Sarah Robins (University of Kansas)
The idea that remembering involves a fixed engram, which becomes stable and permanent as a result of consolidation, has been a guiding assumption of the neuroscientific study of memory since its inception. Understanding of and commitment to the engram and consolidation has wavered more recently, as both systems and cellular neuroscientists have shifted to thinking of memory as a continuous and dynamic process. A central theme in 21st century neuroscience of memory is resistance to this traditional picture, with some calling for “the demise of the fixed trace” (Nadel, 2007) and others urging us to reject the “consolidation dogma” (Silva, 2007). One advantage of the traditional model of engrams and consolidation was that it offered clear identity conditions for the engram. The engram was identified functionally as (roughly) whatever neural change occurred as a result of learning and was uniquely implicated in subsequent behavior (Josselyn, Köhler, & Frankland, 2015). While there is a growing consensus that this traditional framework should be rejected, there is no accompanying agreement on how to modify our understanding of the engram. Proposed alternatives involve different ways of conceiving of engrams, not all of which can be true simultaneously. Proponents of reconsolidation suggest that consolidated engrams enter a new phase of vulnerability as a result of retrieval, incorporating new information (Nader & Hardt, 2009). So, on this view, an engram is the same engram over time so long as the same neurons are involved, even if the content/behavior/output produced by those neurons changes. Compare this to the standard consolidation model, whose proponents argue that the engram literally moves over time – from cells in the hippocampus to cells in the neocortex. On this view, the engram is the same engram over time so long as the content/behavior/output remains the same, even if the neurons responsible for producing it change. Which view is correct? The question cannot be resolved empirically. It requires reflection on our conceptual and theoretical commitments around the nature of memory and the role of the engram. In this paper, I apply the resources of contemporary philosophy of neuroscience and philosophy of memory to provide a framework in which the available avenues for theorizing about memory as a dynamic process can be understood.
