Cerebral representation of the subjective experience of pain in humans

A threat to the integrity of the organism by nociceptive stimulation activa tes multiple cerebral structures. The cerebral activation gives rise to a s ubjective experience of pain that comprises a sensory dimension (e.g, inten sity) and an affective dimension (e.g: unpleasantness). Brain imaging studi es using positron emission tomography (PET) in humans demonstrate a multifo cal and stereotyped pattern of activation in response to painful stimulatio n applied to the skin, muscle or viscera. The cortical activation is observ ed mainly in the contralateral hemisphere, in primary and secondary somatos ensory areas (S1 and S2), in the Insula of Reil, and in the anterior cingul ate cortex (ACC). Sub-cortical foci of activation are found in brain stem, thalamus, hypothalamus, lenticular nuclei, and cerebelum. The activity meas ured in cortical areas is proportional to the subjective experience of pain , and the modulation of the sensory or affective dimensions of pain by cogn itive interventions produces characteristic changes in cortical activity. A ctivity in ACC is larger following hypnotic suggestions to increase pain af fect than following suggestions to decrease pain affect. Similarly, activit y in S1 is larger following hypnotic suggestions to increase pain intensity than following suggestions to decrease pain intensity. Moreover, cerebral activity particularly in S1 and the perception of pain intensity, increase in parallel when attention is directed to the painful stimuli during a task of intensity discrimination, and decrease when attention is directed towar d concurrent auditory, stimulation. Pain is subserved by a vast network of cortical structures, each of which participates differently in the multiple aspects of the experience. Results of our studies suggest at least a parti al functional segregation of legions involved in the sensor-v and affective dimensions of pain.