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A pair of studies in the current Science demonstrate that placebo or the mere expectation of relief, without treatment, can cause physical changes in how the brain responds to pain. In the two studies, researchers used functional magnetic resonance imaging (fMRI) to map blood flow changes in the brains of volunteers. In one study, the volunteers received harmless but occasionally painful electric shocks or heat. They were then given a placebo anti-pain cream.When they rated the pain as less intense--and the pain circuits in their brain showed less activity.
These studies from Michigan and Princeton show that the prefrontal cortex is active in the placebo response. Images from this research are the first to show how the prefrontal cortex is activated by the expectation of pain relief, and the way that this can in turn trigger a reduction of activity in the thalamus, somatosensory cortex, and other parts of the cerebral cortex - areas responsible for sensing pain.
Empathy
Our ability to have an experience of another's pain is characteristic of empathy. In the second study, empathy for another person's pain was evaluated and clearly showed that we use many of the same brain areas that are activated by our own experience of pain.
Brain activity was measured in both volunteers receiving a painful stimulus and in others observing a loved one who was receiving a similar painful stimulus. Bilateral anterior insula (AI), rostral anterior cingulate cortex (ACC), brainstem, and cerebellum were activated when subjects received pain and also by a signal that a loved one experienced pain. AI and ACC activation correlated with individual empathy scores. Activity in the posterior insula/secondary somatosensory cortex, the sensorimotor cortex (SI/MI), and the caudal ACC was specific to receiving pain. The researchers conclude that in empathy, only part of the pain network and not the entire pain matrix was associated with its affective qualities as opposed to its sensory qualities. These are the so called second-order re-representations containing the subjective affective dimension of pain. It is proposed that these cortical re-representations have a dual function - one to form the basis of our ability to form subjective representation of feelings that allow us to predict the effects of emotional stimuli with respect to the self and two, they serve as a neural basis for our ability to understand the emotional importance of a particular stimulus for another person and to predict its likely associated consequences. Their data suggests that our ability to empathize has evolved from a system for representing our internal bodily states and subjective feeling states.
Additional reading on placebo effects
Placebo Research at the UCLS Neuropsychiatric Institute
The Healing Power of Placebos
US Food and Drug Administration Article
The power of placebo
BMJ Editorial
Placebo Effect: The Power of the Sugar Pill
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