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Essay Name       : 672.txt 
Uploader         : Ann Zlatin
Email Address    : 
Language         : English
Subject          : Health
Title            : Phantom limb phenomena
Grade            : 90%
School System    : college
Country          : usa
Author Comments  : 
Teacher Comments : 
Date             : jan 96
Site found at    : 
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	For  more than a hundred years, physicians have published accounts of people who perceive an amputated arm or leg as if it were still there.  Many amputees feel burning, cramping, or shooting pains in these phantom limbs.
Doctors explained this by saying that the patients went through a denial period due to the trauma of loosing a body-part. Experts  have discovered
in the last decade that the sensations which the amputees have been reporting,
is due to a manifestation called Phantom limb phenomena.
	The neurobiologists have been chasing the phantom. Their first attempts were to figure out were do the  sensations originate. When a limb is amputated, the severed nerves that formerly carried messages of touch , temperature, and pain from the skin, form  nodules on their cut ends, called neuromas. For years, the favored explanation was, that the cut nerve endings continue to send impulses up the spinal cord to the brain. This explanation was repealed when  the neurosurgeons cut just above the neuromas. The proof was in the fact that the relief was temporary and therefore that the sensation  must be emanating from the brain. The discovery, that  the sense of touch emanates from our heads rather than our fingertips, leads the researchers onto a new dimension  in neuroscience. 
	It is known to us that  when the receptors of the neurons are stimulated, an electrical impulse is generated. It travels through the spinal cord, to the brain stem. This electrical  impulse travels further to the relay station – thalamus, and from there to the somatosensory cortex. This area has been accurately mapped out. Each area of skin has its lot in the cortex. The more receptors active in an area of  skin, the bigger will be its allotment.  With this in mind, scientists outlined the diagram of correlation between the areas of the body and cortex. For example, the hands would have a significantly larger representation, then the back. They constructed a model of  a greatly exaggerated person drawn out on the surface of the brain, a homunculus. 	
	



The scientists are now challenging the theory of brain plasticity. It has been always believed that the brain is plastic during infancy, but after this   critical period of flexible growth, the brain’s nueronal circuitry becomes hardwired. The homunculus was believed to be part of that hardwired system.  Therefore, once a limb is amputated, the allotted area in the cortex should be forever silent. 
	Since the 1960s, neuroscientists have been doing experiments which help us understand what help us understand what is happening in the brain of an amputee who is experiencing the phantom limb pain. Two of the most  prominent  of these experimenters  are Michael Merzenitch  and Timothy Pons.
	In 1980s, Michael Merzenich and his colleagues initiated a study in this field. They worked on a series of experiments which produce curious results. In one such experiment, they amputated a finger of an adult monkey. After a few weeks, they read the signals  of the monkey’s cortex. The expected results was for the hardwired brain ( in the area of the missing finger) to be silent. They were amazed to find that the neurons within the region, fired, each time the adjacent fingers were touched. They explained this by the fact that the remapping was  only a millimeter or two,  not significant amount because that is the approximate length of a neuronal axon. The explanation (one which would not demolish the "hardwired brain theory") was that the existing, unused branches of the axons were ready in contact across the borders of the cortical regions. When normal input from one amputated finger ceased, these dormant connections were invading the vacated region, but only as far as an axon could reach.
In 1991, Timothy Pons experimented on a group of macaques that, in an  unrelated experiment, 12 years earlier, had had the sensory nerves from one arm cut where they entered the spinal cord.  Pons attached electrodes in the cortexes of the monkeys, to investigate what has 12 years of  dormancy had done to the part of the monkeys’ homunculus, where the  limbs have been unplugged. Expecting to find just a few millimeters of encroachment, he was shocked to find the face region had completely invaded the neighboring cortex. In all four animals that were studied, the entire hand and arm region responded when the face was stimulated.
 	Because the numbed limb was not sending any messages  to the cortex, a massive remapping occurred.  Pons explains that in the thalamus, location of the chin and arm lots are next to each other. When the arm stops sending mesages to the  cortex, the chin takes over.









	What is  the  pu

























































	For  more than a hundred years, physicians have published accounts of people who perceive an amputated arm or leg as if it were still there.  Many amputees feel burning, cramping, or shooting pains in these phantom limbs.
Doctors explained this by saying that the patients went through a denial period due to the trauma of loosing a body-part. Experts  have discovered
in the last decade that the sensations which the amputees have been reporting,
is due to a manifestation called Phantom limb phenomena.
	The neurobiologists have been chasing the phantom. Their first attempts were to figure out were do the  sensations originate. When a limb is amputated, the severed nerves that formerly carried messages of touch , temperature, and pain from the skin, form  nodules on their cut ends, called neuromas. For years, the favored explanation was, that the cut nerve endings continue to send impulses up the spinal cord to the brain. This explanation was repealed when  the neurosurgeons cut just above the neuromas. The proof was in the fact that the relief was temporary and therefore that the sensation  must be emanating from the brain. The discovery, that  the sense of touch emanates from our heads rather than our fingertips, leads the researchers onto a new dimension  in neuroscience. 
	It is known to us that  when the receptors of the neurons are stimulated, an electrical impulse is generated. It travels through the spinal cord, to the brain stem. This electrical  impulse travels further to the relay station – thalamus, and from there to the somatosensory cortex. This area has been accurately mapped out. Each area of skin has its lot in the cortex. The more receptors active in an area of  skin, the bigger will be its allotment.  With this in mind, scientists outlined the diagram of correlation between the areas of the body and cortex. For example, the hands would have a significantly larger representation, then the back. They constructed a model of  a greatly exaggerated person drawn out on the surface of the brain, a homunculus. 	
	



The scientists are now challenging the theory of brain plasticity. It has been always believed that the brain is plastic during infancy, but after this   critical period of flexible growth, the brain’s nueronal circuitry becomes hardwired. The homunculus was believed to be part of that hardwired system.  Therefore, once a limb is amputated, the allotted area in the cortex should be forever silent. 
	Since the 1960s, neuroscientists have been doing experiments which help us understand what help us understand what is happening in the brain of an amputee who is experiencing the phantom limb pain. Two of the most  prominent  of these experimenters  are Michael Merzenitch  and Timothy Pons.
	In 1980s, Michael Merzenich and his colleagues initiated a study in this field. They worked on a series of experiments which produce curious results. In one such experiment, they amputated a finger of an adult monkey. After a few weeks, they read the signals  of the monkey’s cortex. The expected results was for the hardwired brain ( in the area of the missing finger) to be silent. They were amazed to find that the neurons within the region, fired, each time the adjacent fingers were touched. They explained this by the fact that the remapping was  only a millimeter or two,  not significant amount because that is the approximate length of a neuronal axon. The explanation (one which would not demolish the "hardwired brain theory") was that the existing, unused branches of the axons were ready in contact across the borders of the cortical regions. When normal input from one amputated finger ceased, these dormant connections were invading the vacated region, but only as far as an axon could reach.
In 1991, Timothy Pons experimented on a group of macaques that, in an  unrelated experiment, 12 years earlier, had had the sensory nerves from one arm cut where they entered the spinal cord.  Pons attached electrodes in the cortexes of the monkeys, to investigate what has 12 years of  dormancy had done to the part of the monkeys’ homunculus, where the  limbs have been unplugged. Expecting to find just a few millimeters of encroachment, he was shocked to find the face region had completely invaded the neighboring cortex. In all four animals that were studied, the entire hand and arm region responded when the face was stimulated.
 	Because the numbed limb was not sending any messages  to the cortex, a massive remapping occurred.  Pons explains that in the thalamus, location of the chin and arm lots are next to each other. When the arm stops sending mesages to the  cortex, the chin takes over.









	What is  the  pu
































































	For  more than a hundred years, physicians have published accounts of people who perceive an amputated arm or leg as if it were still there.  Many amputees feel burning, cramping, or shooting pains in these phantom limbs.
Doctors explained this by saying that the patients went through a denial period due to the trauma of loosing a body-part. Experts  have discovered
in the last decade that the sensations which the amputees have been reporting,
is due to a manifestation called Phantom limb phenomena.
	The neurobiologists have been chasing the phantom. Their first attempts were to figure out were do the  sensations originate. When a limb is amputated, the severed nerves that formerly carried messages of touch , temperature, and pain from the skin, form  nodules on their cut ends, called neuromas. For years, the favored explanation was, that the cut nerve endings continue to send impulses up the spinal cord to the brain. This explanation was repealed when  the neurosurgeons cut just above the neuromas. The proof was in the fact that the relief was temporary and therefore that the sensation  must be emanating from the brain. The discovery, that  the sense of touch emanates from our heads rather than our fingertips, leads the researchers onto a new dimension  in neuroscience. 
	It is known to us that  when the receptors of the neurons are stimulated, an electrical impulse is generated. It travels through the spinal cord, to the brain stem. This electrical  impulse travels further to the relay station – thalamus, and from there to the somatosensory cortex. This area has been accurately mapped out. Each area of skin has its lot in the cortex. The more receptors active in an area of  skin, the bigger will be its allotment.  With this in mind, scientists outlined the diagram of correlation between the areas of the body and cortex. For example, the hands would have a significantly larger representation, then the back. They constructed a model of  a greatly exaggerated person drawn out on the surface of the brain, a homunculus. 	
	



The scientists are now challenging the theory of brain plasticity. It has been always believed that the brain is plastic during infancy, but after this   critical period of flexible growth, the brain’s nueronal circuitry becomes hardwired. The homunculus was believed to be part of that hardwired system.  Therefore, once a limb is amputated, the allotted area in the cortex should be forever silent. 
	Since the 1960s, neuroscientists have been doing experiments which help us understand what help us understand what is happening in the brain of an amputee who is experiencing the phantom limb pain. Two of the most  prominent  of these experimenters  are Michael Merzenitch  and Timothy Pons.
	In 1980s, Michael Merzenich and his colleagues initiated a study in this field. They worked on a series of experiments which produce curious results. In one such experiment, they amputated a finger of an adult monkey. After a few weeks, they read the signals  of the monkey’s cortex. The expected results was for the hardwired brain ( in the area of the missing finger) to be silent. They were amazed to find that the neurons within the region, fired, each time the adjacent fingers were touched. They explained this by the fact that the remapping was  only a millimeter or two,  not significant amount because that is the approximate length of a neuronal axon. The explanation (one which would not demolish the "hardwired brain theory") was that the existing, unused branches of the axons were ready in contact across the borders of the cortical regions. When normal input from one amputated finger ceased, these dormant connections were invading the vacated region, but only as far as an axon could reach.
In 1991, Timothy Pons experimented on a group of macaques that, in an  unrelated experiment, 12 years earlier, had had the sensory nerves from one arm cut where they entered the spinal cord.  Pons attached electrodes in the cortexes of the monkeys, to investigate what has 12 years of  dormancy had done to the part of the monkeys’ homunculus, where the  limbs have been unplugged. Expecting to find just a few millimeters of encroachment, he was shocked to find the face region had completely invaded the neighboring cortex. In all four animals that were studied, the entire hand and arm region responded when the face was stimulated.
 	Because the numbed limb was not sending any messages  to the cortex, a massive remapping occurred.  Pons explains that in the thalamus, location of the chin and arm lots are next to each other. When the arm stops sending mesages to the  cortex, the chin takes over.









	What is  the  pu






























































	For  more than a hundred years, physicians have published accounts of people who perceive an amputated arm or leg as if it were still there.  Many amputees feel burning, cramping, or shooting pains in these phantom limbs.
Doctors explained this by saying that the patients went through a denial period due to the trauma of loosing a body-part. Experts  have discovered
in the last decade that the sensations which the amputees have been reporting,
is due to a manifestation called Phantom limb phenomena.
	The neurobiologists have been chasing the phantom. Their first attempts were to figure out were do the  sensations originate. When a limb is amputated, the severed nerves that formerly carried messages of touch , temperature, and pain from the skin, form  nodules on their cut ends, called neuromas. For years, the favored explanation was, that the cut nerve endings continue to send impulses up the spinal cord to the brain. This explanation was repealed when  the neurosurgeons cut just above the neuromas. The proof was in the fact that the relief was temporary and therefore that the sensation  must be emanating from the brain. The discovery, that  the sense of touch emanates from our heads rather than our fingertips, leads the researchers onto a new dimension  in neuroscience. 
	It is known to us that  when the receptors of the neurons are stimulated, an electrical impulse is generated. It travels through the spinal cord, to the brain stem. This electrical  impulse travels further to the relay station – thalamus, and from there to the somatosensory cortex. This area has been accurately mapped out. Each area of skin has its lot in the cortex. The more receptors active in an area of  skin, the bigger will be its allotment.  With this in mind, scientists outlined the diagram of correlation between the areas of the body and cortex. For example, the hands would have a significantly larger representation, then the back. They constructed a model of  a greatly exaggerated person drawn out on the surface of the brain, a homunculus. 	
	



The scientists are now challenging the theory of brain plasticity. It has been always believed that the brain is plastic during infancy, but after this   critical period of flexible growth, the brain’s nueronal circuitry becomes hardwired. The homunculus was believed to be part of that hardwired system.  Therefore, once a limb is amputated, the allotted area in the cortex should be forever silent. 
	Since the 1960s, neuroscientists have been doing experiments which help us understand what help us understand what is happening in the brain of an amputee who is experiencing the phantom limb pain. Two of the most  prominent  of these experimenters  are Michael Merzenitch  and Timothy Pons.
	In 1980s, Michael Merzenich and his colleagues initiated a study in this field. They worked on a series of experiments which produce curious results. In one such experiment, they amputated a finger of an adult monkey. After a few weeks, they read the signals  of the monkey’s cortex. The expected results was for the hardwired brain ( in the area of the missing finger) to be silent. They were amazed to find that the neurons within the region, fired, each time the adjacent fingers were touched. They explained this by the fact that the remapping was  only a millimeter or two,  not significant amount because that is the approximate length of a neuronal axon. The explanation (one which would not demolish the "hardwired brain theory") was that the existing, unused branches of the axons were ready in contact across the borders of the cortical regions. When normal input from one amputated finger ceased, these dormant connections were invading the vacated region, but only as far as an axon could reach.
In 1991, Timothy Pons experimented on a group of macaques that, in an  unrelated experiment, 12 years earlier, had had the sensory nerves from one arm cut where they entered the spinal cord.  Pons attached electrodes in the cortexes of the monkeys, to investigate what has 12 years of  dormancy had done to the part of the monkeys’ homunculus, where the  limbs have been unplugged. Expecting to find just a few millimeters of encroachment, he was shocked to find the face region had completely invaded the neighboring cortex. In all four animals that were studied, the entire hand and arm region responded when the face was stimulated.
 	Because the numbed limb was not sending any messages  to the cortex, a massive remapping occurred.  Pons explains that in the thalamus, location of the chin and arm lots are next to each other. When the arm stops sending mesages to the  cortex, the chin takes over.









	What is  the  pu






























































	For  more than a hundred years, physicians have published accounts of people who perceive an amputated arm or leg as if it were still there.  Many amputees feel burning, cramping, or shooting pains in these phantom limbs.
Doctors explained this by saying that the patients went through a denial period due to the trauma of loosing a body-part. Experts  have discovered
in the last decade that the sensations which the amputees have been reporting,
is due to a manifestation called Phantom limb phenomena.
	The neurobiologists have been chasing the phantom. Their first attempts were to figure out were do the  sensations originate. When a limb is amputated, the severed nerves that formerly carried messages of touch , temperature, and pain from the skin, form  nodules on their cut ends, called neuromas. For years, the favored explanation was, that the cut nerve endings continue to send impulses up the spinal cord to the brain. This explanation was repealed when  the neurosurgeons cut just above the neuromas. The proof was in the fact that the relief was temporary and therefore that the sensation  must be emanating from the brain. The discovery, that  the sense of touch emanates from our heads rather than our fingertips, leads the researchers onto a new dimension  in neuroscience. 
	It is known to us that  when the receptors of the neurons are stimulated, an electrical impulse is generated. It travels through the spinal cord, to the brain stem. This electrical  impulse travels further to the relay station – thalamus, and from there to the somatosensory cortex. This area has been accurately mapped out. Each area of skin has its lot in the cortex. The more receptors active in an area of  skin, the bigger will be its allotment.  With this in mind, scientists outlined the diagram of correlation between the areas of the body and cortex. For example, the hands would have a significantly larger representation, then the back. They constructed a model of  a greatly exaggerated person drawn out on the surface of the brain, a homunculus. 	
	



The scientists are now challenging the theory of brain plasticity. It has been always believed that the brain is plastic during infancy, but after this   critical period of flexible growth, the brain’s nueronal circuitry becomes hardwired. The homunculus was believed to be part of that hardwired system.  Therefore, once a limb is amputated, the allotted area in the cortex should be forever silent. 
	Since the 1960s, neuroscientists have been doing experiments which help us understand what help us understand what is happening in the brain of an amputee who is experiencing the phantom limb pain. Two of the most  prominent  of these experimenters  are Michael Merzenitch  and Timothy Pons.
	In 1980s, Michael Merzenich and his colleagues initiated a study in this field. They worked on a series of experiments which produce curious results. In one such experiment, they amputated a finger of an adult monkey. After a few weeks, they read the signals  of the monkey’s cortex. The expected results was for the hardwired brain ( in the area of the missing finger) to be silent. They were amazed to find that the neurons within the region, fired, each time the adjacent fingers were touched. They explained this by the fact that the remapping was  only a millimeter or two,  not significant amount because that is the approximate length of a neuronal axon. The explanation (one which would not demolish the "hardwired brain theory") was that the existing, unused branches of the axons were ready in contact across the borders of the cortical regions. When normal input from one amputated finger ceased, these dormant connections were invading the vacated region, but only as far as an axon could reach.
In 1991, Timothy Pons experimented on a group of macaques that, in an  unrelated experiment, 12 years earlier, had had the sensory nerves from one arm cut where they entered the spinal cord.  Pons attached electrodes in the cortexes of the monkeys, to investigate what has 12 years of  dormancy had done to the part of the monkeys’ homunculus, where the  limbs have been unplugged. Expecting to find just a few millimeters of encroachment, he was shocked to find the face region had completely invaded the neighboring cortex. In all four animals that were studied, the entire hand and arm region responded when the face was stimulated.
 	Because the numbed limb was not sending any messages  to the cortex, a massive remapping occurred.  Pons explains that in the thalamus, location of the chin and arm lots are next to each other. When the arm stops sending mesages to the  cortex, the chin takes over.









	What is  the  pu






























































	For  more than a hundred years, physicians have published accounts of people who perceive an amputated arm or leg as if it were still there.  Many amputees feel burning, cramping, or shooting pains in these phantom limbs.
Doctors explained this by saying that the patients went through a denial period due to the trauma of loosing a body-part. Experts  have discovered
in the last decade that the sensations which the amputees have been reporting,
is due to a manifestation called Phantom limb phenomena.
	The neurobiologists have been chasing the phantom. Their first attempts were to figure out were do the  sensations originate. When a limb is amputated, the severed nerves that formerly carried messages of touch , temperature, and pain from the skin, form  nodules on their cut ends, called neuromas. For years, the favored explanation was, that the cut nerve endings continue to send impulses up the spinal cord to the brain. This explanation was repealed when  the neurosurgeons cut just above the neuromas. The proof was in the fact that the relief was temporary and therefore that the sensation  must be emanating from the brain. The discovery, that  the sense of touch emanates from our heads rather than our fingertips, leads the researchers onto a new dimension  in neuroscience. 
	It is known to us that  when the receptors of the neurons are stimulated, an electrical impulse is generated. It travels through the spinal cord, to the brain stem. This electrical  impulse travels further to the relay station – thalamus, and from there to the somatosensory cortex. This area has been accurately mapped out. Each area of skin has its lot in the cortex. The more receptors active in an area of  skin, the bigger will be its allotment.  With this in mind, scientists outlined the diagram of correlation between the areas of the body and cortex. For example, the hands would have a significantly larger representation, then the back. They constructed a model of  a greatly exaggerated person drawn out on the surface of the brain, a homunculus. 	
	



The scientists are now challenging the theory of brain plasticity. It has been always believed that the brain is plastic during infancy, but after this   critical period of flexible growth, the brain’s nueronal circuitry becomes hardwired. The homunculus was believed to be part of that hardwired system.  Therefore, once a limb is amputated, the allotted area in the cortex should be forever silent. 
	Since the 1960s, neuroscientists have been doing experiments which help us understand what help us understand what is happening in the brain of an amputee who is experiencing the phantom limb pain. Two of the most  prominent  of these experimenters  are Michael Merzenitch  and Timothy Pons.
	In 1980s, Michael Merzenich and his colleagues initiated a study in this field. They worked on a series of experiments which produce curious results. In one such experiment, they amputated a finger of an adult monkey. After a few weeks, they read the signals  of the monkey’s cortex. The expected results was for the hardwired brain ( in the area of the missing finger) to be silent. They were amazed to find that the neurons within the region, fired, each time the adjacent fingers were touched. They explained this by the fact that the remapping was  only a millimeter or two,  not significant amount because that is the approximate length of a neuronal axon. The explanation (one which would not demolish the "hardwired brain theory") was that the existing, unused branches of the axons were ready in contact across the borders of the cortical regions. When normal input from one amputated finger ceased, these dormant connections were invading the vacated region, but only as far as an axon could reach.
In 1991, Timothy Pons experimented on a group of macaques that, in an  unrelated experiment, 12 years earlier, had had the sensory nerves from one arm cut where they entered the spinal cord.  Pons attached electrodes in the cortexes of the monkeys, to investigate what has 12 years of  dormancy had done to the part of the monkeys’ homunculus, where the  limbs have been unplugged. Expecting to find just a few millimeters of encroachment, he was shocked to find the face region had completely invaded the neighboring cortex. In all four animals that were studied, the entire hand and arm region responded when the face was stimulated.
 	Because the numbed limb was not sending any messages  to the cortex, a massive remapping occurred.  Pons explains that in the thalamus, location of the chin and arm lots are next to each other. When the arm stops sending mesages to the  cortex, the chin takes over.









	What is  the  pu






























































	For  more than a hundred years, physicians have published accounts of people who perceive an amputated arm or leg as if it were still there.  Many amputees feel burning, cramping, or shooting pains in these phantom limbs.
Doctors explained this by saying that the patients went through a denial period due to the trauma of loosing a body-part. Experts  have discovered
in the last decade that the sensations which the amputees have been reporting,
is due to a manifestation called Phantom limb phenomena.
	The neurobiologists have been chasing the phantom. Their first attempts were to figure out were do the  sensations originate. When a limb is amputated, the severed nerves that formerly carried messages of touch , temperature, and pain from the skin, form  nodules on their cut ends, called neuromas. For years, the favored explanation was, that the cut nerve endings continue to send impulses up the spinal cord to the 


 
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