CORTICAL ENGRAM DENDRITES INFLUENCE LEARNT SENSORY ASSOCIATION BEHAVIOUR

Memory refers to the ability to store and retrieve information acquired through experience. While the consolidation mechanisms that support memory storage are well characterized, the processes that enable long-term memory retention remain unclear. Engram cells are a population of neurons which are fundamental for memory formation, storage and retrieval, and are known to encode memory traces through lasting synaptic changes. Since dendrites are the neuronal site where synaptic inputs are received and modified, dendrites may represent an important unit of memory formation and storage in engram cells. However, the properties of engram dendrites are largely unknown and were investigated here. Using in vivo two-photon calcium imaging and optogenetics, the dendrites of engram cells within the frontal cortex were investigated during learning of an auditory association task. Our findings reveal learning-dependent changes in engram dendrites, with increased calcium signalling during task-evoked responses in engram dendrites compared to non-engram dendrites. Optogenetic activation of engram cells specifically induces task-related behavioural responses in the absence of an external cue, suggesting cortical engram cells are directly involved in memory recall of learnt behaviour. These findings advance our understanding of the cellular mechanisms underlying long-term memory storage, highlighting dendrites as an important cellular unit of memory consolidation and storage.