In psychoanalysis, psychic energy in the secondary process, contained and accumulating within particular groups of neurons, its flow being subject to checks and controls through binding. Sigmund Freud (1856–1939) attributed the concept to the Austrian physician Josef Breuer (1842–1925), but Breuer, although he discussed a related concept, never used the term, and the version of the concept that Freud published in 1895 in his ‘Project for a Scientific Psychology’ (Standard Edition, I, pp. 177–397) is quite different from Breuer's, although both based their notions on the principle of constancy. See also nirvana principle, reality principle. Compare free energy.