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Lost Limbs: Why Amputees Can Still Feel Their Hands and Feet?
When many people hear the word "amputation," they immediately think of a lost limb and the challenges that come with it. However, amputees often report that they can still feel their lost limbs, a phenomenon known as the "phantom limb phenomenon." Researchers have delved into this phenomenon and are trying to understand how amputees retain an intact model of their bodies in their minds.
Body Schema is an organism’s internal model of its own body, including the position of its limbs. This concept was first proposed by neuroscientist Henry Hyde and allows us to explore this phenomenon more clearly.
Body schema is different from body image, which involves people's perceptions, attitudes, and beliefs about their bodies. Body schemas are the sensorimotor abilities that control movement and posture. It can be seen that amputees can still feel their lost limbs because the body schema in the brain still retains the existence of those limbs.
The operation of body schema
This concept can be traced back to the research of Henry Hyde and Gordon Morgan Holmes in the early 20th century. At that time, they observed dysregulation of spatial representation in patients with damage to certain areas of the brain. Over time, the concept evolved, and body schemas were shown to encompass a variety of functions, such as motion tracking and perception of external objects.
According to research by neuroscientists Patrick Haggard and Daniel Volpert, body schemas have certain spatial encoding capabilities and can integrate information based on multiple sources such as touch and vision.
Phantom limb phenomenon: strange reactions of the brain
Amputees often experience phantom limbs, a phenomenon based on body schemas. Even if a limb is lost, the brain appears to respond to sensations in that part. In studies, 90–98% of amputees report feeling their lost limb, and in some cases, these phantom limbs may even experience pain, which is known as “phantom limb pain.” This phenomenon highlights the flexibility of the body schema and challenges our perception of physical existence.
The occurrence of the phantom limb phenomenon can be explained by the misalignment of sensory neurons in the brain. These neurons may reorganize and connect to adjacent cortical areas, causing amputees to still feel the "non-existent" limb.
Update and adaptability of body schema
The body schema is not static; it is constantly updated as the individual grows and the environment changes. As people learn to use tools or perform new movements, body schemas adapt. For example, when a person habitually uses a new tool, the tool is also integrated into the body's schema by the brain. This is especially true for unfamiliar hand movements. Research shows that the human nervous system exhibits extremely high plasticity and can even quickly integrate input external objects.
Through experiments with the "rubber hand illusion", scientists have proven that body schemas can be reorganized in a few seconds, showing the randomness and flexibility of body schemas.
The use of body schemas and tools
In addition to self-perception, body schemas are also closely related to tool use. As the individual practices, the tool becomes incorporated into the body schema, which is not only the result of spinal reflexes but also involves higher level cognitive processes. Whether using simple everyday tools or performing complex manual operations, body schema plays a key role in these processes.
Interestingly, neuroscience research has even shown that the neural responses to tool use are similar to those of the hands, suggesting that the brain still treats the tool as part of its own body when using it. This further strengthens the theory that the body schema may extend beyond the physical body and include external objects within its scope.
Exploration and future directions of phantom limb phenomenon
By studying the phenomenon of phantom limbs, we can not only gain a deeper understanding of body schemas, but also explore how the nervous system responds to the absence of the body. In future research, this may help us design more effective rehabilitation programs to help amputees better rebuild their awareness and control of their bodies.
These studies not only impact clinical practice, but also challenge our understanding of the binding between consciousness, self, and body, reminding us to think about what truly constitutes the concept of "body."
As we gain a deeper understanding of body schemas and related phenomena, the question naturally arises: If the brain can still "perceive" limbs after losing them, what is the true definition of the body?
