Those in neuroscience have most likely heard of the neuroscientist V.S. Ramachandran and his work in studying abnormalities observed between the mind body relationship. He has inspired many, including me to have a deep curiosity about the world through the lens of neuroscience. In his book “Phantoms in the Brain”, he describes the phenomenon of phantom limp pain (PLP) and phantom limb sensation (PLS) in amputees. These experienced symptoms are associated with how the somatosensory cortex represents the entire body. This cortical mapping and the brains’ ability for neuroplasticity or cortical reorganization is one mechanism that explains why amputees still have the experience of the limb that is no longer present. To continue Ramachandran’s work 1998, I would like to briefly show where we are at with understanding PLP/PLS and what is being done to alleviate its symptoms. In spirit of Ramachandran, I would like to keep in mind the deeper implications of how we relate to our bodies, what is us and other, and what does it mean to be embodied beings.
PLP has a tremendous
impact on quality of life in amputees. The number of amputees each year is
increasing and not just due to traumatic car accidents but also due to the
increase in diabetes and tumors. Many techniques used to alleviate PLP/PLS have
evolved since the classical mirror therapy developed my Ramachandran. Since
then, Transcranial Magnetic Stimulation (TMS) has been used over the cortical
maps to activate the areas representing the absent limb. Acupuncture, drug
treatments, and spinal cord stimulation are other therapies but none of them
alone have had consistent success in dealing with PLP/PLS.
During a neuroscience
seminar, I had the honor to listen to Dr. Dumanian’s talk on the incredible work
he is doing with using Target Muscle Reinnervation (TMR) to alleviate PLP. His
work seems very promising compared to the other therapies offered. What
previous procedures had done was just innervated the amputated sense nerves
into the nearby muscle flesh. Dr. Dumanian’s approach was to innervate the sense
nerve with a nearby motor nerve that wouldn’t critically impact other motor
functions. The reasoning behind is ingenious. Instead of having an open loop motor-sensory
system with the nerve just embedded in the muscle, innervating the sense and
motor nerve together creates the closed loop system. As Dr. Dumanian states, giving
the sense nerve “something to do” could reduce the effects of cortical reorganization.
Over the course of the year, patients reported PLP had reduced compared to the
standard procedure.
TMR research focuses
on what new treatments might look like in the future, but we are only looking
at the peripheral nerve system. What have we learned in the CNS with cortical
reorganization? What Ramachandran hypothesized was that neurons in the brain
are always in competition with each other. If part of the somatosensory cortex is
inactive due to an amputated limb, these areas don’t atrophy but get taken over
by surrounding areas. A study that caught my attention was looking beyond the
somatosensory cortex in how other areas are becoming reorganized. Particularly
the right parietal cortex. The work done by Bao et al. 2021 in their study “Parietal
Lobe Reorganization and Widespread Functional Connectivity Integration in
Upper-Limb Amputees: A rs-fMRI Study”, looked at how areas in the right parietal
cortex might become reorganized.
Amputees that have
had upper-limb amputations have also been shown to have body image disorders.
DSM-V describes this condition as having an intense anxiety due to the sense
that their image of their body does not match reality. The right parietal
cortex is a region of interest (ROI) since patients with lesions to this area
have various body disorders. Using resting state fMRI (rs-fMRI), a technique
used to measure brain activity but not needing to perform a task, the
researchers have identified two indicators in the right parietal cortex that
were significantly different from a healthy control group. They showed that there
was a positive correlation with these indicators and self-reports of PLS. What
these indicators show is that this is a decrease connectivity between various
brain regions. The limitation to this study is that it is only post operative
and that there needs to be a longitudinal study to see how these areas continually
reorganize.
This study is a
started point in understanding the brain and the body as a whole. Future research
is needed not only for understanding the mechanisms behind reorganization, but
for better therapies for amputees. The questions that still arises for me is
how does the body (particularly the nervous system) maintain itself as a dynamical
self-organizing system? In Dr. Dumanian’s work, he demonstrates that closed-loop
systems are critical. In Bao’s et al. work, they showed that areas of the parietal
cortex might serve as hubs to how we maintain our sense of embodiment. It is
exciting to see where research has gone since Ramachandran and how more areas
of research are converging on better understanding the complexities of life.
References:
Bao, Wei, H., Luo, P., Zhu, H., Hu, W., Sun,
Y., Shen, J., Zhu, T., Lin, J., Huang, T., Li, J., Wang, Z., Li, Y., &
Zheng, X. (2021). Parietal Lobe Reorganization and Widespread Functional
Connectivity Integration in Upper-Limb Amputees: A rs-fMRI Study. Frontiers
in Neuroscience, 15, 704079–704079. https://doi.org/10.3389/fnins.2021.704079
Dumanian, Potter, B. K., Mioton, L. M., Ko, J.
H., Cheesborough, J. E., Souza, J. M., Ertl, W. J., Tintle, S. M., Nanos, G.
P., Valerio, I. L., Kuiken, T. A., Apkarian, A. V., Porter, K., & Jordan,
S. W. (2019). Targeted Muscle Reinnervation Treats Neuroma and Phantom Pain in
Major Limb Amputees: A Randomized Clinical Trial. Annals of Surgery, 270(2), 238–246. https://doi.org/10.1097/SLA.0000000000003088
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