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Papers of the Week

Papers: 11 May 2019 - 17 May 2019


Human Studies

2019 Jan-Jul

Neurobiol Pain


Is placebo analgesia for heat pain a sensory effect? An exploratory study on minimizing the influence of response bias.


Case LK, Laubacher CM, Richards EA, Grossman M, Atlas LY, Parker S, Bushnell CM
Neurobiol Pain. 2019 Jan-Jul; 5.
PMID: 31080912.


We explored the ongoing question of whether placebo analgesia alters afferent nociceptive processing in a novel paradigm designed to minimize the role of response bias in placebo measurement. First, healthy adult participants received a standard heat placebo induction and conditioning procedure using a topical "analgesic" cream applied to one arm. During a subsequent placebo testing procedure, participants rated stimuli on the placebo-treated arm and untreated arm, using a task that minimized subjects' ability to guess the expected response, thus reducing experimenter demand. Retrospectively participants reported moderate analgesia effectiveness (mean=5.3/10), but for individual temperature ratings, only 2 subjects exhibited a perceptual placebo response >5 points. Next, these subjects completed a novel, exploratory task designed to measure changes in inter-arm in discriminative accuracy that would be expected from changes in afferent nociception. Both placebo responders (but no non-responders) showed reduced discriminative ability when the hotter stimulus occurred on the placebo arm, an effect consistent with alterations in nociceptive afferent flow and unlikely to be caused by response bias.