As a child, did
you ever feel better after your mother kissed your bumped knee? How do you
think that worked? The power of suggestion—or the
placebo effect—is a powerful psychological phenomenon that affects
every aspect of our lives, dictating our preferences for food, drink,
medication, social activities, and more.
Pioneering
experiments describing the use of sham drugs date back to the late 18th century. A version
of John Quincy’s Lexicon Medicum published in 1811 defines the placebo as ‘an
epithet given to any medicine adapted more to please than to benefit the patient’.
However, physicians of the past tended to use forms of treatment that they
assumed were ineffective, as opposed to the modern day usage of inert
substances.
A wide variety
of conditions have been proven to be amenable to placebos, including depression,
sleep disorders, Parkinson’s disease, and pain2. The placebo effect has
been shown to impart tangible changes on the immune system similar to those who
received real medication, where patients given syrup had increased white blood
cell counts. Remarkably, patients with Parkinson’s
disease stopped experiencing tremors and muscle stiffness after
taking inert sugar pills. The success of mirror therapy in relieving phantom
pain in amputees can be thought of as another example of the power of
suggestion.
How our minds
are fooled is not fully understood. The placebo effect may be an evolutionary
adaptation that allows the brain to make quick decisions and assumptions about
the environment. Consider this: if we had to analyse every single stimulus that
our environment threws at us, we’d go mad in no time.
Scientists have
identified that the psychological mechanisms of the placebo effect lie in both
conscious expectations and learning. Although learning and expectations are not
mutually exclusive, they are heavily dependent on each other.
To explain,
when we expect a drug to reduce pain levels, our brains release endogenous endorphinsthat
in turn are responsible for alleviating pain. On the other hand, the learning
process involves integrating environmental and social cues in order to generate
an internal expectation and subsequent placebo response. Experiencing repeated
patterns of learning conditions (as in classical conditioning – think Pavlov’s
dogs), causes a person to respond in a way that has spill-over-effects effects
that influence unconscious physiological processes.
Multiple
studies have singled out the ventromedial prefrontal cortex (vmPFC) as a main
player in mediating the placebo effect. Other areas of significant importance
are the dorsolateral PFC, lateral orbitofrontal cortex, periaqueductal grey
area, rostroventral medulla, and nucleus accumbens-ventral striatum.
In short, the
complex underlying neuronal circuits involve the higher functioning areas of
the brain (frontal cortices) and the seat of unconscious processes such as
breathing, the brainstem. Interestingly, rsearch reports that the placebo
effect is absent in those with Alzheimer’s
disease (due to degeneration of the frontal cortex) and in
patients subjected to external suppression of frontal cortex function via
transcranial magnetic stimulation.
The endogenous opioid
system and its role in placebo-induced analgesia is perhaps the
best studied neurotransmitter system involved in the placebo effect. Naloxone,
an opioid receptor antagonist, has been found to nullify the effects of placebo
pain-killers. Other systems that have been implicated include the cannabinoid
system.
These
neuroanatomical and neurobiological findings likely have much room for growth
and refinement considering that different placebo responses have been found to
invoke different parts of the placebo circuit.
Given the
complicated psychological mechanisms behind the placebo, it comes as no
surprise that various factors are able to modulate its strength. Social context
has a real impact on the placebo effect, as it fosters preconceived notions
regarding treatment. For example, several trials showed that similar benefits
were experienced by both groups of patients who underwent either traditional or
sham Chinese
acupuncture (the latter involving superficial needling at non-acupuncture
points). The physician attitude and appearance of competency, as well as the
cost, branding, shape, size, color, and taste of the pills were able to affect
the perceived treatment efficacy.
It is common
beleif that one must be unaware of the placebo in order for the placebo effect
to work. Not so, argue a group of researchers from the University of Basel
(Switzerland) and Harvard Medical School. They demonstrated that participants
who were told that they were getting placebos and who received detailed
explanations of the placebo effect experienced significant relief from
heat-induced pain compared to those that were not told that they were given
bogus drugs.
These
surprising results underscore the formidable effects of the placebo effect and
how much more there is still left to learn. Furthermore, this study opens doors
to more ethically designed placebo-controlled studies. Withholding potentially
beneficial treatment from patients in placebo-controlled trials is considered
inherently unethical. However, with this study, it appears that full disclosure
may not be that different to the traditional practices of keeping placebo
patient groups in the dark.
In order to
manipulate the placebo effect for clinical benefit, the notion of placebo
responders and non-placebo responders was
investigated. Are some people more amenable to the power of suggestion than
others? If so, is it due to unchangeable genetic makeup or individual personality?
Other questions that come to mind regard the persistency of the placebo effect.
For how long does it last and does it transfer to other types of placebos? To
illustrate, will a person responding to placebo painkillers for pain relief
also respond to placebo antidepressants for improved moods?
In conclusion,
we know that the placebo is a strong weapon in the clinician’s armamentarium.
Despite that, the unpredictable variability of its effects obligates future
research that enables us to get a better understanding of exactly when and for
how long the placebo effect will work.
References:
de craen A,
Kaptchuk T, Tijssen J et al. Placebos and placebo effects in medicine:
historical overview. J R Soc Med. 1999;92:511-515. PMCID: PMC1297390
Price DD,
Finniss DG, Benedetti F. A comprehensive review of the placebo effect: recent
advances and current thought. Annu. Rev. Psychol. 2008. 59:565–90. doi:10.1146/annurev.psych.59.113006.095941
Colloca L,
Miller FG. How placebo responses are formed: a learning perspective.
Philosophical Transactions of the Royal Society B: Biological Sciences.
2011;366(1572):1859-1869. doi:10.1098/rstb.2010.0398.
Geuter S, Koban
L, Wager TD. The cognitive neuroscience of placebo effects: concepts,
predictions and physiology. Annu. Rev. Neurosci. 2017. 40:167–88. doi:10.1146/annurev-neuro-072116-031132.
Wager TD, Atlas
LY. The neuroscience of placebo effects: connecting context, learning and
health. Nat Rev Neurosci. 2015 Jul;16(7):403-18. doi:10.1038/nrn3976.
Miller FG,
Colloca L, Kaptchuk TJ. The placebo effect: illness and interpersonal healing.
Perspectives in biology and medicine. 2009;52(4):518. doi:10.1353/pbm.0.0115.
Buckalew LW,
Coffield KE. An investigation of drug expectancy as a function of capsule color
and size and preparation form. J Clin Psychopharmacol. 1982 Aug;2(4):245-8.
PMID: 7119132
Howe LC, Goyer,
J. P., & Crum, A. J. Harnessing the placebo effect: Exploring the influence
of physician characteristics on placebo response. Health Psychology.
2017;36(11):1074-82. doi:10.1037/hea0000499.
Locher C, Frey
Nascimento A, Kirsch I et al. Is the rationale more important than deception? A
randomized controlled trial of open-label placebo analgesia. Pain. 2017
Dec;158(12):2320-2328. doi:10.1097/j.pain.0000000000001012.
Image
via frolicsomepl/Pixabay.
http://brainblogger.com/2017/12/07/the-neuroscience-behind-the-placebo-effect/
No comments:
Post a Comment