Donald Hebb’s work on the role of neurons in memory in some ways built on Aristotle’s idea of the mind as a blank slate at birth, with all memories imprinted through experience. Eric Kandel’s experiments on sea slugs helped concretize understanding of learning through molecular change and how neurotransmitters do their work.

In 1949, Donald Hebb formulated the theory that became known as Hebb’s Rule. His notion that “neurons that fire together, wire together” referred to the way that memories are encoded: as connections between neurons that are established with repeated use. Subsequent discoveries identified specific mechanics of memory consolidation and neural plasticity

Eric Kandel was a neurobiologist who worked particular with the sea slug Apylsia, with relatively few nerve cells that tend to be and thus easier to study. Its protective guard reflex for its gills also was a basis for studying learning mechanisms. Ultimately demonstrating Hebb’s rule, Kandel’s experiments identified the molecular changes occurring in learning as well as which neurotransmitters are involved. In 2000, Kandel, Arvid Carlsson, and Paul Greengard were awarded the Nobel Prize for Physiology or Medicine.