Pain is an unpleasant sensation, and at the same time, it is always subjective and affective. Ten healthy subjects viewed 3 counterbalanced blocks of images from the International Affective Picture System: images showing painful events and those evoking emotions of fear and rest. They were instructed to imagine pain in their own body while viewing each image showing a painful event (the imagination of pain). Using functional magnetic resonance imaging, we compared cerebral hemodynamic responses during the imagination of pain with those to emotions of fear and rest. The results show that the imagination of pain is associated with increased activity in several brain regions involved in the pain-related neural network, notably the anterior cingulate cortex (ACC), right anterior insula, cerebellum, posterior parietal cortex, and secondary somatosensory cortex region, whereas increased activity in the ACC and amygdala is associated with the viewing of images evoking fear. Our results indicate that the imagination of pain even without physical injury engages the cortical representations of the pain-related neural network more specifically than emotions of fear and rest; it also engages the common representation (i.e., in ACC) between the imagination of pain and the emotion of fear.

We investigated the brain activation associated with sweet taste-induced analgesia by 3-T functional magnetic resonance imaging, the mechanism of which is considered to involve the central nervous system. After 12 healthy individuals ingested tasteless gelatin (nonsweet condition) or sweet glucose (sweet condition) in a magnetic resonance imaging scanning gantry, the cold pressor test was applied to their medial forearm. Under both conditions, the cold pressor test robustly activated the pain-related neural network, notably the anterior cingulate cortex, insula, posterior parietal cortex, and thalamus, although such activations under the sweet condition weakened with pain threshold increase, compared with those under the nonsweet condition. Together with emotional changes in pain appraisal, our findings provide objective representation of sweet taste-induced analgesia in the human brain.

The human pain system contains a somatotopical representation in SI but with less somatotopical organization in the secondary somatosensory cortex. The current results provide supporting evidence of SI involvement in human pain perception and suggest that human SI subserves the localization of the stimulated site in nociceptive processing.

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Romantic relationship, a widespread feature of human society, is one of the most influential factors in daily life. Although stimuli related to romantic love or being in a romantic relationship commonly result in enhancement of activation or functional connectivity of the reward system, including the striatum, the structure underlying romantic relationship-related regions remain unclear. Because individual experiences can alter gray matter within the adult human brain, we hypothesized that romantic relationship is associated with structural differences in the striatum related to the positive subjective experience of being in a romantic relationship. Because intimate romantic relationships contribute to perceived subjective happiness, this subjective enhancement of happiness might be accompanied by the experience of positive events related to being in a romantic relationship. To test this hypothesis and elucidate the structure involved, we compared subjective happiness, an indirect measure of the existence of positive experiences caused by being in a romantic relationship, of participants with or without romantic partners (N = 68). Furthermore, we also conducted a voxel-based morphometry study of the effects of being in a romantic relationship (N = 113). Being in a romantic relationship was associated with greater subjective happiness and reduced gray matter density within the right dorsal striatum. These results suggest that being in a romantic relationship enhances perceived subjective happiness via positive experiences. Furthermore, the observed reduction in gray matter density in the right dorsal striatum may reflect an increase in saliency of social reward within a romantic relationship. Thus, being in a romantic relationship is associated with positive experiences and a reduction of gray matter density in the right dorsal striatum, representing a modulation of social reward.