Chapter 7 The role of secondary somatosensory cortex and insula in pain

Abstract

The opercular and insular cortex areas usually represent the primary pain areas in the human brain, mostly involved in the sensory-discriminative analysis of pain sensation while other areas, principally the cingulate gyrus and orbito-frontal cortex, are thought to be involved in the affective reaction to pain. This chapter discusses the recent contribution of neuroimaging studies, scalp and intracortical pain evoked potentials, and direct brain stimulation in humans in evaluating the role played by secondary somatosensory cortex and insula in pain. Positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have provided relevant data for the spatial localization of pain-related responses in the brain. The blood oxygenation level- dependent (BOLD) signal measured in fMRI activation studies reflects changes in cerebral blood flow (CBF) and deoxyhemoglobin blood content induced by pain. Studies comparing fMRI with PET pain activation have shown that, in response to pain, the increased BOLD signal is usually located in more superficial positions than the CBF increase. This discrepancy reflects the general trend for BOLD signal changes to minimize or mask deep brain signal changes.