Sensations evoked in patients with amputation from watching an individual whose corresponding intact limb is being touched.

BACKGROUND

After amputation of a limb, the majority of patients experience phantom sensations, such as phantom pain. Such patients provide an opportunity for the exploration of the perceptual correlates of recently discovered "mirror neurons," which fire not only when individuals move their own limb but when they watch the movements of the corresponding limb of another person. Similar neurons exist in the secondary somatosensory cortex for touch: they fire when the individual is touched or simply watches another person be touched. While these neurons cannot by themselves discriminate between the two, the mind is aware of the difference between feeling and watching; one does not confuse empathy with actual experience.

OBJECTIVE

To investigate whether patients with amputation experience the sensations of another person in their own phantom limb during the mere observation of someone else being touched, owing to removal of the inhibition of the mirror neuron system that would have occurred had the limb been intact.

DESIGN

Case report.

SETTING

University campus, academic setting. Patients Four patients with upper-limb amputation.

MAIN OUTCOME MEASURES: The subjective reports of patients.

RESULTS

We report that 4 individuals with arm amputation, the mere watching of the intact hand of another being touched evokes vivid, precisely localized sensations in their own phantom hands.

CONCLUSIONS

We suggest these evoked sensations are owing to removal of neural signals from the hand that would have ordinarily inhibited the response of the mirror neurons and prevented their activity from reaching the threshold of conscious awareness.