Personal identity veers to the right hemisphere
The concept of identity theft assumes an entirely new meaning for people with brain injuries that rob them of their sense of self—the unspoken certainty that one exists as a person in a flesh—bounded body with a unique set of life experiences and relationships. Consider the man who, after sustaining serious brain damage, insisted that his parents, siblings, and friends had been replaced by look-alikes whom he had never met. Everyone close to him had become a familiar-looking stranger. Another brain-injured patient asserted that his physicians, nurses, and physical therapists were actually his sons, daughters-in-law, and coworkers. He identified himself as an ice skater whom he had seen on a television program.
The sense of "I" can also go partially awry. After a stroke had left one of her arms paralyzed, a woman reported that the limb was no longer part of her body. She told a physician that she thought of the arm as "my pet rock."
Other patients bequeath their physical infirmities to phantom children. For instance, a woman blinded by a brain tumor became convinced that it was her child who was sick and blind, although the woman had no children.
These strange transformations and extensions of personal identity are beginning to yield insights into how the brain contributes to a sense of self, says neuroscientist Todd E. Feinberg of Beth Israel Medical Center in New York City. Thanks to technology that literally gets inside people's heads, researchers now are probing how the brain contributes to a sense of self and to perceptions of one's body and its control. Scientists expect that their efforts to shed light on the vexing nature of consciousness, as well as on the roots of mental disorders, such as schizophrenia, characterized by disturbed self-perception.
Scholars have argued for more than 300 years about whether a unified sense of self exists at all. A century ago, Sigmund Freud developed his concept of ego, a mental mechanism for distinguishing one's body and thoughts from those of other people. Around the same time, psychologist William James disagreed, writing that each person's "passing states of consciousness" create a false sense that an "I" or an ego runs the mental show.
Researchers still debate whether the self is the internal engine of willful behavior or simply a useful fiction that makes a person feel responsible for his or her actions. Some investigators argue that each person harbors many selves capable of emerging in different situations and contexts.
Regardless of philosophical differences, Feinberg notes, evidence suggests that the brain's right hemisphere often orchestrates basic knowledge about one's self, just as the left hemisphere usually assumes primary responsibility for language.
Disorders of the self caused by brain damage fall into two main categories, Feinberg proposes. Some patients lose their personal connection to significant individuals or entities, such as the man who thought everyone he knew was a familiar stranger and the woman who regarded her lifeless arm as a pet rock. Other patients perceive personal connections where they don't exist, such as the man who saw his medical caretakers as family and coworkers and the woman who mentally conceived a phantom daughter.
In both categories, Feinberg says, "right brain damage is much more likely than left brain damage to cause lasting disturbances of the normal relationship between individuals and their environments."
Other neuroscientists take a similar view. According to brain-imaging studies conducted by researchers including Jean Decety and Jessica A. Sommerville, both of the University of Washington in Seattle, during the past 3 years, a right brain network located mainly in the frontal lobe organizes neural efforts aimed at discerning one's body and thoughts. That network overlaps a brain circuit that plays a role in identifying others, perhaps contributing to the two-sided nature of the self as "special and social, unique and shared," Decety and Sommerville said in a seminal 2003 article.
The right me
In order to coordinate the relationship between the self and the world, the brain takes sides, according to work by Feinberg and Julian Paul Keenan of Montclair State University in New Jersey. They analyzed patterns of brain damage in 29 previously published cases of disordered selves. Injury to the frontal region of the right hemisphere occurred in 28 people, compared with left-frontal damage in 14.
Ten of the patients had also incurred injuries to other parts of the right brain, compared with three individuals who displayed damage in other left brain areas, Feinberg and Keenan report in the December 2005 Consciousness and Cognition. Research in the past decade on the recognition of one's face reached similar conclusions. In a study directed by Keenan, adults with no known brain impairment viewed images that gradually transformed from their own faces into the face of a famous person such as Marilyn Monroe or Bill Clinton. Participants alternated using their left or right hands to hit keys that indicated whether they saw themselves or a famous person in each composite image.
When responding with their left hands, volunteers identified themselves in composite images more often than when they used their right hands. Since each side of the brain controls movement on the opposite side of the body, the left-handed results implicated the right brain in self-recognition.
Similar findings came from epileptic patients who underwent a medical procedure in which one brain hemisphere at a time was anesthetized. Keenan and his colleagues showed each patient an image that blended features of his or her own face with facial features of a famous person and later asked whose face the patient had seen. When tested with only the right brain awake, most patients reported that they had seen their own faces. When only the left brain was active, they usually recalled having seen the famous face.
A brain-scan investigation of 10 healthy adults, published in the April 15, 2005 NeuroImage, also implicates the right hemisphere in self-recognition. A team led by Lucina Uddin of the University of California, Los Angeles showed volunteers a series of images that, to varying degrees, blended their own faces with those of same-sex coworkers. Participants pressed keys indicating whether they saw themselves or a coworker in each image.
Pronounced blood flow, a sign of heightened neural activity, appeared in certain parts of the right hemisphere only when the participants recognized themselves, Uddin's group reports. Previous studies in monkeys indicated that these areas of the brain contain so-called mirror neurons, which respond similarly when an animal executes an action or observes another animal perform the same action
A right brain network of these mirror neurons maintains an internal self-image for comparison with faces that one sees, Uddin and her colleagues propose.
Still, not everyone regards the right brain as central to the self. Todd F. Heatherton of Dartmouth College in Hanover, N.H., and his coworkers reported in 2003 on a patient who had had surgery to disconnect the bundle of nerve fibers that connects the neural hemispheres. That split-brain patient recognized himself in images that blended his features with those of one of the researchers only when the images appeared in his right visual field and were thus handled by his left brain.
"Recognition of the self is one of the most basic, yet poorly understood, cognitive operations," Uddin says.
Chris Frith, a neuroscientist at University College London, has long wondered why people diagnosed with schizophrenia often experience their own actions as being controlled by others. A person with this severe mental disorder may report, for example, that space aliens ordered him to behave destructively.
Fifteen years ago, Frith thought that schizophrenia robbed people of the ability to monitor their intentions to act. If their behavior came as a complete surprise, they might attribute it to external forces.
Frith abandoned that idea after reading neurologists' reports of a strange condition called anarchic-hand syndrome. Damage to motor areas on one side of the brain leaves these patients unable to control the actions of the hand on the opposite side of the body. For example, when one patient tried to soap a washcloth with his right hand, his left hand, much to his chagrin, kept putting the soap back in its dish. Another patient used one hand to remove the other from doorknobs, which it repeatedly grabbed as he walked by doors.
Despite being unaware of any intention to use a hand in these ways, anarchic-hand patients don't experience their behavior as controlled by space aliens or another outside entity—they just try to correct their wayward hands.
Frith now suspects that anarchic-hand syndrome and schizophrenia's delusions of being controlled by others share a neural defect that makes it seem like one's movements occur passively. However, people with schizophrenia mistakenly perceive the passive movements as having been intentional.
In support of this possibility, Frith and his colleagues find that when shown scenes of abstract shapes moving across a computer screen, patients with schizophrenia, but not mentally healthy volunteers, attribute good and bad intentions to these shapes. Patients with schizophrenia may monitor their own actions in excruciating detail for signs of external control, Frith suggests.
In general, people rarely think about their selves but act as if such entities must exist. "The normal mark of the self in action is that we have very little experience of it," Frith says.
Harvard University psychologist Daniel Wegner goes further. Expanding the view of William James, Wegner argues that the average person's sense of having a self that consciously controls his or her actions is an illusion. This controversial proposal builds on an experiment conducted more than 20 years ago by neurophysiologist Benjamin Libet of the University of California, San Francisco.
Libet found that although volunteers' conscious decisions to perform a simple action preceded the action itself, they occurred just after a distinctive burst of electrical activity in the brain signaled the person's readiness to move. In other words, people decided to act only after their brains had unconsciously prepared them to do so.
Wegner has since performed experiments demonstrating the ease with which people claim personal responsibility for actions that they have not performed. In one study, participants looked in a mirror at the movements of an experimenter's arms situated where their own arms would be. When the arms moved according to another researcher's instructions, volunteers reported that they had willed the movements.
Feinberg says that these findings offer no reason to write off the self as a mental mirage.
A young woman stands in neuroscientist J. Henrik Ehrsson's laboratory at London's University College and places her palms on her waist. Cuffs placed over her wrists begin to vibrate tendons just under the skin, creating the sensation that her hands are bending inward. At the same time, the woman feels her waist and hips shrink by several inches to accommodate the imagined hand movements. Dr. Ehrsson's illusory instant-waist-loss program lasts only about 30 seconds.
Ehrsson and his coworkers used a brain-imaging machine to measure blood flow in the brains of 24 people as they experienced this illusion. Parts of the left parietal cortex, located near the brain's midpoint, displayed especially intense activity as volunteers felt their waists contract, the scientists report in the December 2005 PloS Biology.
The greater the parietal response, the more waist shrinkage the individual reported.
The scientists suspect that the activated parietal areas integrate sensory information from different body parts, a key step in constructing an internal image of one's body size and shape. When the brain receives a message that the hands are bending into the waist, it adjusts the internal body image accordingly, Ehrsson's team hypothesizes.
The brain can adjust its internal body map in a matter of minutes, the experiment demonstrates. Researchers who similarly induced illusions of expanding fingers came to that same conclusion.
The possibility that the brain can redraw body image in dramatic ways resonates with neuroscientist Miguel A.L. Nicolelis of Duke University Medical Center in Durham, N.C., and his colleagues. They've found that after monkeys learn to alter their brain activity to control a robotic arm, the animals' brains show the same activity pattern as when they move their own limbs.
Nicolelis' team reported in 2003 that the researchers had implanted electrodes in the frontal and parietal lobes of the brains of two female rhesus monkeys that used a joystick to control a cursor on a computer screen. That action maneuvered a robotic arm in another room. The animals gradually learned to modulate their brain signals to reposition the cursor, without moving a muscle.
Electrode data show that, after training, many neurons that formerly emitted synchronized signals as the monkeys manually manipulated the joystick to control the robotic arm also did so when the animals performed the same task mentally. Those results appeared in the May 11, 2005 Journal of Neuroscience.
The monkeys assimilated into their neural self-images a tool that they had learned to use proficiently, Nicolelis suggests. Apes and people possess an even stronger capacity for integrating tools into the brain's definition of self, in his view. This process may underlie the acquisition of expertise.
. "Our brains' representations of our bodies are adaptable enough to incorporate any tools that we create to interact with the environment, from a robot appendage to a computer keyboard or a tennis racket," Nicolelis says.
Despite the proliferation of such studies, the self's special status in the brain is far from assured. After reviewing relevant brain imaging and psychology studies, neuroscientists Seth J. Gillihan and Martha J. Farah, both of the University of Pennsylvania in Philadelphia, found little compelling evidence for brain networks devoted solely to physical or psychological aspects of the self.
At most, work such as Feinberg's with brain-damaged patients indicates that singular brain networks distinguish between one's limbs and those of other people, the researchers say. There are also suggestions that other brain areas foster a sense of control over one's limb movements, Gillihan and Farah reported in the January 2005 Psychological Bulletin.
Still, much of what we typically think of as "the self" may not be assignable to brain states or structures, in their view.
Feinberg argues that each of the increasingly complex levels of the brain—including the brain stem, the limbic system, and the cortex—contributes to intentional actions and to perceiving meaning in the world, the main ingredients of an "inner I."
Brain-damaged patients vividly illustrate the self's resiliency, Feinberg adds. While injury to the right frontal brain transforms some patients' identities in odd ways, other comparably injured patients somehow maintain their old selves.
A person's coping style and emotional resources usually influence responses to right brain damage, according to Feinberg's clinical observations. For example, one patient, a young man living half a world away from his family, referred to his paralyzed left arm as his brother's arm.
Feinberg asked the man what it meant to him to possess his sibling's arm rather than his own. "It makes me feel good," the man responded, in a voice choked with emotion. "Having my brother's arm makes me feel closer to my family."