The subjective experience of pain: where expectations become reality

Abstract

Our subjective sensory experiences are thought to be heavily shaped by interactions between expectations and incoming sensory information. However, the neural mechanisms supporting these interactions remain poorly understood. By using combined psychophysical and functional MRI techniques, brain activation related to the intensity of expected pain and experienced pain was characterized. As the magnitude of expected pain increased, activation increased in the thalamus, insula, prefrontal cortex, anterior cingulate cortex (ACC) and other brain regions. Pain-intensity-related brain activation was identified in a widely distributed set of brain regions but overlapped partially with expectation-related activation in regions, including the anterior insula and ACC. When expected pain was manipulated, expectations of decreased pain powerfully reduced both the subjective experience of pain and activation of pain-related brain regions, such as the primary somatosensory cortex, insular cortex, and ACC. These results confirm that a mental representation of an impending sensory event can significantly shape neural processes that underlie the formulation of the actual sensory experience and provide insight as to how positive expectations diminish the severity of chronic disease states.

Figures

Fig. 1.

Both expectation-related activation and pain-related activation were significantly related to the magnitude of expected and experienced pain intensity in correctly signaled trials (image left = right brain). Brain activation during expected pain overlaps extensively with activation during experienced pain.

Fig. 2.

Psychophysical ratings of experienced pain. (A) Expectations for decreased pain significantly reduce experienced pain (mean ± SD). Bars show significant differences (P < 0.01). (B) Differences in expected pain account for a significant percentage of the variability of the reduction in experienced pain (r2 = 0.85, P < 0.0002).

Fig. 3.

Expectations for decreased pain significantly reduce pain-related brain activation during 50°C stimulation (image left = right brain).

Fig. 4.

Brain regions where expectations for decreased pain significantly reduce pain-related (50°C) brain activation. Direct statistical comparisons between correctly and incorrectly signaled trials revealed that numerous sites (circled) exhibited pain-related activation when subjects expected a 48°C stimulus instead of a 50°C stimulus (image left = right brain).