Toward A Quantitative View of the Engram

Abstract

The qualitative nature of memory remains unknown, but common experience and laboratory observations attest to its quantitative character. Memories may be "strong" or "weak," as judged subjectively or as inferred from animal experiments. The typical experimental measure of a memory is the probability of emission of a learned behavioral response, the observable indicant of the memory. Each indicant is considered to reflect a corresponding memory trace in the brain, the so-called engram. The indicant is quantified, but the corresponding engram is not. This dichotomy adds a conceptual gap to the physiological gap that separates an engram from its indicant. There is a need for language to describe the engram in a quantitative sense, in order to link it more definitely with its measured indicant. It seems timely to introduce a quantitative unit of memory, even though such a unit must as yet be hypothetical, speculative, and tentative.