Where is pain in the brain?

Abstract

Key argues that fish cannot experience pain based on (1) brain imaging in humans, (2) consequences of lesions and (3) direct brain stimulation. Imaging indeed shows that pain-relevant signals reach the cortex, but not that they underlie the subjective experience of pain. Lesions and stimulation data are more to the point, but Key paints an idiosyncratic and misleading picture of their effects. S1 and S2 ablation does not eliminate evoked or spontaneous pain, although there may be up-or down-modulation. Likewise, stimulation of pain-associated cortical areas rarely induces pain, and pain almost never occurs at the onset of epileptic seizures. In contrast, cortical lesions and activation do have striking and reliable effects on visual, auditory, smell and touch perception. Overall, the case for the cerebral cortex being an essential substrate for pain experience in humans is too equivocal a starting point for ruling out the possibility of pain experience in fish.