Biology subjects

Passlack, J.

Publications and source records attributed to Passlack, J..

3 recordsLinked to original sources

bioRxiv2026

Nucleus reuniens is organised as parallel circuits rather than a prefrontal-hippocampal relay

Interactions between the prefrontal cortex (PFC) and hippocampus (HPC) are crucial for flexible and memory guided behaviour. Because there are no direct projections from PFC to HPC, it is widely presumed that information is shared through a disynaptic projection via the nucleus reuniens (nRE), a ventral midline thalamic nucleus. Yet this model relies on the implicit assumption that has not been directly tested: that prefrontal afferents monosynaptically recruit hippocampal-projecting nRE neurons. Here we combine whole-brain anatomical mapping, projection-specific circuit tracing and electrophysiology to test this model. We find that nRE contains largely distinct populations of prefrontal- and hippocampal-projecting neurons, with minimal overlap between them. Unexpectedly, prefrontal afferent input to nRE provides little anatomical or functional input to hippocampal-projecting neurons, instead preferentially targeting neurons projecting back to PFC. These findings challenge the prevailing view that nRE acts as a simple relay between PFC and HPC and instead reveal parallel projection-defined circuits likely to make distinct contributions to hippocampal-prefrontal communication.

neuroscience↗

bioRxiv2025

Contextual inference through flexible integration of environmental features and behavioural outcomes

The ability to use the context we are in to flexibly adjust our decision-making is vital for navigating a complex world. To do this, the brain must i) use environmental features and behavioural outcomes to distinguish between different, often hidden contexts; and ii) learn how to use these inferred contexts to guide behaviour. However, how these two interacting processes can be performed simultaneously remains unclear. Within the brain it is thought that interaction between the prefrontal cortex (PFC) and hippocampus (HPC) supports contextual inference. We show that models of the HPC using environmental features readily support context-specific behaviour, but struggle to differentiate ambiguous contexts during learning. In contrast, models of the PFC using behavioural outcomes can stably differentiate contexts during periods of learning, but struggle to guide context-specific behaviour. Supporting feature-based with outcome-based strategies during learning overcomes the limitations of both approaches, allowing for the formation of distinct contextual representations that support contextual inference. Moreover, agents using this joint approach reproduce both behavioural- and cellular-level phenomena associated with the interaction between PFC and HPC. Together, these results provide insight into how the brain uses contextual information to guide flexible behaviour.

neuroscience↗

bioRxiv2019

Grid cells implement a location-dependent directional code

Grid and head direction codes represent cognitive spaces for navigation and memory. Pure grid cells generate grid codes that have been assumed to be independent of head direction, whereas conjunctive cells generate grid representations that are tuned to a single head direction. Here, we demonstrate that pure grid cells also encode head direction, but through distinct mechanisms. We show that individual firing fields of pure grid cells are tuned to multiple head directions, with the preferred sets of directions differing between fields. This local directionality is not predicted by previous continuous attractor or oscillatory interference models of grid firing but is accounted for by models in which pure grid cells integrate inputs from co-aligned conjunctive cells with firing rates that differ between their fields. Local directional signals from grid cells may contribute to downstream computations by decorrelating different points of view from the same location.

neuroscience↗