Neural correlates of interindividual differences in the subjective experience of pain

Abstract

Some individuals claim that they are very sensitive to pain, whereas others say that they tolerate pain well. Yet, it is difficult to determine whether such subjective reports reflect true interindividual experiential differences. Using psychophysical ratings to define pain sensitivity and functional magnetic resonance imaging to assess brain activity, we found that highly sensitive individuals exhibited more frequent and more robust pain-induced activation of the primary somatosensory cortex, anterior cingulate cortex, and prefrontal cortex than did insensitive individuals. By identifying objective neural correlates of subjective differences, these findings validate the utility of introspection and subjective reporting as a means of communicating a first-person experience.

Fig. 1.

The distribution of pain intensity ratings obtained during functional MRI scanning shows that the subjective experience of pain intensity evoked by a 49°C stimulus differed markedly across individuals. The horizontal bar indicates the median of all 17 individuals.

Fig. 2.

Brain regions displaying different frequencies of activation between high- and low-sensitivity subgroups. Circles are centered on regions where the peak differences between groups were located. Colors in A and C correspond to the number of individuals displaying statistically significant activation at a given voxel (frequency), whereas colors in B and D correspond to the z-score of the subgroup analysis. Slice locations in A and B are -2 mm from the midline, whereas slice locations in B and C are 32 mm from the midline (in standard stereotaxic space). Structural MRI data (gray) are averaged across all individuals involved in corresponding functional analysis.

Fig. 3.

Pain-evoked thalamic activation displayed no significant differences between high- and low-sensitivity subgroups. Both high-sensitivity (left image) and low-sensitivity (center image) subgroups exhibited statistically significant activation of the contralateral (left) thalamus (denoted by a circle). Slices are located -20 mm from the anterior commissure.