- analgesia: inability to feel pain
- determinants of the analgesic efficacy of a placebo are:
o presence of sensory cues associated with effective treatment or pain relief in
the past
o expectation of pain relief
- placebo implies a mismatch between what patient expects and the treatment’s
actual intrinsic efficacy
- placebo effect can occur in several situations: with deception, with conscious
expectations, following conditioning, associated with psychosocial context
Terminology
- placebo: dummy treatment such as sham surgery and sugar pill
- placebo effect: observable difference between groups that is attributable to the
efficacy of the placebo (e.g. difference in mean treatment effect between groups)
- placebo analgesic response: pain relief in an individual that results from the
expectation of effectiveness of therapeutic intervention
Active placebo responses vs statistical artifacts:
- patients in placebo groups can improve for several reasons:
o improvement would have happened w/ treatment bc of history of disease
o patients tend to enroll when the pain is worst, improvement can be a
consequence of regression to mean
o patients benefit from the positive psychosocial context of being in a study
(more attention, additional social support)
Evidence for placebo analgesia
Placebo effects in experimental and clinical studies
- “clinical trials” report larger effect sizes (compared to experimental)
- most convincing evidence is seen for low back pain and IBS
- placebo effects are larger with sustained pain and in the presence of hyperalgesia
- enthusiasm of physician, verbal communication, conditioning effects from previous
exposure, and physical properties of the placebo and how it’s administered are
critical factors
Cognitive bias as a source of placebo effects
- patients can establish a lower anchor point for pain
- patients can overweigh moments with lower pain to match expectations
- patients may desire report what they believe experimenter expects
- patients may desire to be consistent with previous behavior
- patients may bias their reports towards what they would like to happen
- although placebo treatment decreases reported pain, it doesn’t affect sensory
discriminability
, Placebo effects on brain correlates of pain
- studies show that with placebo treatment:
o reductions in pain-related activity in most brain correlates of pain experience
o activation of areas and circuits important for modulation of pain
o activation of the endogenous opioid and dopamine systems
- placebo effects on fMRI responses to noxious stimuli
o reduced processing of noxious somatic stimuli with placebo treatment
o placebo induced reductions in contralateral anterior insula, medial thalamus
and rostral dorsal anterior cingulate (rdACC) accompanying large behavioral
placebo effects
- placebo effects on event-related potential responses to noxious stimuli
o evidence against a habituation related explanation for the placebo effects
o placebo treatments can modulate responses to early nociceptive processes
- placebo effects on spinal nociceptive processes
o limited direct evidence for spinal inhibition
o placebo treatment significantly reduced spinal fMRI activity in response to
heat
Ingredients of placebo analgesia: what makes a placebo responder?
- promising psychological correlates of placebo response include: suggestibility,
optimism, expectation, behavioral activation, desire for relief, reductions in
anticipatory anxiety, sensitivity to opiate drugs
- placebo effects are influenced both by individual differences and experiences with
treatments, context and cues
- conditioning: process of learning that drug cues signal pain relief or drug-induced
changes in the brain’s neurochemistry
- conditioning can work in at least 2 ways:
o by eliciting conscious expectations of drug relief
o by brain mechanisms independent of conscious expectations
- nocebo effect: conditioning can also produce negative expectations and brain
changes that increase pain
- nocebo instructions have larger and longer-lasting effects than placebo instructions
and produce stronger physiological responses such as on cortisol
Mechanisms of placebo analgesia
Engagement of the evaluative and visceromotor brain systems
- consistent increases in placebo conditions are found in: bilateral posterior
dorsolateral prefrontal cortex (DLPFC), anterior prefrontal cortex, orbitofrontal
cortex (OFC), the pre-genual anterior cingulate cortex (pgACC) and the midbrain
periaqueductal gray (PAG)
- these regions form a control circuit that generate expectations of pain relief and alter
appraisals of ongoing pain
- involvement of PAG points to possible activation of descending control systems and
altered affective-motivational states
- strongest links during anticipation of pain were found in the anterior prefrontal
cortex and superior parietal cortex
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller ebru1365. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $4.31. You're not tied to anything after your purchase.