The largest ever brain scan study of the placebo effect has revealed that it seems to act on systems in the brain that process the emotional aspects of pain, which could explain why sugar pills can ease discomfort.
Expectations, suggestion and social cues can all influence the placebo effect, where a person鈥檚 symptoms lessen after taking a dummy medicine that they believe to be an effective treatment. But how this affects the sensory pathways that transmit pain signals in the brain is unclear.
To learn more, at Dartmouth College in New Hampshire and her colleagues delivered moderately painful heat to nearly 400 people鈥檚 fingers via an electrode, allowing them to become familiar with this sensation.
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They then applied two creams to different fingers of each participant鈥檚 left hand. One was labelled 鈥淧rodicaine, an effective pain-relieving drug鈥� and the other 鈥渁 control cream with no effects鈥�. The two creams were, in fact, identical, with neither containing a pain-relieving drug.
Before receiving the Prodicaine cream, participants watched a short video on how to use it, along with a fake testimonial about how effective it is. They were also told about its potential side effects.
The researchers then reapplied the heat, this time alongside painful pressure. During this, they scanned the participants鈥� brains via magnetic resonance imaging (MRI).
The participants reported experiencing less pain in the fingers treated with what they believed to be Prodicaine cream than in those treated with the cream labelled as a control. The Prodicaine cream not only influenced their perception of the heat pain that they had become somewhat accustomed to, but also of the mechanical pain they hadn鈥檛 experienced before.
鈥淭his study addressed an important, unanswered question about transfer of placebo effects,鈥� say the researchers. Previous studies have suggested that the effect doesn鈥檛 always carry over between different types of pain, such as from labour pain to postpartum pain. 鈥淥ur findings indicate robust behavioral placebo effects that are generalizable to new outcomes,鈥� they say.
Turning to the brain scans, the researchers looked at responses in a network of systems that they refer to as the 鈥渘eurologic pain signature鈥�, .
The Prodicaine cream had no effect on neural activity in this network, but it did decrease activity in another network involving 鈥渕eaning-making systems鈥�, such as the regulation of emotions.
bioRxiv
