El Mahmoudi, N. | Search bioRxiv

bioRxiv2025

Dynamics of thalamic directional coding under vestibular imbalance

Head direction cells (HDCs) encode the animals orientation in space and form a core component of the brains navigation system. While their dependence on vestibular input is well established, how directional circuits respond to unilateral vestibular loss (UVL) -- the most frequent and ecologically relevant form of vestibular imbalance -- remains largely unknown. UVL offers a powerful model to investigate how spatial circuits adapt to asymmetric sensory disruption and partial deafferentation. To explore this, we examined the impact of UVL on anterior thalamic nuclei (ATN) activity and spatially tuned neurons in freely moving rats following unilateral vestibular neurectomy (UVN). UVN induced long-lasting alterations in ATN firing dynamics, including reduced theta modulation, diminished burst firing, and selective disruption across functionally defined neuronal classes: head-direction and speed-modulated cells were strongly affected, while angular head velocity and position cells remained largely preserved. Despite initial degradation, HDCs persisted and progressively regained directional tuning. Crucially, spike waveform analysis revealed two distinct HDC subtypes with markedly different vulnerabilities: one subtype showed reduced prevalence and degraded tuning, whereas the other remained resilient and supported the recovery of directional coding. These findings uncover a previously unrecognized heterogeneity within the head direction system and show that compensation following UVL is partial, cell type-specific, and functionally selective. Together, they offer new insight into sensory plasticity within thalamic navigation circuits and provide a framework to understand spatial deficits associated with vestibular imbalance.

neuroscience↗

bioRxiv2025

From Exploration to Structured Navigation: Learning Dynamics of Freely Moving Marmosets during Foraging

How do structured, memory-guided behaviors emerge in freely moving primates? We addressed this question by training common marmosets to perform a foraging task in a semi-naturalistic environment, where they retrieved food from eight dispensers over multiple sessions. Animals received no instruction or shaping and were free to visit dispensers in any order. We found that animals engaged with the task in most trials and, within engaged trials, transitioned from exploratory to efficient foraging behavior. Learning was marked by performance gains and the emergence of reproducible movement patterns between specific dispensers. Using trajectory analyses and probabilistic modeling, we found that animals formed stable route segments linking specific dispensers, reflecting the emergence of local navigation motifs. These segments became increasingly regular and predictable with experience. Yet rather than being rigidly replayed, they were flexibly recombined into variable global sequences. This indicates that animals adopted a hybrid navigation strategy, in which reusable route segments are embedded within a topological structure. These findings demonstrate how efficient, adaptive navigation can emerge through self-guided experience in complex environments. Our approach provides a naturalistic and longitudinal framework for studying the formation of structured spatial strategies in non-human primates, bridging ecological behavior with theoretical models of learning and memory.

animal behavior and cognition↗