Search

Recordings from rat grid cells, cells that are active at periodically spaced locations in the environment, show that they are organized into discrete modules that maintain distinct scale and orientation, and may respond independently to environmental changes.

Neural population activity in the medial entorhinal cortex of mice can be organized into ultraslow oscillatory sequences, with periods extending up to the minute range.

Neuroscientists are increasingly using virtual reality to facilitate studies of animal behaviour, but whether behaviour in the virtual world mimics that in real life is a matter for debate. Here, scientists discuss the strengths and limitations of the approach.

How neural responses to boundaries develop in the subiculum remains unknown. Here authors show that the receptive fields of Boundary Vector Cells (neurons signalling vector displacement to boundaries) are altered by environment geometry, with directional tunings aligning with square arena walls, including during development.

Grid cells are cells of the brain’s internal map of space that fire when an animal is in a location corresponding to the vertices of a hexagonal grid pattern tiling the entire environment; how the pattern is mapped onto the external environment has remained a mystery, however, new studies in rat reveal that the axes of the grid are determined by the boundaries of the external environment and provide insight into the rotation of the grid axis in relation to these boundaries.

On the basis of neural firing rates a specific class of neuron is identified in the medial entorhinal cortex that linearly encodes information on running speed in a context-independent manner and that is distinct from other functionally specific entorhinal neurons.

Nervous systems recreate properties of the environment in activity patterns referred to as neural representations. In this Review, Moser and colleagues examine how grid cells in the medial entorhinal cortex contribute to the neural representation of external space.

A study in rats proposes a mechanism for how the brain maps the surrounding environment, including places it has never seen, by alternating left and right forward sweeps in successive theta cycles.

Simultaneous recordings from hundreds of grid cells in rats, combined with topological data analysis, show that network activity in grid cells resides on a toroidal manifold that is invariant across environments and brain states.

Simultaneous recordings from hippocampus and entorhinal cortex in rats show that as the animals learn odour guidance cues during their exploration of two-dimensional space in the laboratory, ensembles of coherently firing neurons emerge in both locations, with cortical–hippocampal oscillatory coupling occurring in a specific range of the beta-gamma frequency band.

The resting brain recapitulates activity patterns that occurred during a recent experience, possibly to aid long-term memory formation. Surprisingly, corresponding brain activity also occurs before an event happens. See Letter p.397

Temporal information that is useful for episodic memory is encoded across a wide range of timescales in the lateral entorhinal cortex, arising inherently from its representation of ongoing experience.

Recording from cell ensembles in the medial entorhinal cortex, Gardner et al. show that the correlation structure of the grid cell system is preserved between awake and sleep states. This rigidity is a signature of continuous attractor networks.

The parahippocampal region of dorsal presubinculum has neurons that preferentially fire based on the direction of the rat's head. The medial entorhinal cortex has neurons that are preferentially active according to grid-like regularity in space. Here, the authors find that pre- and parasubiculum also have these grid cells, which are intermingled with head-direction cells.

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.

In the hippocampus, coordinates in space are thought to be expressed by the collective firing locations of place cells while the diversity of experience at these locations is encoded by orthogonal variations in firing rates. Here the authors show that these rate variations in CA3 place cells depend on inputs from the lateral entorhinal cortex.

The authors investigate grid cell dynamics after removal of a border between two environments. Near the transition between environments, grid fields changed location, resulting in local spatial periodicity and continuity between the original maps.

The authors recorded neural activity in grid cells while rats ran through a hairpin maze. Their results demonstrate that spatial environments are represented in the entorhinal cortex and hippocampus as a mosaic of discrete submaps corresponding to the geometric structure of the space.

Grid cells have been proposed to reflect competitive interactions in inhibitory neural networks. Experimental results obtained using optogenetics to identify spikes emitted specifically by parvalbumin interneurons now constrain the mechanisms by which such networks could give rise to grid cells.

In the brain, both rate and temporal codes are critical for information storage. Theta phase precession is a change in action potential timing in the hippocampus where place cells fire at progressively earlier phases of the theta rhythm as the animal moves across the firing field of the neuron. This paper explores the circuitry of theta phase precession and shows that phase precession is expressed independently of the hippocampus in spatially modulated grid cells in parts of the entorhinal cortex.

Gamma oscillations in the brain are thought to 'bind' spatially distributed cells, a function that is probably important in perception, attentional selection and memory. However, it is unclear why the frequency of gamma oscillations varies substantially across space and time. Here, the study of the frequency of gamma oscillations in the CA1 area of the hippocampus suggests that variations in gamma frequency may be important for routeing information in the brain.

Cells in the mouse medial entorhinal cortex that fire when mice are at a specific distance and direction from a stationary object suggest that vector coding is important for rodent navigation.

Few brain circuits have generated more research than the mammalian hippocampus, a region of discrete subfields that connect serially to form a 'trisynaptic loop'. A new paper implies that the loop may be made up of parallel subpathways.

Trajectory-dependent firing of neurons within the nucleus reuniens of the thalamus–hippocampus circuit predicted subsequent running direction, and disruption of this circuit reduced predictive firing in the hippocampus, suggesting that the thalamus is a key node in the integration of signals during goal-oriented navigation.

Mammals keep track of relative position and orientation by integrating self-motion cues. McNaughton and colleagues discuss the neurobiological evidence for a synaptic matrix capable of performing this task, and propose a model for how this neuronal network might arise developmentally.

In this review, György Buzsáki and Edvard Moser discuss the most recent evidence suggesting that the navigation and memory functions of the hippocampus and entorhinal cortex are supported by the same neuronal algorithms. They propose that the mechanisms fueling the memory and mental travel engines in the hippocampal-entorhinal system evolved from the mechanisms supporting navigation in the physical world.

Using paired recordings from rat entorhinal stellate cells and computational modeling, this study shows that stellate cells in the medial entorhinal cortex (MEC) are almost exclusively connected to each other via inhibitory interneurons in an all-or-none style and that stable grid firing can arise from this recurrent inhibitory circuitry within the MEC.

Moser, Moser and McNaughton provide a historical overview describing how ideas about integration of self-motion cues have shaped our understanding of spatial representation in hippocampal–entorhinal systems, from the discovery of place cells in the 1970s to contemporary studies of spatial coding in intermingled and interacting cell types within complex circuits.

It is commonly thought that the dorsal hippocampus is implicated in memory and spatial navigation and the ventral hippocampus in anxiety-related behaviours. On the basis of gene expression, anatomical and electrophysiology studies, Strange and colleagues propose a new model of hippocampal functional anatomy, in which functional long-axis gradients are superimposed on discrete functional domains.

The firing of most hippocampal neurons is modulated by the theta rhythm, but it's not clear how and where the rhythm is generated. A study now shows that the required machinery for theta generation lies in local circuits of the hippocampus.

The brain's hippocampal region contains many classes of interneurons, which, it transpires, show different patterns of activity. They might contribute to memory by shaping the dynamics of neuronal networks.

How does the brain store sequences of experience? Clues come from brain recordings of rats running along a track. The animals' memories seem to be consolidated in an unexpected way as they rest between runs.

One major form of timing is the estimation of duration. In this Review, Tsao et al. describe the neural bases for estimating ongoing durations and those for estimating durations between past events within memory.

In order to understand more about which object features are the most influential when driving vectorial responses, Andersson et al. use an algorithm to reliably examine object-vector (OV) cells in mice. Their findings suggest that OV cells use visual features as anchoring points, allowing vector-guided navigation to proceed with reference to a wide range of visual landmarks.

Local field potential recordings of the hippocampus reveal three types of neural activity rhythms: theta, sharp wave–ripples and gamma. In this Review, Colgin discusses recent findings from rodent studies that provide insight into the origin of these rhythms and their roles in memory and other behaviours.