In this particular limited volume (a hundred and ten web pages, the rest is made up of glossaries and descriptions of other LRH books), Hubbard describes how he allegedly found the "reactive head" and also the "engrams" https://lululomn118383.onesmablog.com/the-fact-about-dianetics-the-modern-science-of-mental-health-that-no-one-is-suggesting-69663924