Corporeal Awareness: "You don't need the body to feel the body"

"You don't need the body to feel the body"

Biology 202

Web Paper 1

'The Brain is wider than the Sky

For put them side by side

The other will contain

With ease and You beside

--Emily Dickinson, "The Brain is wider than the Sky"

According to Emily Dickinson, the entity that is the brain is infinite in its capacity and ability. A perplexing irony rests in the notion that the brain—a deceptively small and seemingly finite body of matter—could encompass all things that we mere mortals view to be vast and unending; that the brain can construct “reality” and furthermore, that it may in its own right be a construction of itself is truly mind-boggling. While in the past I have favored Descartes’ “mind-body dualism” theory of behavior, I have encountered a set of observations that compel me to critically contemplate Dickinson’s “it’s all in the brain” philosophy. In light of our ongoing debate regarding the validity of both schools of thought, I endeavor to highlight some observations regarding the notion of bodily awareness and its relation to the brain in hopes that it will facilitate our unending journey to “getting it less wrong.”

The phenomenon known as “phantom pain” occurs in roughly 50-80% of amputees (1) and is defined as pain in a non-existing body structure. Cases of phantom pain and, more generally, phantom awareness have been documented with remarkable detail, particularly during war periods. Christian Bagge’s story, like countless others who went to Iraq, illustrates what it is like to live with phantom pains:"[the pain] came on suddenly and felt like someone was smashing my toes with a hammer (2),” explained the National Guard soldier, when asked to describe the discomfort he was experiencing in his “feet.” “On a scale of one to ten, I'd say it was a six or a seven, but then again, my 'ten' is getting both of my legs blown off.” Oddly enough, both of the Christian’s legs were amputated after the soldier was hit by two bombs in Iraq; by the time he returned home, both of his legs had long been surgically removed but the excruciating crushing sensation continued, creating a vivid perception of the missing body part.

The sum of Christian’s experiences, as well as those of several other amputees, reveal a host of interesting qualities about “phantom” body parts. They are often perceived immediately after limb loss by most amputees (1), however for some, they may emerge years and even decades after limb loss. In some instances, the phantom may take on a posture that is abnormal, distorted or disfigured. Typically, amputees report that they can move their phantom limb through normal ranges; a small percentage of subjects report phantom limb movement through anatomically impossible ranges. (3) Additionally, phantom sensations are manifested in several forms, often depending on the state of the limb prior to amputation; sensations run the gamut of benign pressure, cramping, burning, itching, pinching, stabbing, stinging, aching, crushing, twisting, and grinding (3). There exist several cases in which subjects perceive their phantoms to be completely paralyzed, or under volitional control. Lastly, it is also worth noting that phantom sensations are not limited to limbs; they are known to manifest in a variety of situations in which any given bodily structure is removed. For example, breast removal, eye removal, and tooth extractions are all commonly known to yield phantom pains (1).

While the etiology of such “phantoms” remains nebulous, Freudian theories, implicating subconscious grievances over the loss of said limb, have long dominated the scene. Interestingly, this theory does not account for all phantom cases—specifically, the 20% of congenitally limb-deficient individuals who experience phantom sensations (4). For instance, K. Poeck’s 1964 case study described an 11-year-old girl born without both of her arms. Remarkably, the subject learned to solve simple arithmetic problem by counting on her phantom fingers (4). Similarly, V. Ramachandran reported similar phenomena in his 1993 study; his report described a 20-year-old female who displayed congenital limb deficiency, yet experienced very vivid phantom limbs that often gesticulated during conversation. The sum of this and all aforementioned observations raise an intriguing question: how can the nervous system maintain sensory input mechanisms in regions that are not physically a part of the organism? While memories of the limb immediately prior to amputation may endure in the phantom, this is still unable to explain why individuals who never experienced life with limbs are able to experience phantom sensations. Ongoing investigations surrounding the aforementioned query promise to yield illuminating insight regarding the functioning of the brain in the generation of body schemas, our notion of “body space”—or “corporeal awareness”— and nervous system plasticity.

New insights regarding the neuropathology of phantom pain have come from studies demonstrating changes in the structural architecture of the primary somatosensory cortex (also known as the homunculus) which is essentially a neural map of the body’s surface area (5). In order to investigate this possibility, Ramachandran et. al. amputated digits in adult owl monkeys and studied the reorganization of the somatosensory cortex. They found that regions in the cortex that were previously associated with the amputated fingers were invaded, and later dominated, by adjacent areas in the homunculus model (7). The research team then postulated that post-amputation there is a reorganization of the cortex that leads to altered body image perception (7).

These findings were supported by several other clinical studies; one in particular revealed that touching the cheek in patients with amputated arms often induced phantom limb pains. In some cases, specific parts of the phantom arm —elbow, thumb, index finger etc–would respond to varying the type of “touch” (6). This piece of information is of extreme interest to us because in the normal homunculus representation of the body, the cheek is close to the arm. These studies revealed that, in response to arm amputation, the representation of the face will extend and cover the previous arm representation. Thus, contrary to popular belief, these observations point to the seeming plasticity of the somatosensory cortical structure.

Enlightening as this may be, again no information is presented with regards to individuals with congenital limb deficiencies. In an attempt to fill the void, R. Melzack postulates that there may exist a hard-wired mechanism in the brain that connect specific groups of neurons in the cortical structures and thus, could possibly account for the appearance phantom limb pain (7). He states “the brain does indeed carry a map of the body. But the map is innate and genetic, independent of our life experience…the body we perceive is in large part built into our brain -- it's not entirely learned. In fact, you do not need the body to feel the body." If Melzack is “less wrong,” then even our sense of “body-ness” is but a construction of the brain. What, then, is real? What does this say about the construction of "reality” and human agency? If everything is indeed in the brain how do we account for the fact that 80% of individuals with congenital limb deficiencies who don’t experience phantom pains and the vast amount of variation between subject experiences? Shouldn’t it follow that similar situations might yield similar outcomes? Like all good questions, these may forever remain unanswered.

References

1. http://en.wikipedia.org/wiki/Phantom_limb

2. Christian Bagge’s story

3. Properties of phantom limbs

4. Central mechanisms in phantom limb perception: The past, present and future

5. Cortical homunculus

6. Phantom limb pain: a case of maladaptive CNS plasticity?

7. Phantom pain and possible lessons for consciousness

8. The effect of tactile and visual sensory inputs on phantom limb awareness