The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human

Lastly, there is the dorsolateral prefrontal area. The DLF is required for holding things in your current, ongoing mental landscape, so you can use your ACC to direct attention to different aspects of the information and act according to your desires. (The technical name for this function is working memory.) The DLF is also required for logical reasoning, which involves paying attention to different facets of a problem and juggling abstractions—such as words and numbers—synthesized in the inferior parietal lobules (see Chapter 4). How and where the precise rules for this juggling arise is anybody’s guess.

The DLF also interacts with the parietal lobe. The two act jointly to construct a consciously experienced, animated body moving in space and time (which complements the insula-VMF pathway’s creation of a more viscerally felt anchoring of your self in your body). The subjective boundary between these two types of body image is somewhat blurred, reminding us of the sheer complexity of connections needed for even something as “simple” as your body image. This point will be driven home later; we will encounter a patient with a phantom twin next to him. Vestibular stimulation caused the twin to shrink and move. This implies powerful interactions between (a) vestibular input to the insula, which produces a visceral anchoring of the body, and (b) vestibular input to the right parietal lobe, which—along with muscle, joint sense, and vision—constructs a vivid sense of a consciously experienced, moving body.

Unity

What if the self is produced not by a single entity but by the push and pull of multiple forces of which we are largely unconscious? Now I’ll use the lenses of anosognosia and out-of-body experiences to examine the unity—and disunity—of the self.

HEMISPHERIC SPECIALIZATION: DOCTOR, I AM IN TWO MINDS

A great deal of pop psychology deals with the question of how the two hemispheres might be specialized for different roles. For example, the right hemisphere is thought to be more intuitive, creative, and emotional than the left, which is said to be more linear, rational, and Spock-like in its mentality. Many a New Age guru has used the idea to promote ways of unleashing the hidden potential of the right hemisphere.

As with most pop ideas, there is a kernel of truth to all this. In Phantoms in the Brain, I postulated that the two hemispheres have different, but complementary, coping styles in dealing with the world. Here I will consider the relevance of this to understanding anosognosia, the denial of paralysis seen in some stroke patients. Speaking more generally, it can help us understand why even most normal people—including you and me—engage in minor denials and rationalizations to cope with the stresses of our daily lives. What is the evolutionary function of these hemispheric differences, if any?

Information arriving through the senses is ordinarily merged with preexisting memories to create a belief system about yourself and the world. This internally consistent belief system, I suggest, is constructed mainly by the left hemisphere. If there is a small piece of anomalous information that doesn’t fit your “big picture” belief system, the left hemisphere tries to smooth over the discrepancies and anomalies in order to preserve the coherence of self and the stability of behavior. In a process called confabulation, the left hemisphere sometimes even fabricates information to preserve its harmony and overall view of itself. A Freudian might say that the left hemisphere does this to avoid shattering the ego, or to reduce what psychologists refer to as cognitive dissonance, a disharmony between different internal aspects of self. Such disconnects give rise to the confabulations, denials, and delusions that one sees in psychiatry. In other words, Freudian defenses originate mainly in the left hemisphere. In my account, however, unlike in orthodox Freudianism, they evolved not to “protect the ego” but to stabilize behavior and impose a sense of coherence and narrative to your life.

But there has to be a limit. If left unchecked, the left hemisphere would likely render a person delusional or manic. It is one thing to play down some of your weaknesses to yourself (an unrealistic “optimism” may be useful temporarily for forging ahead), but another thing to delude yourself into thinking you are rich enough to buy a Ferrari (or that your arm is not paralyzed) when neither is true. So it seems reasonable to postulate a “devil’s advocate” in the right hemisphere that allows “you” to adopt a detached, objective (allocentric) view of yourself.⁹ This right-brain system would often be able to detect major discrepancies that your egocentric left hemisphere has ignored or suppressed but shouldn’t have. You are then alerted to this, and the left hemisphere is jolted into revising its narrative.