Multiple Running Speed Signals in Medial Entorhinal Cortex

Abstract

Grid cells in medial entorhinal cortex (MEC) can be modeled using oscillatory interference or attractor dynamic mechanisms that perform path integration, a computation requiring information about running direction and speed. The two classes of computational models often use either an oscillatory frequency or a firing rate that increases as a function of running speed. Yet it is currently not known whether these are two manifestations of the same speed signal or dissociable signals with potentially different anatomical substrates. We examined coding of running speed in MEC and identified these two speed signals to be independent of each other within individual neurons. The medial septum (MS) is strongly linked to locomotor behavior and removal of MS input resulted in strengthening of the firing rate speed signal, while decreasing the strength of the oscillatory speed signal. Thus two speed signals are present in MEC that are differentially affected by disrupted MS input.

Principles governing the integration of landmark and self-motion cues in entorhinal cortical codes for navigation

“…This absence of one-to-one correspondence in co-recoded grid and speed cells during gain manipulations raises the important possibility that grid cells integrate input from many speed cells. In line with this idea, several recent works have demonstrated that speed cells show high degrees of heterogeneity, with their firing rates showing positive or negative linear, saturating and even non-monotonic relationships with running speed 7,8,25 . These levels of heterogeneity present a significant challenge for attractor-based grid cell network models, which often require inputs that are positively and linearly modulated by running speed.…”

“…Multiple signals in MEC carry information about running speed, the two most prominent being speed cells 7,8,25 and theta oscillations 7,26 . We first analyzed MEC speed cells, which could provide speed-tuned input to grid cells 8 .…”

“…Border cells increase their firing rate near environmental boundaries, even when these boundaries are represented by visual cues alone 5,6 . Finally, speed cells change their firing rate with the running speed of the animal 7,8 . Thus, as a population, MEC neurons have the capacity to generate an internal map of space, with their codes likely emerging from interactions between self-motion cues, such as locomotion and optic flow, and sensory cues regarding environmental landmarks.…”

Combined Exercise and Cognitive Training System for Dementia Patients: A Randomized Controlled Trial

“…The approach employed and the results obtained in the present study are considered to endorse these previous reports. Furthermore, various previous reports [17][18][19][20][21] have suggested an association between changes in exercise speed and improvement in brain function. These findings suggest that physical training that involves being aware of the focused attention (as adopted in this intervention method) is more likely to lead to higher brain activity and improvement in cognitive function than monotonous physical training.…”

Spatial representation in the hippocampal formation: a history

“…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.…”