The Pivotal Role of Semantic Memory in Remembering the Past and Imagining the Future

Abstract

Episodic memory refers to a complex and multifaceted process which enables the retrieval of richly detailed evocative memories from the past. In contrast, semantic memory is conceptualized as the retrieval of general conceptual knowledge divested of a specific spatiotemporal context. The neural substrates of the episodic and semantic memory systems have been dissociated in healthy individuals during functional imaging studies, and in clinical cohorts, leading to the prevailing view that episodic and semantic memory represent functionally distinct systems subtended by discrete neurobiological substrates. Importantly, however, converging evidence focusing on widespread neural networks now points to significant overlap between those regions essential for retrieval of autobiographical memories, episodic learning, and semantic processing. Here we review recent advances in episodic memory research focusing on neurodegenerative populations which has proved revelatory for our understanding of the complex interplay between episodic and semantic memory. Whereas episodic memory research has traditionally focused on retrieval of autobiographical events from the past, we also include evidence from the recent paradigm shift in which episodic memory is viewed as an adaptive and constructive process which facilitates the imagining of possible events in the future. We examine the available evidence which converges to highlight the pivotal role of semantic memory in providing schemas and meaning whether one is engaged in autobiographical retrieval for the past, or indeed, is endeavoring to construct a plausible scenario of an event in the future. It therefore seems plausible to contend that semantic processing may underlie most, if not all, forms of episodic memory, irrespective of temporal condition.

A taxonomy of prospection: Introducing an organizational framework for future-oriented cognition

“…In relation to future thinking, cognitive neuroscientists and neuropsychologists have generated considerable evidence showing that the capacity to remember past events and imagine future events is closely related, spurring the suggestion that event details can be flexibly extracted and recombined from memory in the service of simulating new events that may take place in the future (20). Here, we extend this proposed relation between memory and future thinking to highlight, as others have done as well (4,11,12,21,22), that general knowledge about the world (semantic knowledge) may also lay the groundwork for allowing us to reason about what the world may be like in the future. However, much work is needed to show these proposed relations between different types of knowledge and future thinking.…”

“…Moreover, it will be important to assess the extent to which these types of knowledge may interact with one another in the service of future-oriented cognition. For example, according to the semantic scaffolding hypothesis (21), semantic knowledge provides a framework or scaffolding that helps to organize event details that comprise simulations of future experiences. This kind of hypothesis implies strong interaction and interdependence between episodic and semantic knowledge during prospective thought (23).…”

The role of personal goals in autonoetic experience when imagining future events

“…Findings from cognitive, neuropsychological, and neuroimaging research have shown that episodic future thoughts are created based on informational components provided by episodic and semantic memory (i.e., specific past experiences and general knowledge about the world and the self), and multiple cognitive processes are engaged to retrieve, select, and assemble relevant pieces of information (for reviews, see D 'Argembeau, 2015;Irish & Piguet, 2013;Klein, 2013;Schacter et al, 2012).…”

The Role of Subjective Temporality in Future-Oriented Mental Time Travel

“…To anticipate our conclusions, we argue that although there is a marked tendency to treat FMTT as a unitary mental faculty that, despite task-driven outward variation, ultimately reduces to a common phenomenological state (underwritten primarily by episodic memory), FMTT is neither unitary nor is it necessarily beholden to episodic memory (on this latter point, see also Abraham & Bubic, 2015;Irish, Chapter 19 of this volume;Irish & Piguet, 2013;and Klein, 2103a). Rather, FMTT is diverse both in its experiential realizations and causal dependencies.…”