Inter-individual differences in pain processing investigated by functional magnetic resonance imaging of the brainstem and spinal cord.

The experience of pain is a highly complex and personal experience, characterized by tremendous inter-individual variability. The purpose of this study was to use functional magnetic resonance imaging (fMRI) to characterize responses in the brainstem and spinal cord to the same heat stimulus in healthy participants, to further our understanding of individual differences in pain perception. Responses to noxious heat stimuli at 49°C were investigated in 20 healthy individuals by means of fMRI of the brainstem and spinal cord, at 3 Tesla, and were compared with brain fMRI and quantitative sensory testing. Blood oxygenation-level dependent (BOLD) responses were detected with a general linear model (GLM) and effective connectivity was examined with structural equation modeling (SEM). Reported pain ratings ranged from 18 to 84/100 across the participants. Consistent with previous research, brain fMRI results show that BOLD responses in a number of cortical regions are correlated with individual pain ratings. Correlations between pain scores and BOLD responses are also demonstrated in the spinal cord dorsal horn, locus coeruleus, and thalamus. SEM results demonstrate the network of brainstem and spinal cord regions that contribute to the pain response, and reveal differences related to individual pain sensitivity. The results of this study are consistent with the conclusion that individual differences in pain perception in healthy participants are a consequence of differences in descending modulation of spinal nociceptive processes from brainstem regions.