Memory Traces and Engrams

Philosophers posit memory traces as mental states required for remembering, while neuroscientists appeal to engrams as the neural mechanism for retaining information in the brain. Developments in the philosophy of memory and in neurobiology have led to increased attention to memory traces and engrams, respectively, in recent years—and a collective tendency, across both fields, to use memory trace and engram interchangeably. This suggests their relationship is settled. I argue that it is not. Conflating memory traces and engrams has obscured important conceptual questions and slowed progress toward understanding either. After sketching the problem, I focus on the engram as a scientific concept. While many neurobiologists have long assumed that there are engrams, it is only recently, with the advent of tools like optogenetics, that it’s been possible to identify them. Engram is thus something of a comeback concept, arguably far more popular now than at any point since its inception. This places it at a unique intersection of questions about enduring scientific concepts (atom, gene) and conceptual innovation in contemporary neuroscience. I use this framing to identify three distinct concepts of the engram operating in contemporary neuroscience, only one of which aligns with the memory trace.