SLEEP PROMOTES THE FORMATION OF CONJUNCTIVE REPRESENTATION OF THE ITEM-CONTEXT MEMORY IN MICE

Sleep is known to support memory formation. Previous studies suggest that active systems consolidation during sleep involves the binding of concurrent representations of events and a learning context. However, whether and how sleep supports the formation of conjunctive representations of separate learning elements is not well understood.
Here we used the Context Preexposure Facilitation Effect (CPFE) paradigm in mice to specifically dissociate the formation of a contextual representation from an aversive stimulus, providing a suitable framework to investigate how sleep contributes separately to the formation of contextual representations and the context-shock association. C57BL/6J mice were first pre-exposed to a chamber (Context A) to establish a stable contextual representation. On the following day, an immediate foot shock (2 seconds) was delivered to induce context-shock associative learning, after which animals either slept or remained awake for 3 hours. Fear memory was assessed 24 hours later by introducing the mice into both pre-exposed Context A and a novel chamber (Context B). Mice that slept after context-shock association learning elicited significant freezing behaviour in Context A, but not in Context B, suggesting discriminative contextual fear response. However, sleep-deprived mice significantly reduced freezing behaviour in Context A compared to the sleep group and showed no freezing in Context B.
Our preliminary results indicate that sleep is required for the formation of conjunctive memory representations, binding together a single learning event and contextual information into a unitary memory representation.