Phantom Limbs: A Neurobiological Explanation Essay

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Phantom Limbs: A Neurobiological Explanation

Severely injuring a digit or limb can result in unrepentant damage and amputation. However, the painful sensations experienced in regard to that limb do not necessarily cease after amputation. The concept of feeling sensations in a limb that is no longer attached to the body is referred to as feeling a "phantom limb." This phenomenon is experienced by approximately 80%-100% of all patients who have lost a limb (1), and has therefore sparked wide interest in scientific community.

Phantom limb sensations are common for people with missing limbs or digits. In most cases, a phantom arm hangs straight down at the side when the person sits or stands (2). The subject feels as though the limb is
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However, if the leg is no longer attached to the body, then how can the neurons in the leg transport signals to the nervous system in order for the body to feel sensations?

One possible explanation is the existence of neurons from the phantom limb even after amputation. Even though the neuron's axons were cut, the neurons could still be present due to regeneration of broken axons. This would allow for an action potential to travel back to the spinal cord even though the leg itself is no longer attached. The sensory neurons are still in tact with the central nervous system and the body can therefore still feel sensations coming from the missing limb (4).

A study was performed by Merzenich in 1986 in which the index finger of a monkey was amputated, and signals were monitored in the corresponding part of the monkey's corticol map (3). Since the monkey's finger was no longer attached to the body, the logical hypothesis is that there would be no signals coming from the finger's area to the nervous system. However, every time the two fingers adjacent to that of the amputated one were touched, there were nerve impulses in the spinal cord. This led the scientists to believe that there are existing axon branches that become unbranched after normal input ends.
Similarly, Pons et al. demonstrated in 1991 that in adult monkeys in which one or more arms had been removed, the

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