Following the amputation of an extremity, nearly all patients experience an illusion that the missing limb is still present. Although this sensation usually diminishes over time, it persists in some degree throughout the amputee's life and can often be reactivated by injury to the stump or other perturbations. Such phantom sensations are not limited to amputated limbs; phantom breasts following mastectomy, phantom genitalia following castration, and phantoms of the entire lower body following spinal cord transection have all been reported. Phantoms are also common after local nerve block for surgery. During recovery from brachial plexus anesthesia, for example, it is common for the patient to experience a phantom arm, percieved as whole and intact, but displaced from the real arm. When the real arm is viewed, the phantom appears to jump into the arm and may emerge and reenter intermittently while the anesthesia wears off. These sensory phantoms demonstrate that the central machinery for processing somatic sensory information is not idle in the absence of peripheral stimuli; apparently, central sensory maps and processing systems continue to operate independently of the periphery.

Phantoms might simply be a curiosity -- or a provocative clue about higher-order somatic sensory processing -- were it not for the fact that a substantial number of amputees also develop phantom pain. This common problem is usually described as a tingling or burning sensation in the missing part. Sometimes, however, the sensation becomes a much more serious pain that patiences find increasingly debilitating. Phantom pain is, in fact, one of the more common causes chronic pain syndromes, a condition that is extraordinarily difficult to treat. Because of the relative independence of the central processing of pain, ablation of the spinothalamic tract, portions of the thalamus, or even primary sensory cortex does not generally relieve the discomfort felt by these patients.

I wonder... is this a "thing" or an "idea"?

Neuroscience, Sinaur Associates (QP355.2.N487 1997)

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