We already know that the human brain is indispensable to build a shining civilization or to survive long enough to teach our accumulated information through generations to the next one like inventions and knowledge, changing the perception of the nature and the nurture once and for all, as well as imagination. However, we focus on the question how this imagination creates a pain perpetuated by an organ that is not there anymore, mostly known as the phantom pain.
What is the phantom pain? It is actually a very tricky question to answer due to the fact that it does not include only one part of the brain or one operational system; it is more like a collaboration of the brain and the nervous system simultaneously. Basically, when an organ is absent or not working properly because of amputation or a stroke – an amputated hand perfectly exemplifies this situation, the brain is starting to realize the absence of amputated organs eventually and prunes the pathways and neural connections allocated to the hand. That is the usual and expected scenario most of the time but, in the phantom pain cases, it might not be the way to interpret the hand for brain. In other words, brain keeps the pathways and connections alive in both ways even though there are no receiver neurons giving a feedback to the signals yielded by brain itself; when brain cannot manage to elicit a response from the amputated hand, it interprets the unanswered signal as the amputated hand emanates pain. To better comprehend how the phantom pain occurs, I quoted an explanation from Ramachandran(the director of the Center for Brain and Cognition) down below.
"…When your arm is intact, the sensory feedback from the skin, muscles and joint sensors in your arm, as well as the visual from your eyes, are all testifying in unison that your arm is not in fact moving. Even though your motor cortex is sending move signals to your parietal lobe, the countervailing testimony of the sensory feedback acts as a powerful veto. As a result, you don’t experience the imagined movement as though it were real. If the arm is gone, however your muscles, skin, joints, and eyes cannot provide this potent reality check. Without the feedback veto, the strongest signal entering your parietal lobe is the motor command to the hand. As a result, you experience actual movement sensations." (1)
Then how could mirrors help the phantom pain to heal or gone permanently? As the aforementioned explanation emphasize, the phantom pain is caused by the misinterpretation of the feedback due to the missing potential check of not functioning organs, and entrenched motor-command signals. In other words, there is no control mechanism to intercept the signal transferring, halting the occurred pain permanently. But what happens if you place a mirror between the amputated hand and the intact hand a mirror, settled at an angle to see the movements as though the amputated hand performs; this simple explanation is astonishingly the answer we are looking for, through this article. The reason is as follows. Brain has a capability to adapt any situation or information which is albeit completely new and unknown if there is enough time to inspect and internalize throughout. It is called brain plasticity. In other words, brain can either create or prune the pathways to learn or, in this case, unlearn something. And, the perception of the mirror hand provides the feedback by proving that the motor signal and the response are not the same as expected so there must be no hand at all. Surprisingly, brain itself adapts this new situation, and alleviates the phantom pain by merely seeing a replica of the actual hand (a mirror hand of the existing hand). This new feedback type instigating some discrepancy between the visual perception and the phantom hand is called the mirror visual feedback or MVF. In that case, the brain relearns a pathway to create it again in a different way via MVF. As Ramachandran said below;
"…No one has proven the mechanism yet, but here is how I suspect it works. When faced with such a welter of conflicting sensory inputs – no joint or muscle feedback, impotent copies of motor-command signals, and now discrepant visual feedback thrown in via the mirror box – the brain just gives up and says, in effect, “To hell with it; there is no arm.” The brain resorts to denial." (2)
(1) Ramachandran, V. S. "Phantom Limbs and Plastic Brains." The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human. New York: W.W. NORTON & COMPANY, 2012. 31. Print.
(2) Ramachandran, V. S. "Phantom Limbs and Plastic Brains." The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human. New York: W.W. NORTON & COMPANY, 2012. 34. Print.
Figure - 30.1 https://newatlas.com/brain-plasticity-age-related-cognitive-decline-prozac/55979/
Figure - 30.2 https://www.ivketamine.com/phantom-limb/
Figure - 30.3 https://www.bbc.com/news/magazine-15938103
Figure - 30.4 https://www.clinicalpainadvisor.com/neuropathic-pain/visual-feedback-effective-option-for-phantom-limb-pain/article/395039/