The Cognitive Neuroscience of Memory Representations

We discuss the concept of a memory representation from the perspective of the cognitive neuroscience of long-term memory, focusing on episodic memory and differentiating active versus latent, and cognitive versus neural representations. We adopt a causal perspective, according to which an active cognitive representation must have a causal connection to a past event to count as a memory. We note that retrieved episodic information may nonetheless only partially determine the content of an active memory representation, which can comprise a combination of the retrieved information with semantic, schematic and situational information. We further note that, especially in the case of memories for temporally remote events, re-encoding operations likely lead to a causal chain that extends from the original experience of the event to its currently accessible memory trace. We discuss how the reinstatement framework provides a mechanistic basis for the causal linkage between an experience, the memory trace encoding it, and the retrieval of an episodic memory of the experience, highlighting the crucial role of hippocampal engrams in encoding patterns of neocortical activity that, when activated, constitute the neural representation of an episodic memory. Finally, we discuss some of the ways in which a memory can become modified and hence distanced from the episode that precipitated it.