function of speed, up to 30-40 cm per s in rats. A small but significant number of cells have negative speed-rate relationships 166 .…”

A new direction for grid cells

“…That can be accomplished if the entorhinal cortex has cells sensitive to the speed at which the animal is moving, increasing firing rate with speed of movement, with distance traveled calculated as speed × time. Such "speed cells," as they are called, have recently been discovered in the other Nobel Prize-winning lab (Kropff, Carmichael, Moser & Moser, 2015).…”