For thousands of years, humanity has been consumed with questions about the world around them. Many of these questions have plagued humanity with an undying thirst of curiosity; a curiosity which has driven men and women to explore the ends of the globe. And now, we continue our journey as we gaze upon the stars and the infinite depths of space. But as we continue to explore the cosmos in search for answers, another journey still remains; a journey into territory so mystifying, stupefying, and full of complexity. What remains is the greatest journey of them all: the journey into the mind and the inner self.
It has been the task of philosophy and religion for many years. The western world in particular, has been dominated by a dichotomous definition of the self for centuries; a duality of both body and soul. The mind and body are presumed separate, consisting of different but interacting substrates. And when the self sheds its "mortal coil," it begins an ethereal and mystical adventure into the afterlife.
Rene Descartes, in an attempt to ward off the throes of skepticism on its own turf, began an ultimate quest of doubt and certainty. In a series of essays entitled Meditations, Descartes inferred that he could doubt everything except his own self-existence, and consequently coined the maxim, "Cogito, Ergo Sum." Latin for, "I think, therefore I am." Of course, the sense of self existence is so immediate, so intuitive, how can anyone deny that they exist? Anyone who does so must be absurd. However, it turns out that this sense of self-existence may be illusory, a sort of post-hoc realization. Accordingly, the Dharmic ideology of the self, that the self is a temporary illusion, may not be so far-fetched.
What lies in our immediate path is a new revolution of ideas and theories; a new paradigm shift as neuroscience continues to unlock the secrets of the mind and the nature of self. Just as the Copernican revolution changed our understanding of the cosmos (that the earth is not the center of the universe) so too, will science change our understanding of what gives rise to the self.
From a neuroscientific perspective, there are many aspects of the self. According to neuroscientist Vilayanur S. Ramachandran of the University of California, one of the defining characteristics of the self is the sense of embodiment and ownership of a body. Although we do in fact have a physical body, the brain is responsible for constructing a body-image: an internal sense that we operate and possess a body.
Our Sixth Sense
Central to the brain, is its vast network of neurons. With input from sensory organs, this ocean of neural connectivity constructs the sensuous world that we each experience. Our neurons fire to represent every aspect of reality; such as the vibrant afterglow of a sunset, familiar faces, our favorite songs, the smell of freshly-ground coffee, the mouthwatering taste of spaghetti, and even the position of one's body as they read. This spectrum of sensory experience is entirely constructed in our brains. For example, if you were to hold a rose, the neurons which correspond to the many aspects of the rose (i.e. color, texture, smell, and orientation) would fire, allowing you to experience it in your mind.
Consider the visual system in the brain. We have the eyes, the optic nerves, the lateral geniculate nucleus in the thalamus, and the visual cortex. Vision is a process, one that involves a stimulus (in this case light) and a physiological reaction in the brain. When light reaches the eyes, it is focused onto the retina. The retina is comprised of tiny light-sensitive receptors (rods and cones) that make up your entire field of vision. When these rod and cone receptors are stimulated by light, electrical nerve impulses are triggered. These impulses travel down the optic nerve, sending information to the lateral geniculate nucleus in its wake. The lateral geniculate nucleus regulates and organizes the incoming sensory information, then relays it to the visual cortex. Our entire field of vision is mapped out onto the visual cortex. With sensory input from the eyes, the neurons in the visual cortex fire to represent everything we see.
Despite what many of us have been told, we have more than five senses. There is a sixth sense that we take for granted. We constantly rely on this sixth sense to perform every physical activity; from turning the pages of a book, to tossing a football in midair. However, it is a sense that hides in the depths of our subconscious. In fact is it so autonomous, so well blended within the shadows of our daily lives that we do not realize it is there. It is the sense that we have a body, which involves vision, the vestibular system, and most of all proprioception; the sense of position, muscle contraction, weight distribution, and movement (as discovered in the late nineteenth century, by scientist Charles S. Sherrington).
Like our retinas that allow us to see, there are tiny receptors within our skin, organs, muscles, joints, and tendons. The receptors within our muscles, joints, and tendons are called proprioceptors. These receptors are stimulated when we bend, sit, run, walk, throw, talk, and so on. As we perform such activities with our bodies, nerve impulses travel into the spinal chord and the brain, exciting neurons in the thalamus, somatosensory cortex, and parietal lobes. Just as there is map of the visual field on the visual cortex, there are dynamic body maps which are involved in the representation of the human body. Most notable is the primary somatosensory receiving area (S1) of the somatosensory cortex, where the sensory homunculus or "little man" resides. The human body is oddly distributed onto this cortical strip; the head, genitalia, and internal organs are dislocated from the rest of the body. Nonetheless, the neurons in this region are responsible for cutaneous (skin), visceral (organ), and proprioceptive sensation, as they fire to represent each part of the human body, and therefore take part in the construction of the body-image. Ablation to any of these areas may result in a number of things; from a loss of proprioception to disturbances of the body-image.
Imagine what would happen if your brain was ravaged by a malignant tumor. You might go blind, and this blindness could be caused by a number of reasons. If the tumor was to damage any areas of the visual system, it would result in some form of blindness. For example, damage to the visual cortex alone would result in blind sight: an unusual phenomenon where one is blind, but able to visually detect moving objects, as other visual cortices (i.e. the parietal lobes) remain intact. Now shift this hypothetical tumor towards the cortices involved with proprioception. It would be analogical to damaging the visual cortex, resulting in blindness. However in this sense, it would result in the discontinued sense of having a body.
A Soul in the Brain
In cases of anosognosia, parts of the body are disassociated from the rest of the body-image. Anosognosia is a disorder commonly found in left-side hemiplegics, who are paralyzed on the left side of the body. Most anosognosiacs are not aware of their left-side paralysis, and some may not even recognize left-side paralysis in other people. When asked by doctors to raise a paralyzed arm, they will either do nothing, or raise their right arm. A common group of symptoms may include neglect towards the affected side of their body. They may dress, groom, and apply makeup only to the side that is intact. This kind of anosognosia normally involves a stroke on the right side of the brain, which damages somatic and parietal cortices among other things. It should be noted that the left side of the body is represented by the right side of the brain, and the right side of the body is represented by the left side of the brain. Also there is hemisphere specialization; only one side of the brain may dominate in a particular function, despite there being two hemispheres of the brain. Just as language and mathematics are dominated by the left hemisphere, art, emotion, and even integrated body sense are dominated by the right hemisphere. Since the right somatic and parietal cortices are damaged in such anosognosiacs, one can assume that their sense of body integration has slightly disintegrated.
Sometimes anosognosiacs suffering from left-side paralysis in particular limbs will experience a disassociation with those limbs. For example, patients with a paralyzed leg may be convinced that it is not part of their own body (perhaps the severed leg of another person.) They will assert that their real leg has disappeared, and in this conclusion, attempt to shove or kick their own leg out of bed. Since it is their own limb, seamlessly connected to the rest of their body, they manage to fall out of bed with it.
In Oliver Sacks' book, The Man Who Mistook His Wife for a Hat, he describes a patient named Christina, who suffered from a selective neuritis. Following a wrongful diagnosis by a psychiatrist, Dr. Sacks discovered an infection in her spinal fluid, which had destroyed sensory nerves and disconnected her entire body from the somatosensory and parietal cortices in her brain. She experienced a complete loss of proprioception, a total sense of disembodiment. Although she had a physical body, she had no internal image of a body, no body-image. Christina would flail and overshoot her limbs. Her mouth was slack-jawed, and her voice flat. Her entire body would flop around like a rag doll. Standing or sitting straight was nearly impossible for her. Of course the sense of disembodiment is hard to imagine. It is best explained in her own words: "I may lose' my arms. I think they're one place, and I find they're another. This 'proprioception' is like the eyes of the body, the way the body sees itself. And if it goes, as it's gone with me, it's like the body's blind."
Conversely is the phenomenon of phantom limb syndrome. Many amputees, who have lost parts of their own body, continue to feel the presence of them (as the body-image remains mostly intact.) Often, the presence of these phantoms are so convincing that patients may attempt step out of bed with missing legs or feet, or try to pick up cups with a missing hand. Even people who are born without arms or legs can sense the presence of their missing limbs. Accordingly, many of these phantoms move with the rest of the body. A phantom hand can wave goodbye. A phantom leg can bend as one sits. Imagine a little girl, born without arms, doing arithmetic by counting fingers that aren't really there (Ronald Melzack, 1997-2006.)
Phantoms are integral to wearing prosthetics. They fit prosthetics like a glove. No amputee can effectively use a prosthetic without a phantom. The body-image of the missing limb must be present. And when an amputee experiences an itch, scratching the prosthetic may relieve the annoying sensation. If an amputee sees his or her prosthetic foot immerse in water, the feeling of wetness may strangely ensue (Oliver Sacks, 1985; Ronald Melzack, 1997-2006.)
Even more startling, is that fact that multiple types of phantoms exist. While several may move, some are paralyzed; frozen stiff in unusual positions. Imagine an amputee with an extended phantom arm, turning sideways as he walks through doorways, in fear that his ghostly arm would hit the door frame. Many phantoms are like photocopies; exact replicas of the missing limbs. Others are grossly distorted and disproportioned. A phantom foot for example, may be disconnected from the leg and dangle in midair. Some phantoms will disappear and reappear at varying intervals. Sometimes these intervals last for decades. Interestingly, there are even phantom penises with phantom erections. Women may even experience one. It appears that while gender is determined by DNA (specifically the Y chromosome in male sperm) the sex of the brain appears to be determined by hormones that the embryo is exposed to in the womb. A man can have a female brain, and a woman can have a male brain. Suddenly the phrase, "a man in a women's body" or "a woman in a man's body" is not so far-fetched. (Vilayanur S. Ramachandran, 2004; Ronald Melzack, 1997-2006; Oliver Sacks, 1985.)
Unfortunately, some phantoms are also extremely painful. Pain that existed in a limb, prior to its amputation, may carry over into the phantom. Patients may feel the pain of an ingrown toenail or bunion that had been on a foot. Sometimes amputees report burning, cramping, and shooting sensations. Phantoms may curl up in uncontrollable spasms, or feel as though they are being prodded with a red-hot poker (Melzack, 1997-2000.) These terrible sensations may be relieved however, by using a mirror box invented by Dr. Ramachandran. A mirror box creates an illusion, that the missing limb has sprung to life, by using the mirror image of the intact limb. Subsequently, phantom pain will dissipate, or a frozen phantom will spring to life after years of paralysis.
Incredibly, the body maps of the brain will also cross-wire at the loss of sensory input. When a region of the primary somatosensory receiving area (S1) fails to continually represent a specific body part, neighboring regions take over. For example, a woman may experience orgasmic feelings in her missing foot, as the foot and genitalia regions in area (S1) are adjacent to each other. Once the neurons that represent the foot no longer fire, the genitalia region takes over (this may explain why there are foot fetishes, and why feet become erogenous zones.) Similarly, a man may experience stroking sensations in his missing hand when he shaves his face, as the head and hand regions are neighboring territories (Vilayanur S. Ramachandran, 2001-2004.)
According to Dr. Ramachandran, motor signals contribute to phantom limb phenomenon. The pre-motor and motor cortex are primarily responsible for voluntary movement. But when motor signals are sent to the muscles from these regions, a duplicate signal is sent to the parietal lobes as well, in a sort of feedback loop, thereby eliciting a ghostly sense of proprioception in the non-existent limbs.
Lastly, is the phenomenon of out-of-body experiences. By electrically stimulating the angular gyrus in the parietal lobes, the body-image can be decoupled from the physical body and take on a phantom existence of its own. One woman being treated for epileptic seizures by Dr. Olaf Blanke, a neurologist in Switzerland, felt herself fly out of her body and hang from the ceiling. Another woman being treated by Dr. Olaf Blanke, felt a phantom presence of a man behind her. The angular gyrus integrates visual and proprioceptive sensory streams, resulting in a coherent sense of self. But when the angular gyrus is stimulated with mild electrical currents, the two senses become decoupled, giving the perception of an out-of-body-experience.
As one can see, the self is a territory full of staggering perplexity and mystery. But it is a territory that will nonetheless be fully charted, perhaps within the next century. When the mind and the nature of self are completely unraveled, it will be the end to one of the greatest chapters in human history. It will be the end of the greatest journey; the journey in into the mind and our innermost selves.
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