THE ORGANISATION AND EXPRESSION OF OBJECT MEMORY IN OPEN AND STRUCTURED ENVIRONMENTS IS HIGHLY CONTEXT-DEPENDENT​

In complex environments, organisms must delineate boundaries between global contexts and parcellations within a given context. Physical borders offer a means to segment spatial representations thus allowing spatial ‘indexing’ of context relevant information. Accordingly, spatial segmentation has been proposed to support episodic memory by partitioning ongoing experience into discrete events (doi:10.1037/0033-2909.133.2.273), therefore limiting interference between similar experiences that share high feature overlap (doi:10.1016/j.tics.2013.01.001). Despite confirmation in global spatial environments, it remains unclear whether sub-boundaries, within a context, support event memory in a similar manner. To explore this, we developed an object recognition paradigm, for rats, based on an open field arena where animals must discriminate between known and novel objects characterised by low feature, or high feature, overlap. We found that rats expressed significant novelty preference towards novel objects with low feature overlap, but not towards those with high feature overlap. Introducing sub-borders to the arena was sufficient to instate novelty preference in animals discriminating between high feature overlap objects. Using multiplexed fluorescent in situ hybridization (FISH) targeting experience-dependent nuclear expression of the immediate early genes (IEG), Homer1a, Arc and cFos, we scrutinised neuronal populations in the perirhinal cortex, given its known role in object discrimination (doi: 10.1016/j.neubiorev.2022.104855) and detected subfield differentiations of IEG expression in this structure, relative to the behavioural condition tested. Taken together, our findings suggest that the disambiguation of highly similar objects involves spatial indexing and is supported in a context-dependent manner by subfields of the perirhinal cortex.