The pivotal role of semantic memory in remembering the past and imagining the future

Episodic memory refers to a complex and multifaceted process which enables the retrival 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 susbtrates. 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 forfusing on neurodegenerative populations which proved revelatory for our understanding of the complex interplay between espisodic and semantic memory. Whereas episodic memory research has traditionally focused on retrieval of autobiograpical events fromt the past, we also include evidence from the recent paradigm shift in which episodic memory is viewed as an adaptive and contructive process which facilitates the imaging 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 ot contend that semantic processing may underline most, if not forms of episodic memory, irrespective of temporal condition.