Ricciardi and Umezawa proposed in 1967 a general theory of quanta of long-range coherent waves within and between brain cells, and showed a possible mechanism of memory storage and retrieval in terms of Nambu–Goldstone bosons. This was later developed into a theory encompassing all biological cells and systems in the quantum biodynamics of Del Giudice and co-authors. Mari Jibu and Kunio Yasue later popularized these results and discussed the implications towards consciousness.