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Transcript of Phantom Limbs
Phantoms in the Brain
Ch. 2: Knowing Where to Scratch
Ch. 3: Chasing the Phantom
At age 17, Tom Sorenson lost his arm in a car accident...
but he could still wiggle each "finger," "reach out" and "grab" objects, "pat" his little brother on the back...
"Phantom limb": term coined by Dr. Silas Weir Mitchell after the civil war.
women with phantom breasts after mastectomies
patient with a phantom appendix
patient who experienced phantom erections after his penis was amputated
Some important questions:
are these maps determined by genes and present at birth?
Even if the maps are present at birth, can they be changed by experience?
when Dr. Ramachandran swabbed his cheek with a Q-tip, Tom felt it on his cheek AND ON HIS MISSING THUMB...
Timothy “Tim” Philip Pons, 49, Professor of Neurosurgery at Wake Forest University School of Medicine, died 19 January 2005, after a long and courageous battle with liver disease. He was a neuroscientist of the first rank.
Tim got his first taste of neuroscience at the University of North Carolina at Greensboro, working with Walter Salinger on adult neural plasticity in the lateral geniculate nucleus, and he met Preston Garraghty, a life-long friend, colleague, and collaborator. Tim went on to do a Ph.D. with Jon Kaas at Vanderbilt University. This work led to extensive publications on area 2 of macaque parietal cortex, and revealed a basis for the sensory plasticity after adult nerve injury previously discovered by Michael Merzenich and others in Kaas's lab.
In 1984, Tim moved to Mortimer Mishkin's laboratory at the N.I.M.H., where he undertook to determine whether the primate somatosensory system shared organizational features with the hierarchically-organized parallel processing streams in the visual system. Tim showed that the second somatosensory area (S-II) of macaques required inputs from primary (S-I) cortex for its activation. This result contrasted with what had been demonstrated in non-simian species, and still stands as a reminder that mice are men only some of the time. His subsequent experiments, conducted after a period of recovery from S-I ablation, revealed that the formerly-deactivated region of S-II had regained responsiveness, but to skin surfaces whose S-I representations remained intact. This finding served as a precursor for experiments that would become the defining nexus of Tim's professional career.
Phantom Limb Phenomenon
what's going on??
hyperactivity of severed nerves?
Wilder Penfield at work
When Dr. R. touched Tom's upper lip, Tom also felt a touch on his index finger.
And when his lower jaw was touched, he felt it on his missing pinkie.
and then Dr. R. found a SECOND map of Tom's hand.
this map was on his upper arm just a few inches above the line of amputation
how would the rewiring occur?
sprouting of new connections?
or activation of connections already in place?
A graduate student who lost her left leg below the knee in an accident on her uncle's farm came to see Dr. R.
An engineer who lost his leg below the knee had a similar problem.
orgasms in their feet
About 70% of people experience PAIN in their phantom
born without arms
phantoms since childhood
"they're 6-8 inches too short"
they gesticulate, but don't swing when she walks
Is our neural circuitry for body image hard wired?
-determined by genes, not dependent on motor & tactile experience
about 1/3 of phantom limb patients can't move their phantoms. How can a nonexistent limb be paralyzed??
term coined by English neurologists, Lord Russell Brain and Henry Head
refers to one's internal image and memory of one's body in space and time
depends on parietal lobes
combining information from multiple sources (kinesthesis, eyes, motor commands, etc.)
complex motor behaviors:
A. supplemental motor area sends out 3 signals:
1. to motor cortex (signals to muscles)
2. to cerebellum
3. to parietal lobes (info about intended movement)
B. feedback loop, from kinesthetic receptors to brain
allows brain to compare intention to actual performance
treatment for paralyzed phantom?