Investigating episodic and semantic memory: neural correlates and novel learning techniques

Episodic and semantic memory are often thought of as separate but closely linked memory systems; however, the precise relationship between these systems is yet to be fully characterised. Here, I investigate the neural correlates of episodic and semantic memory in an attempt to understand the contributions of different brain regions to each memory system. I also assess the potential benefits of a novel learning technique for use by individuals with episodic memory impairment. Chapter 2 uses fMRI and representational similarity analyses to explore the contributions of posterior midline structures to both episodic and semantic memory. I present evidence for the role of the retrosplenial cortex in representing episodic, but not semantic, information, whereas the precuneus and posterior cingulate cortex appear to play a role in representing the semantic content of memories. Chapter 3 also uses representational similarity analyses with fMRI data but focuses on semantic memory, exploring how different aspects of semantic concepts are represented in the anterior temporal lobes. Chapter 4 uses computational modelling and behavioural data to compare two theories of the mechanisms underlying a novel learning technique, cross-situational learning, the results of which suggest that cross-situational learning is supported by a statistical learning mechanism. Finally, Chapter 5 assesses the benefit of using cross-situational learning over standard explicit encoding methods in individuals diagnosed with mild cognitive impairment or Alzheimer’s disease when learning novel object-label pairs. The results suggest that while cross-situational learning provides no benefit to the amount of information learned, the newly learned information is less likely to be forgotten. Together, this research shows that regions within the posterior midline and temporal lobes have differential contributions to episodic and semantic memory, therefore providing evidence for the dissociation of these memory types. This dissociation can then be leveraged to aid individuals with episodic memory impairment by using learning techniques that encourage alternative routes of encoding novel information.