Self-Serve Brains: Personal Identity Veers to the Right Hemisphere

Article excerpt

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 Consider the man who, after sustaining serious brain damage, insisted that his parents, siblings, and friends had been replaced by look-alikes whom he had never met.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.

I SPY 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 "T" 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. …