• Neither the cause of phantoms nor the associated suffering is well understood

• Phantoms have vivid sensory qualities and a precise location in space

• The phantom limb behaves like a normal limb

• Sometimes the amputee is sure the limb is stuck in some unusual position

• The reality of the phantom is also enhanced by wearing an artificial arm or leg

• Paraplegics: persons who have had a complete break of the spinal cord and therefore have no feeling in, or control over, their body below the break

• Paraplegics often have phantom legs and other body parts, including genitals

• As many as 70 percent of amputees suffer from pain

• Phantom limb pain usually starts shortly after amputation but sometimes appears weeks, months or years later

• Patients perceive the phantom limb as an integral part of the body

• Amputation is not essential for the occurrence of a phantom

• Brachial plexus avulsion: when all the nerves from the arm are ripped from the spinal cord

• If the eyes of someone with brachial plexus avulsion are closed, the phantom will remain in its original position when the real arm is moved by someone else

• Hypothesis 1 for phantom limb pain: the remaining nerves in the stump, which grow at the cut end into nodules called neuromas, continue to generate impulses. Following this, treatments for pain have attempted to halt the transmission of impulses at every level of the somatosensory projection system

• Neuroma activity cannot by itself account for either the phenomenon of the phantom limb or the suffering

• Hypothesis 2 for phantom limb pain: phantoms arise from the excessive, spontaneous firing of spinal cord neurons that have lost their normal sensory input from the body

• After sensory nerves in the body are cut, neurons in the spinal cord spontaneously generate a high level of electrical impulses, often in an abnormal, bursting pattern

• Hypothesis 3 for phantom limb pain: phantoms are caused by changes in the flow of signals through the somatosensory circuit in the brain

• Abnormally high levels of activity and a bursting pattern in cells of the thalamus in a paraplegic patient who had a full break of the spinal cord just below the neck but nonetheless suffered pain in the lower half of his body

Self-Awareness Neuromatrix

• Melzack argues that the brain contains a neuromatrix that, in addition to responding to sensory stimulation, continuously generates a characteristic pattern of impulses indicating that the body is intact and unequivocally one’s own

• Neurosignature: the pattern of impulses indicating that the body is intact and unequivocally one’s own

• 3 important neural circuits in the brain:

  • Sensory pathway passing through the thalamus to the somatosensory cortex

  • Pathways leading through the reticular formation of the brain stem to the limbic system

  • Cortical regions, including the parietal lobe, important to the recognition of the self and to the evaluation of sensory signals

• Patients who have suffered a lesion of the parietal lobe in one hemisphere have been known to push one of their own legs out of a hospital bed because they were convinced it belonged to a stranger

• The output carries information about sensory input as well as the assurance that the sensation is occurring in one’s own body

Genetically Prewired Matrix

• The specific neurosignature of an individual would be determined by the pattern of connectivity among neurons in the matrix

• The neuromatrix is an assembly whose connections are primarily determined not by experience but by the genes that could later be sculpted by experience

• Many people were born without an arm or a leg yet experience a vivid phantom

• The long-held belief that phantoms are experienced only when an amputation has occurred after the age of six or seven is not true

• In the absence of external stimuli, much the same range of experiences can be generated by other signals passing through the neuromatrix

• Phantoms do not usually disappear forever

• The formalin pain test found that an anesthetic block of the paw completely obliterates the late pain, but only if the anesthetic is delivered in time to prevent the early response. Once the early pain occurs, the drug only partly reduces the later response

• Pain can continue even after the nerves carrying pain signals are blocked, and this implies that long-lasting pain is determined not only by sensory stimulation during the discomfort but also by brain processes that persist without continual priming

Phantom Seeing and Hearing

• People whose vision has been impaired by cataracts or by the loss of a part of the visual processing system in the brain sometimes report highly detailed visual experiences

• Common phantom images include people and large buildings

• Phantom sights are not mere memories of earlier experiences; they often contain events, places or people that have never before been encountered

• Phantom seeing occurs most among the elderly, presumably because vision tends to deteriorate with age

• Phantom sounds are also extremely common

Phantom-Limb Pain

• The most common complaint is a burning sensation

• Half of those with persistent, long-term phantom pain fail to respond to any approach

• The brain does more than detect and analyze sensory inputs; it creates perceptual experience even in the absence of external inputs

• Altering the activity of pathways outside the somatosensory system might be important, either alone or in combination with other treatments

• Localized injection of lidocaine into diverse areas of the limbic system produces striking decreases in several types of experimentally produced pain in rats, including a model of phantom-limb pain

The Brain’s Body Image

• The neural networks for perceiving the body and its parts are built into the brain

• Phantom limbs become comprehensible once we recognize that the brain generates the experience of the body