1. Pain and some factors that modify it;Beecher;Anesthesiology,1951
2. Pain mechanisms: a new theory;Melzack;Science,1965
3. Operant conditioning in the treatment of chronic pain;Fordyce;Arch Phys Med Rehabil,1973
4. Pain terms: a list with definitions and notes on usage. Recommended by the IASP subcommittee on taxonomy;Pain,1979
5. Pain and suffering;Loeser;Clin J Pain,2000