title: Expectancy and Conditioning in Placebo Analgesia: Separate or Connected Processes?
abstract: Expectancy and conditioning are often tested as opposing explanations of placebo analgesia, most commonly by pitting the effects of a conditioning procedure against those of a verbally-induced expectation for pain reduction. However, conditioning procedures can also alter expectations, such that the effect of conditioning on pain might be mediated by expectancy. We assessed the effect of conditioning on expected pain and placebo-induced pain reduction. Participants were told that the treatment (real or sham acupuncture) would affect one side of the arm but not the other. Because a real acupuncture effect would not be specific to a randomly selected side of the arm, any difference in pain between the "treated" and the "untreated" side would be a placebo effect. There were no significant main effects or interactions associated with type of acupuncture (real versus sham). In both groups, conditioning decreased expected pain for "treated" location and also increased the placebo effect (i.e., the difference in pain report between "treated" and "untreated" locations). In addition, mediation analysis lent support to the hypothesis that the effects of conditioning on placebo analgesia may be mediated by expectancy, although the size of this indirect effect requires further study.
authors.affiliation: Harvard Medical School, Beth Israel Deaconess Medical Center, University of Plymouth.
authors.forename: Irving
authors.initials: I
authors.lastname: Kirsch
authors.affiliation: Harvard Medical School, Massachusetts General Hospital.
authors.forename: Jian
authors.initials: J
authors.lastname: Kong
authors.affiliation: Wilfrid Laurier University.
authors.forename: Pamela
authors.initials: P
authors.lastname: Sadler
authors.affiliation: Massachusetts General Hospital.
authors.forename: Rosa
authors.initials: R
authors.lastname: Spaeth
authors.affiliation: Northwestern University.
authors.forename: Amanda
authors.initials: A
authors.lastname: Cook
authors.affiliation: Harvard Medical School, Beth Israel Deaconess Medical Center.
authors.forename: Ted
authors.initials: T
authors.lastname: Kaptchuk
authors.affiliation: Harvard Medical School, Massachusetts General Hospital.
authors.forename: Randy
authors.initials: R
authors.lastname: Gollub
references.citation: Pain. 1978 Jun;5(1):19-29
references.pmid: 673439
references.citation: Pain. 2007 Mar;128(1-2):31-9
references.pmid: 17030095
references.citation: Lancet Neurol. 2004 Nov;3(11):679-84
references.pmid: 15488461
references.citation: J Neurosci. 2008 Dec 3;28(49):13354-62
references.pmid: 19052227
references.citation: Science. 2004 Feb 20;303(5661):1162-7
references.pmid: 14976306
references.citation: Pain. 2013 Mar;154(3):459-467
references.pmid: 23352757
references.citation: Pain. 1978 Jun;5(1):5-18
references.pmid: 673440
references.citation: Pain. 1990 Oct;43(1):121-128
references.pmid: 2277714
references.citation: Science. 1983 Jan 28;219(4583):400-5
references.pmid: 6294833
references.citation: Psychol Bull. 2004 Mar;130(2):324-40
references.pmid: 14979775
references.citation: J Pain. 2005 Jan;6(1):55-64
references.pmid: 15629419
references.citation: Psychol Methods. 2002 Mar;7(1):83-104
references.pmid: 11928892
references.citation: J Psychosom Res. 2009 Apr;66(4):323-8
references.pmid: 19302890
references.citation: Lancet. 1998 Aug 1;352(9125):364-5
references.pmid: 9717924
references.citation: Proc Natl Acad Sci U S A. 2012 Sep 25;109(39):15959-64
references.pmid: 23019380
references.citation: Pain. 1997 Aug;72(1-2):107-13
references.pmid: 9272794
references.citation: J Neurosci. 2005 Nov 9;25(45):10390-402
references.pmid: 16280578
references.citation: J Pers Soc Psychol. 1985 Jan;48(1):47-53
references.pmid: 3981392
references.citation: Nature. 1988 Dec 22-29;336(6201):766-7
references.pmid: 3205302
references.citation: Neuroimage. 2009 Apr 15;45(3):940-9
references.pmid: 19159691
references.citation: Pain. 2008 May;136(1-2):211-8
references.pmid: 18372113
references.citation: Am Psychol. 1988 Mar;43(3):151-60
references.pmid: 3364852
references.citation: Neuroreport. 2007 May 28;18(8):771-5
references.pmid: 17471064
references.citation: Pain. 2009 Jul;144(1-2):28-34
references.pmid: 19278785
references.citation: Pain. 2003 Dec;106(3):401-409
references.pmid: 14659523
references.citation: Neuroimage. 2009 Sep;47(3):1066-76
references.pmid: 19501656
references.citation: Pain. 2006 Dec 15;126(1-3):115-22
references.pmid: 16890357
references.citation: Psychol Sci. 2013 Oct;24(10):1918-27
references.pmid: 23955356
references.citation: J Neurosci. 2003 May 15;23(10):4315-23
references.pmid: 12764120
references.citation: Psychol Methods. 2002 Dec;7(4):422-45
references.pmid: 12530702
references.citation: Pain. 1999 Nov;83(2):147-56
references.pmid: 10534585
references.citation: Pain. 2002 Apr;96(3):393-402
references.pmid: 11973014
references.citation: Philos Trans R Soc Lond B Biol Sci. 2011 Jun 27;366(1572):1859-69
references.pmid: 21576143
references.citation: J Neurosci. 2006 Jan 11;26(2):381-8
references.pmid: 16407533
references.citation: PLoS One. 2012;7(3):e33400
references.pmid: 22457759
references.citation: Acupunct Med. 2007 Jun;25(1-2):36-40
references.pmid: 17641566
references.citation: Pain. 1999 Nov;83(2):235-41
references.pmid: 10534595