Is pain in the brain?

There has been much interest in pioneering neuroimaging experiments that study brain responses to sensory stimulation in patients in a minimally conscious or persistent vegetative state. Here, we discuss a recent study by Melanie Boly and her colleagues, in which brain responses to stimulation of the median nerve were measured by use of PET in healthy volunteers and in patients in either a minimally conscious or persistent vegetative state. The stimulation was considered to be painful by the volunteers but did not elicit behavioral responses in either of the two patient groups. Nevertheless, brain activation in patients in a minimally conscious (but not persistent vegetative) state was seen in areas very similar to those activated by the stimuli judged to be painful in healthy volunteers. Here, we discuss whether such data can be used to conclude that individuals with severe brain damage feel pain, and we consider the ethically appropriate clinical response to such important new data.