Flexible cue anchoring strategies enable stable head direction coding in both sighted and blind animals

Stereo olfaction underlies stable coding of head direction in blind mice

Stereo olfaction, the difference in odor concentration between the two nostrils, has been shown to affect a variety of animal behaviors, including olfactory search. However, it is unknown whether stereo olfaction can enable the formation of allocentric spatial representations. Here, recording from head direction (HD) cells in the anterior dorsal nucleus of the thalamus in blind mice-a model system for studying olfaction-dependent allocentric spatial representations-we find that inhibiting stereo olfaction, by blocking olfactory processing in one nostril or merging the airflow going to both nostrils, drastically impairs head direction coding. To assess the behavioral impact of impaired HD cell tuning caused by loss of stereo olfaction, we developed a closed-loop head direction preference assay, in which a mouse received medial forebrain bundle reward stimulation upon orientating its head in a specific direction. We find that inhibiting stereo olfaction significantly impairs performance in the HD preference assay. These results reveal that stereo olfaction is required for mice to use smell to form a stable allocentric spatial representation of head direction.

Shortcutting from self-motion signals reveals a cognitive map in mice

Animals navigate by learning the spatial layout of their environment. We investigated spatial learning of mice in an open maze where food was hidden in one of a hundred holes. Mice leaving from a stable entrance learned to efficiently navigate to the food without the need for landmarks. We developed a quantitative framework to reveal how the mice estimate the food location based on analyses of trajectories and active hole checks. After learning, the computed 'target estimation vector' (TEV) closely approximated the mice's route and its hole check distribution. The TEV required learning both the direction and distance of the start to food vector, and our data suggests that different learning dynamics underlie these estimates. We propose that the TEV can be precisely connected to the properties of hippocampal place cells. Finally, we provide the first demonstration that, after learning the location of two food sites, the mice took a shortcut between the sites, demonstrating that they had generated a cognitive map.

The dorsal thalamic lateral geniculate nucleus is required for visual control of head direction cell firing direction in rats

Head direction (HD) neurons, signalling facing direction, generate a signal that is primarily anchored to the outside world by visual inputs. We investigated the route for visual landmark information into the HD system in rats. There are two candidates: an evolutionarily older, larger subcortical retino-tectal pathway and a more recently evolved, smaller cortical retino-geniculo-striate pathway. We disrupted the cortical pathway by lesioning the dorsal lateral geniculate thalamic nuclei bilaterally, and recorded HD cells in the postsubicular cortex as rats foraged in a visual-cue-controlled enclosure. In lesioned rats we found the expected number of postsubicular HD cells. Although directional tuning curves were broader across a trial, this was attributable to the increased instability of otherwise normal-width tuning curves. Tuning curves were also poorly responsive to polarizing visual landmarks and did not distinguish cues based on their visual pattern. Thus, the retino-geniculo-striate pathway is not crucial for the generation of an underlying, tightly tuned directional signal but does provide the main route for vision-based anchoring of the signal to the outside world, even when visual cues are high in contrast and low in detail. KEY POINTS: Head direction (HD) cells indicate the facing direction of the head, using visual landmarks to distinguish directions. In rats, we investigated whether this visual information is routed through the thalamus to the visual cortex or arrives via the superior colliculus, which is a phylogenetically older and (in rodents) larger pathway. We lesioned the thalamic dorsal lateral geniculate nucleus (dLGN) in rats and recorded the responsiveness of cortical HD cells to visual cues. We found that cortical HD cells had normal tuning curves, but these were slightly more unstable during a trial. Most notably, HD cells in dLGN-lesioned animals showed little ability to distinguish highly distinct cues and none to distinguish more similar cues. These results suggest that directional processing of visual landmarks in mammals requires the geniculo-cortical pathway, which raises questions about when and how visual directional landmark processing appeared during evolution.

Experience of Euclidean geometry sculpts the development and dynamics of rodent hippocampal sequential cell assemblies

Euclidean space is the fabric of the world we live in. Whether and how geometric experience shapes our spatial-temporal representations of the world remained unknown. We deprived male rats of experience with crucial features of Euclidean geometry by rearing them inside spheres, and compared activity of large hippocampal neuronal ensembles during navigation and sleep with that of cuboid cage-reared controls. Sphere-rearing from birth permitted emergence of accurate neuronal ensemble spatial codes and preconfigured and plastic time-compressed neuronal sequences. However, sphere-rearing led to diminished individual place cell tuning, more similar neuronal mapping of different track ends/corners, and impaired pattern separation and plasticity of multiple linear tracks, coupled with reduced preconfigured sleep network repertoires. Subsequent experience with multiple linear environments over four days largely reversed these effects. Thus, early-life experience with Euclidean geometry enriches the hippocampal repertoire of preconfigured neuronal patterns selected toward unique representation and discrimination of multiple linear environments.

Altered grid-like coding in early blind people

Cognitive maps in the hippocampal-entorhinal system are central for the representation of both spatial and non-spatial relationships. Although this system, especially in humans, heavily relies on vision, the role of visual experience in shaping the development of cognitive maps remains largely unknown. Here, we test sighted and early blind individuals in both imagined navigation in fMRI and real-world navigation. During imagined navigation, the Human Navigation Network, constituted by frontal, medial temporal, and parietal cortices, is reliably activated in both groups, showing resilience to visual deprivation. However, neural geometry analyses highlight crucial differences between groups. A 60° rotational symmetry, characteristic of a hexagonal grid-like coding, emerges in the entorhinal cortex of sighted but not blind people, who instead show a 90° (4-fold) symmetry, indicative of a square grid. Moreover, higher parietal cortex activity during navigation in blind people correlates with the magnitude of 4-fold symmetry. In sum, early blindness can alter the geometry of entorhinal cognitive maps, possibly as a consequence of higher reliance on parietal egocentric coding during navigation.

Sensory and behavioral modulation of thalamic head-direction cells

Head-direction (HD) neurons are thought to exclusively encode directional heading. In awake mice, we found that sensory stimuli evoked robust short-latency responses in thalamic HD cells, but not in non-HD neurons. The activity of HD cells, but not that of non-HD neurons, was tightly correlated to brain-state fluctuations and dynamically modulated during social interactions. These data point to a new role for the thalamic compass in relaying sensory and behavioral-state information.

Geometric experience sculpts the development and dynamics of hippocampal sequential cell assemblies

Euclidean space is the fabric of the world we live in. Whether and how geometric experience shapes our spatial-temporal representations of the world remained unknown. We deprived rats of experience with crucial features of Euclidean geometry by rearing them inside translucent spheres, and compared activity of large hippocampal neuronal ensembles during navigation and sleep with that of cuboid cage-reared controls. Sphere-rearing from birth permitted emergence of accurate neuronal ensemble spatial codes and preconfigured and plastic time-compressed neuronal sequences. However, sphere-rearing led to diminished individual place cell tuning, similar neuronal mapping of different track ends/corners, and impaired neuronal pattern separation and plasticity of multiple linear track experiences, partly driven by reduced preconfigured network repertoires. Subsequent experience with multiple linear environments over four days largely reversed these effects, substantiating the role of geometric experience on hippocampal neural development. Thus, early-life experience with Euclidean geometry enriches the hippocampal repertoire of preconfigured neuronal patterns selected toward unique representation and discrimination of multiple linear environments.

Angular Head Velocity Cells within Brainstem Nuclei Projecting to the Head Direction Circuit

The sense of orientation of an animal is derived from the head direction (HD) system found in several limbic structures and depends on an intact vestibular labyrinth. However, how the vestibular system influences the generation and updating of the HD signal remains poorly understood. Anatomical and lesion studies point toward three key brainstem nuclei as key components for generating the HD signal-nucleus prepositus hypoglossi, supragenual nucleus, and dorsal paragigantocellularis reticular nuclei. Collectively, these nuclei are situated between the vestibular nuclei and the dorsal tegmental and lateral mammillary nuclei, which are thought to serve as the origin of the HD signal. To determine the types of information these brain areas convey to the HD network, we recorded neurons from these regions while female rats actively foraged in a cylindrical enclosure or were restrained and rotated passively. During foraging, a large subset of cells in all three nuclei exhibited activity that correlated with the angular head velocity (AHV) of the rat. Two fundamental types of AHV cells were observed; (1) symmetrical AHV cells increased or decreased their firing with increases in AHV regardless of the direction of rotation, and (2) asymmetrical AHV cells responded differentially to clockwise and counterclockwise head rotations. When rats were passively rotated, some AHV cells remained sensitive to AHV, whereas firing was attenuated in other cells. In addition, a large number of AHV cells were modulated by linear head velocity. These results indicate the types of information conveyed from the vestibular nuclei that are responsible for generating the HD signal.SIGNIFICANCE STATEMENT Extracellular recording of brainstem nuclei (nucleus prepositus hypoglossi, supragenual nucleus, and dorsal paragigantocellularis reticular nucleus) that project to the head direction circuit identified different types of AHV cells while rats freely foraged in a cylindrical environment. The firing of many cells was also modulated by linear velocity. When rats were restrained and passively rotated, some cells remained sensitive to AHV, whereas others had attenuated firing. These brainstem nuclei provide critical information about the rotational movement of the head of the rat in the azimuthal plane.

The neurobiology of the Monarch butterfly compass

Monarch butterflies (Danaus plexippus) have become a superb model system to unravel how the tiny insect brain controls an impressive navigation behavior, such as long-distance migration. Moreover, the ability to compare the neural substrate between migratory and nonmigratory Monarch butterflies provides us with an attractive model to specifically study how the insect brain is adapted for migration. We here review our current progress on the neural substrate of spatial orientation in Monarch butterflies and how their spectacular annual migration might be controlled by their brain. We also discuss open research questions, the answers to which will provide important missing pieces to obtain a full picture of insect migration - from the perception of orientation cues to the neural control of migration.

How Do You Build a Cognitive Map? The Development of Circuits and Computations for the Representation of Space in the Brain

In mammals, the activity of neurons in the entorhinal-hippocampal network is modulated by the animal's position and its movement through space. At multiple stages of this distributed circuit, distinct populations of neurons can represent a rich repertoire of navigation-related variables like the animal's location, the speed and direction of its movements, or the presence of borders and objects. Working together, spatially tuned neurons give rise to an internal representation of space, a cognitive map that supports an animal's ability to navigate the world and to encode and consolidate memories from experience. The mechanisms by which, during development, the brain acquires the ability to create an internal representation of space are just beginning to be elucidated. In this review, we examine recent work that has begun to investigate the ontogeny of circuitry, firing patterns, and computations underpinning the representation of space in the mammalian brain.

Coregistration of heading to visual cues in retrosplenial cortex

Spatial cognition depends on an accurate representation of orientation within an environment. Head direction cells in distributed brain regions receive a range of sensory inputs, but visual input is particularly important for aligning their responses to environmental landmarks. To investigate how population-level heading responses are aligned to visual input, we recorded from retrosplenial cortex (RSC) of head-fixed mice in a moving environment using two-photon calcium imaging. We show that RSC neurons are tuned to the animal's relative orientation in the environment, even in the absence of head movement. Next, we found that RSC receives functionally distinct projections from visual and thalamic areas and contains several functional classes of neurons. While some functional classes mirror RSC inputs, a newly discovered class coregisters visual and thalamic signals. Finally, decoding analyses reveal unique contributions to heading from each class. Our results suggest an RSC circuit for anchoring heading representations to environmental visual landmarks.