Grid cells require excitatory drive from the hippocampus
TL;DR: The results point to excitatory drive from the hippocampus, and possibly other regions, as one prerequisite for the formation and translocation of grid patterns in the MEC.
Abstract: Previous evidence has suggested that hippocampal place fields in rodents arise from the summation of input from entorhinal grid cells. Here the authors show that perturbing excitatory backprojections from the hippocampus to the entorhinal cortex causes a gradual firing rate–dependent loss of grid pattern and an emergence of head-directional tuning in grid cells of the medial entorhinal cortex.
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TL;DR: It is argued that entorhinal grid cells encode a low-dimensionality basis set for the predictive representation, useful for suppressing noise in predictions and extracting multiscale structure for hierarchical planning.
Abstract: The authors show how predictive representations are useful for maximizing future reward, particularly in spatial domains. They develop a predictive-map model of hippocampal place cells and entorhinal grid cells that captures a wide variety of effects from human and rodent literature. A cognitive map has long been the dominant metaphor for hippocampal function, embracing the idea that place cells encode a geometric representation of space. However, evidence for predictive coding, reward sensitivity and policy dependence in place cells suggests that the representation is not purely spatial. We approach this puzzle from a reinforcement learning perspective: what kind of spatial representation is most useful for maximizing future reward? We show that the answer takes the form of a predictive representation. This representation captures many aspects of place cell responses that fall outside the traditional view of a cognitive map. Furthermore, we argue that entorhinal grid cells encode a low-dimensionality basis set for the predictive representation, useful for suppressing noise in predictions and extracting multiscale structure for hierarchical planning.
616 citations
TL;DR: Virtual reality is used to dissociate visual environmental from physical motion inputs, while recording place and grid cells in mice navigating virtual open arenas to show that place cells predominantly encode environmental sensory input, while grid cell activity reflects a greater influence of physical motion.
Abstract: Place and grid cells in the hippocampal formation provide foundational representations of environmental location, and potentially of locations within conceptual spaces. Some accounts predict that environmental sensory information and self-motion are encoded in complementary representations, while other models suggest that both features combine to produce a single coherent representation. Here, we use virtual reality to dissociate visual environmental from physical motion inputs, while recording place and grid cells in mice navigating virtual open arenas. Place cell firing patterns predominantly reflect visual inputs, while grid cell activity reflects a greater influence of physical motion. Thus, even when recorded simultaneously, place and grid cell firing patterns differentially reflect environmental information (or ‘states’) and physical self-motion (or ‘transitions’), and need not be mutually coherent. Place cells and grid cells are known to encode spatial information about an animal’s location relative to the surrounding environment. Here, the authors show that place cells predominantly encode environmental sensory inputs, while grid cell activity reflects a greater influence of physical motion.
588 citations
01 Jan 1976
TL;DR: The death rate per tumor cell due to immunological response is proportional to the total number of antigen-producing (tumor) cells; thus, the total death rate is quadratic.
Abstract: Let X(t) be the number of tumor cells at time t, and Pr{X(t) = n} = pn(t) is the density of X. A “birth”, i.e., an increase of one of the total population of cancer cells, can occur either by mutation of a normal cell caused by the action of the carcinogen, consisting of randomly (Poisson) distributed hits, or by reproduction of existing cancer cells. A death of a tumor cell occurs as an additive combination of non-immunological and immunological elements. Once a tumor is initiated by carcinogenic action, it undergoes a birth and death process with infinitesimal birth rate linear and infinitesimal death rate composed of a linear and a nonlinear term, the former due to non-immunological deaths, the latter to immunological feedback. The death rate per tumor cell due to immunological response is proportional to the total number of antigen-producing (tumor) cells; thus, the total death rate is quadratic. Although this assumes a very simple mechanism for the action of immunological feedback, it is nevertheless a first step.
565 citations
TL;DR: It is argued that the neuroscience of spatial cognition is emerging as an exceptionally integrative field which provides an ideal test-bed for theories linking neural coding, learning, memory and cognition.
Abstract: Over the past four decades, research has revealed that cells in the hippocampal formation provide an exquisitely detailed representation of an animal's current location and heading. These findings have provided the foundations for a growing understanding of the mechanisms of spatial cognition in mammals, including humans. We describe the key properties of the major categories of spatial cells: place cells, head direction cells, grid cells and boundary cells, each of which has a characteristic firing pattern that encodes spatial parameters relating to the animal's current position and orientation. These properties also include the theta oscillation, which appears to play a functional role in the representation and processing of spatial information. Reviewing recent work, we identify some themes of current research and introduce approaches to computational modelling that have helped to bridge the different levels of description at which these mechanisms have been investigated. These range from the level of molecular biology and genetics to the behaviour and brain activity of entire organisms. We argue that the neuroscience of spatial cognition is emerging as an exceptionally integrative field which provides an ideal test-bed for theories linking neural coding, learning, memory and cognition.
422 citations
Cites background from "Grid cells require excitatory drive..."
...Interestingly, inactivation of the hippocampus also makes grid cells lose their gridness [150]....
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TL;DR: Direct, quantitative evidence is presented that CA3 produces an output pattern closer to the originally stored representation than its degraded input patterns from the dentate gyrus (DG) when local and global reference frames were placed in conflict.
401 citations
Cites background from "Grid cells require excitatory drive..."
...Neurosci. conference); and (4) inactivation of hippocampal place cells can cause the loss of gridness in MEC cells (Bonnevie et al., 2013)....
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...conference); and (4) inactivation of hippocampal place cells can cause the loss of gridness in MEC cells (Bonnevie et al., 2013)....
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References
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TL;DR: Preliminary observations on the behaviour of hippocampusal units in the freely moving rat provide support for this theory of hippocampal function.
5,549 citations
"Grid cells require excitatory drive..." refers methods in this paper
...The simulation then consisted of integrating equation (1) with a 1-ms time step over 10-min paths taken from the experiments....
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...Grid scores and mean vector lengths were calculated from the rates found by simulating equation (1) and the definition used in the experimental analysis....
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TL;DR: The dorsocaudal medial entorhinal cortex (dMEC) contains a directionally oriented, topographically organized neural map of the spatial environment, whose key unit is the ‘grid cell’, which is activated whenever the animal's position coincides with any vertex of a regular grid of equilateral triangles spanning the surface of the environment.
Abstract: The ability to find one's way depends on neural algorithms that integrate information about place, distance and direction, but the implementation of these operations in cortical microcircuits is poorly understood. Here we show that the dorsocaudal medial entorhinal cortex (dMEC) contains a directionally oriented, topographically organized neural map of the spatial environment. Its key unit is the 'grid cell', which is activated whenever the animal's position coincides with any vertex of a regular grid of equilateral triangles spanning the surface of the environment. Grids of neighbouring cells share a common orientation and spacing, but their vertex locations (their phases) differ. The spacing and size of individual fields increase from dorsal to ventral dMEC. The map is anchored to external landmarks, but persists in their absence, suggesting that grid cells may be part of a generalized, path-integration-based map of the spatial environment.
3,445 citations
TL;DR: The phase was highly correlated with spatial location and less well correlated with temporal aspects of behavior, such as the time after place field entry, and the characteristics of the phase shift constrain the models that define the construction of place fields.
Abstract: Many complex spike cells in the hippocampus of the freely moving rat have as their primary correlate the animal's location in an environment (place cells). In contrast, the hippocampal electroencephalograph theta pattern of rhythmical waves (7-12 Hz) is better correlated with a class of movements that change the rat's location in an environment. During movement through the place field, the complex spike cells often fire in a bursting pattern with an interburst frequency in the same range as the concurrent electroencephalograph theta. The present study examined the phase of the theta wave at which the place cells fired. It was found that firing consistently began at a particular phase as the rat entered the field but then shifted in a systematic way during traversal of the field, moving progressively forward on each theta cycle. This precession of the phase ranged from 100 degrees to 355 degrees in different cells. The effect appeared to be due to the fact that individual cells had a higher interburst rate than the theta frequency. The phase was highly correlated with spatial location and less well correlated with temporal aspects of behavior, such as the time after place field entry. These results have implications for several aspects of hippocampal function. First, by using the phase relationship as well as the firing rate, place cells can improve the accuracy of place coding. Second, the characteristics of the phase shift constrain the models that define the construction of place fields. Third, the results restrict the temporal and spatial circumstances under which synapses in the hippocampus could be modified.
2,434 citations
TL;DR: Theoretical studies suggest that the medial entorhinal cortex might perform some of the essential underlying computations by means of a unique, periodic synaptic matrix that could be self-organized in early development through a simple, symmetry-breaking operation.
Abstract: The hippocampal formation can encode relative spatial location, without reference to external cues, by the integration of linear and angular self-motion (path integration). Theoretical studies, in conjunction with recent empirical discoveries, suggest that the medial entorhinal cortex (MEC) might perform some of the essential underlying computations by means of a unique, periodic synaptic matrix that could be self-organized in early development through a simple, symmetry-breaking operation. The scale at which space is represented increases systematically along the dorsoventral axis in both the hippocampus and the MEC, apparently because of systematic variation in the gain of a movement-speed signal. Convergence of spatially periodic input at multiple scales, from so-called grid cells in the entorhinal cortex, might result in non-periodic spatial firing patterns (place fields) in the hippocampus.
1,747 citations
TL;DR: A new cell type is identified that signals the animal's head direction in its environment as well as the range of head-direction angles over which discharge was elevated and the location of the animal within the cylinder had minimal effect on directional cell firing.
Abstract: This paper is a study of the behavioral and spatial firing correlates of neurons in the rat postsubiculum. Recordings were made from postsubicular neurons as rats moved freely throughout a cylindrical chamber, where the major cue for orientation was a white card taped to the inside wall. An automatic video/computer system monitored cell discharge while simultaneously tracking the position of 2 colored light emitting diodes (LEDs) secured to the animal's head. The animal's location was calculated from the position of one of the LEDs and head direction in the horizontal plane calculated from the relative positions of the 2 LEDs. Approximately 26% of the cells were classified as head-direction cells because they discharged as a function of the animal's head direction in the horizontal plane, independent of the animal's behavior, location, or trunk position. For each head-direction cell, vectors drawn in the direction of maximal firing were parallel throughout the recording chamber and did not converge toward a single point. Plots of firing rate versus head direction showed that each firing-rate/head-direction function was adequately described by a triangular function. Each cell's maximum firing rate occurred at only one (the preferred) head direction; firing rates at head directions on either side of the preferred direction decreased linearly with angular deviation from the preferred direction. Results from 24 head-direction cells in 7 animals showed an equal distribution of preferred firing directions over a 360 degrees angle. The peak firing rate of head- direction cells varied from 5 to 115 spikes/sec (mean: 35). The range of head-direction angles over which discharge was elevated (directional firing range) was usually about 90 degrees, with little, if any, discharge at head directions outside this range. Quantitative analysis showed the location of the animal within the cylinder had minimal effect on directional cell firing. For each head-direction cell, the preferred direction, peak firing rate, and directional firing range remained stable for days. These results identify a new cell type that signals the animal's head direction in its environment.
1,664 citations