WIKIMEDIA, ROBIN_24Expectations give placebos their power, allowing them to dramatically alter our experience of a stimulus. Researchers demonstrate in Proceedings of the National Academy of Sciences today (October 14) that not only can placebos tamp down feelings of pain, they can also ramp up pleasurable sensations. It all depends on where a person starts. If she is expecting an improvement in pain, her sensory processing decreases. If, on the other hand, she anticipates a heightened sense of pleasure, then the sensory processing is magnified.
The researchers, led by Dan-Mikael Ellingsen at Gothenburg University in Sweden, offered a nasal spray placebo (supposedly containing oxytocin) or nothing at all to 30 study participants. On one day, the participants received gentle strokes on the left arm; on another day, a painful heat stimulus. In the pain scenario, the nasal spray was tied to a decrease in pain sensation, and in the pleasure scenario, it was associated with an increase in pleasure, compared to the times when the person was given no spray.
Using functional MRI, the researchers found increases in activity in the posterior insula and primary and secondary somatosensory areas—regions involved in sensory processing—during the pleasurable arm stroke placebo treatments. They also found decreases in these areas during the painful heat placebo sessions. These results suggest that a placebo can enhance good feelings by increasing sensory processing and squelch pain by decreasing sensory processing.
Interestingly, they also found that parts of the brain involved in reward and emotion, a network they called “emotion appraisal circuitry,” were activated in both the painful and pleasant situations. The researchers interpret this activation in both scenarios as having opposing regulatory effects on sensory processing. “Overall, our results suggest that emotion appraisal circuitry is recruited by expectations of a benefit, whether it is pain relief or enhanced pleasantness of a positive stimulus, and modulates sensory processing accordingly to meet these predictions.”
The research team says that focusing on both the pain-reducing abilities of placebos and the pleasure-enhancing abilities are important in clinical studies.