Engram

Especially throughout the 20th century, philosophers, psychologists, and neurologists have tended to fiercely disagree about whether the brain and mind are modular and functions are localized (as in the caricature of 19th-century phrenologists) or whether it is more uniform and acts more globally, with its functions diffusely represented.

One contested aspect of brain function is memory: When one has a new memory, what changes in the brain? Where does the memory “go” in the brain? The engram (or “trace”) is the putative particular brain locus for memories. Based on the failure of his own lesion studies to find any such entity, the American neuropsychologist Karl Lashley, in his famous 1950 essay, “In Search of the Engram,” sides against localization and concludes that the engram is represented broadly throughout the brain.

One alternative explanation we may consider is that this difficulty in locating memories in the brain exists because memories are encoded in an immaterial mind and therefore would not alter the brain at all. This Cartesian dualistic notion is easily refuted by examples of patients who have changes in memory functioning by physical damage to their brains, or by the example of (physical) drugs that are given and subsequently alter the ability of a person to form or retrieve memories.

Modern scientific methods have allowed a more nuanced position than the either/or of the Lashley era and the dualism pervasive since Descartes, or possibly even earlier via the 11th century Islamic philosopher Ibn Sina. In contrast, the 2000 Nobel Prize in Medicine was given partially to Eric Kandel for his work demonstrating the molecular mechanisms of memory storage at neuronal synapses. These basic learning mechanisms seem to, in fact, be conserved among all animals. Further evidence that memories are created, stored, and retrieved by the actions of functionally differentiated brain regions was provided [Page 602]by the increasing evidence from the neuropsychology clinic. The famous patient H. M. had his medial temporal lobes removed (most importantly, his hippocampus) and subsequently could no longer form new long-term declarative memories. Additional evidence has shown that procedural memories (e.g., learning how to throw a curveball) are created and stored in a manner separate from declarative memories (e.g., remembering a phone number).

With the advance of modern cellular, molecular, and recombinant genetic methods of neurological research, the debate has somewhat resolved. Memory seems to have both definitive aspects of functional localization as well as diffuse representation: certain cortical and subcortical areas are absolutely crucial for nonpathological memory functioning, and yet many diffuse projections and interconnections exist between memory and other relevant brain regions.