Biology subjects

Naya, Y.

Publications and source records attributed to Naya, Y..

10 recordsLinked to original sources

bioRxiv2026

Coexisting but dissociable place and spatial view codes in the primate hippocampus

In rodents, hippocampal activity is classically described in terms of position-anchored place cells, whereas nonhuman primate work has emphasized spatial view cells, in which activity depends on the region of space being viewed. This contrast has fueled a longstanding debate over whether primate and rodent spatial codes are biologically distinct. We recorded single units in the hippocampus of macaques as they navigated linear tracks in two visually distinct contexts, intermittently making context-dependent object choices. Using a generalized linear model to dissociate position coding from spatial view coding, we identified three coexisting populations in the macaque hippocampus: Position cells, View cells, and Conjunctive cells encoding both variables. Position cells were prevalent and showed rodent-like properties--localized firing, directional tuning, and contextual remapping--even after accounting for visual sampling, whereas View cells stably encoded allocentric visual space. Population decoding confirmed this dissociation at the ensemble level. Robust position codes thus coexist with, yet remain dissociable from, view codes in the primate hippocampus, suggesting that the apparent scarcity of place-like responses in earlier primate work reflects methodological and task-related differences rather than a fundamental species-level divergence.

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bioRxiv2026

Forward processing of spatiotemporal maps across hippocampal subfields in common marmosets

Episodic memory requires distinguishing similar events occurring at the same location but at different times. While the hippocampus integrates "where" and "when," the specific roles of the primate dentate gyrus (DG) and CA3 remain elusive. We recorded single-unit activity from freely moving marmosets navigating a spatial maze in a visually impoverished environment. Both hippocampal subfields robustly encoded self-position via neurons selective for stationary epochs at platforms and movement along trajectories, whereas gaze-related coding was minimal. While DG signaled stationary and dynamic self-positions independently, CA3 integrated these elements into conjunctive representations. Critically, only CA3 neurons exhibited strong temporal-order modulation. These findings reveal a feedforward disambiguation process in which CA3 transforms discrete spatial inputs from DG into the integrated spatiotemporal maps essential for episodic memory.

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bioRxiv2026

The orbitofrontal cortex constructs allocentric schemas by integrating dynamic mobile agents with static environmental anchors

Scene construction involves the automatic synthesis of fragmented visual inputs into coherent mental models. While previous work has focused on static landscapes, real-world scenes require integrating dynamic agents with stable environmental anchors. We investigated the neural hierarchy underlying this transformation using an automatic space-encoding task in a 3D virtual-reality environment and fMRI representational similarity analysis. Results revealed functional segregation across visual cortex: the superior lateral occipital cortex encoded the first-person perspective of mobile character layouts, whereas the lingual gyrus and occipital fusiform cortex represented environments specified by visible landmarks. The orbitofrontal cortex integrated these streams into an allocentric spatial schema, capturing relational geometry beyond the current visual field. Following encoding, these representations were expressed in the anterior hippocampus for self-localization. Together, the findings demonstrate an automatic hierarchical transformation in which the OFC serves as a central scaffold for constructing allocentric spatial frameworks underlying stable scene representation.

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bioRxiv2024

Formation of brain-wide neural geometry during visual item recognition in monkeys

Neural dynamics assumes to reflect computations that relay and transform information in the brain. Previous studies have identified the neural population dynamics in many individual brain regions as a trajectory geometry, preserving a manifest of computational motifs. However, whether these populations share particular geometric patterns across brain-wide neural populations remains unclear. Here, by mapping neural dynamics widely across temporal/frontal/limbic regions in the cortical and subcortical structures of monkeys, we show that 10 neural populations, including 2,500 neurons, propagate visual item information in a stochastic manner. We found that visual inputs predominantly evoked rotational dynamics in the higher-order visual area, TE and its downstream striatum tail, while curvy/straight dynamics appeared frequently downstream in the orbitofrontal/hippocampal network. These geometric changes were not deterministic but rather stochastic according to their respective emergence rates. Our meta-analysis results indicated that visual information propagates as a heterogeneous mixture of stochastic neural population signals in the brain.

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bioRxiv2022

Sequential involvements of macaque perirhinal cortex and hippocampus in semantic-like memory including spatial component

The standard consolidation theory suggests the critical involvement of the hippocampus (HPC) in acquiring new knowledge, while the perirhinal cortex (PRC) is involved in its long-term storage (i.e., semantic memory). Converging studies have shown exclusive involvement of the PRC in item processing, while the HPC relates the item with a spatial context. These two lines of literature raise the following question; which brain region is involved in semantic recall that includes the spatial components? To solve this question, we applied an item-location associative (ILA) paradigm in a single-unit study using non-human primates. We trained two macaques to associate four visual item pairs with four locations on a background map before the recording sessions. In each trial, one visual item and the map image at a tilt (-90 to 90 degrees) were sequentially presented as the item-cue and the context-cue, respectively. The macaques chose the item-cue location relative to the context-cue by positioning their gaze. Neurons in both PRC and HPC but not area TE exhibited item-cue responses which signaled retrieval of item-location associative memory. This retrieval signal first appeared in the PRC before appearing in the HPC. We examined whether neural representations of the retrieved locations were related to the external space where the macaques viewed. A positive representation similarity was found in the HPC but not PRC, suggesting a contribution of the HPC to relate the retrieved location with a first-person perspective of the subjects. These results suggest their distinct but complementary contributions to semantic recall including spatial components.

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bioRxiv2022

Comparison of neural population dynamics in the regression subspace between continuous and categorical task parameters

Neural population dynamics, presumably fundamental computational units in the brain, provide a key framework for understanding information processing in the sensory, cognitive, and motor functions. However, neural population dynamics is not explicitly related to the conventional analytic framework for single-neuron activity, i.e., representational models that analyze neuronal modulations associated with cognitive and motor parameters. In this study, we applied a recently developed state-space analysis to incorporate the representational models into the dynamic model in combination with these parameters. We compared neural population dynamics between continuous and categorical task parameters during two visual recognition tasks, using the datasets originally designed for a single-neuron approach. We successfully extracted neural population dynamics in the regression subspace, which represent modulation dynamics for both continuous and categorical task parameters with reasonable temporal characteristics. Furthermore, we combined the classical optimal-stimulus analysis paradigm for the single-neuron approach (i.e., stimulus identified as maximum neural responses) into the dynamic model, and found that the most prominent modulation dynamics at the lower dimension were derived from these optimal responses. Thus, our approach provides a unified framework for incorporating knowledge acquired with the single-neuron approach into the dynamic model as a standard procedure for describing neural modulation dynamics in the brain.

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bioRxiv2020

Distinct brain networks coupled with the parietal cortex represent target location inside and outside the visual field

Our mental representation of egocentric space is influenced by the disproportionate sensory perception of the body. Previous studies have focused on the neural architecture for egocentric representations within the visual field. However, the space representation underlying the body is still unclear. To address this problem, we applied both fMRI and MEG to a spatial-memory paradigm by using a virtual environment in which human participants remembered a target location left, right, or back relative to their own body. Both experiments showed larger involvement of the frontoparietal network in representing a retrieved target on the left/right side than on the back. Conversely, the medial temporal lobe (MTL)-parietal network was more involved in retrieving a target behind the participants. The MEG data showed preferential connectivity in the alpha-band frequency in both networks. These findings suggest that the parietal cortex may represent the entire space around the self-body by coordinating two distinct brain networks.

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bioRxiv2020

Hippocampal cells integrate past memory and present perception for the future

The ability to use stored information in a highly flexible manner is a defining feature of the declarative memory system. However, the neuronal mechanisms underlying this flexibility are poorly understood. To address this question, we recorded single-unit activity from the hippocampus of two non-human primates performing a newly devised task requiring the monkeys to retrieve long-term item-location association memory and then use it flexibly in different circumstances. We found that hippocampal neurons signaled both mnemonic information representing the retrieved location and perceptual information representing the external circumstance. The two signals were combined at a single-neuron level to construct goal-directed information by three sequentially occurring neuronal operations (e.g., convergence, transference, targeting) in the hippocampus. Thus, flexible use of knowledge may be supported by the hippocampal constructive process linking memory and perception, which may fit the mnemonic information into the current situation to present manageable information for a subsequent action.

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bioRxiv2020

Automatic encoding of a view-centered background image in the macaque temporal lobe

Perceptual processing along the ventral visual pathway to the hippocampus is hypothesized to be substantiated by signal transformation from retinotopic space to relational space, which represents interrelations among constituent visual elements. However, our visual perception necessarily reflects the first persons perspective based on the retinotopic space. To investigate this two-facedness of visual perception, we compared neural activities in the temporal lobe (anterior inferotemporal cortex, perirhinal and parahippocampal cortices, and hippocampus) between when monkeys gazed on an object and when they fixated on the screen center with an object in their peripheral vision. We found that in addition to the spatially invariant object signal, the temporal lobe areas automatically represent a large-scale background image, which specify the subjects viewing location. These results suggest that a combination of two distinct visual signals on relational space and retinotopic space may provide the first persons perspective serving for perception and presumably subsequent episodic memory.

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bioRxiv2019

Object-Based Cognitive Map in the Human Hippocampus and Medial Prefrontal Cortex

A cognitive map, representing an environment around oneself, is necessary for spatial navigation. However, compared with its constituent elements such as individual landmarks, neural substrates of coherent spatial information remain largely unknown. The present study investigated how the brain codes map-like representations in a virtual environment specified by the relative positions of three objects. Representational similarity analysis revealed an object-based spatial representation in the hippocampus (HPC) when participants located themselves within the environment, while the medial prefrontal cortex (mPFC) represented it when they recollected a target objects location relative to their self-body. During recollection, task-dependent functional connectivity increased between the two areas implying exchange of self- and target-location signals between the HPC and mPFC. Together, the coherent cognitive map, which could be formed by objects, may be recruited in the HPC and mPFC for complementary functions during navigation, which may generalize to other aspects of cognition, such as navigating social interactions.

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