Shufflebrain

But what about the mind after the loss of a visual lobe of the brain? Halstead's group had something to say about this, too. The twenty-two year old secretary had scored 133 points on an IQ test before surgery. A month after the operation, she again scored 133. And five weeks after the operation, she left the hospital and returned to her job--as a secretary, no less! About the filing clerk, whose IQ also remained unchanged, Halstead et al. wrote, "Immediately on awakening from the anesthetic, the patient talked coherently and read without hesitation. At no time was there any evidence of aphasia [speech loss] or alexia [reading deficits].

Thus, in spite of the loss of half the visual areas of their cerebrums, despite a halved, or nearly halved, view of the external world, both young women retained whole visual memories. They are far from unique. Three floors below where I sit, there is an eye clinic whose filing cabinets contain thousands of visual-field maps and case upon case documenting the survival of a complete human mind on the receiving end of severely damaged human visual pathways.

The structuralists attempted to dodge Halstead's evidence by insisting that visual cognition and memory must lie outside the occipital lobe--somewhere! Others just plain ignored it (and still do.)

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Nor is vision the sole brain function whose story begins true to an anatomist's expectations only to end in uncertainty. Take language. Certain speech and reading deficits correlate with damage to particular areas of the brain (and provide important diagnostic signs). Broca's motor speech aphasia most often results from blockage or hemorrhage of the arteries supplying the rear of the frontal lobe, and occurs on the left cerebral hemisphere about 80 to 85 percent of the time. In Broca's aphasia, a person understands language, communicates nonverbally, and writes, if not also paralyzed, but cannot articulate or speak fluently. (A sudden drop in fluency may, in fact, signal an impending stroke). In contrast, another speech aphasia is associated with damage to the temporal lobe. Known as Wernicke's aphasia, this malady is characterized not by apparent loss of fluency but by absence of meaning in what the person says. The words don't add up to informative sentences; or the person may have problems naming familiar objects, and call a cup an ashtray, for instance, or be unable to name a loved one.

Broca's and Wernicke's speech areas intercommunicate via a thick arching bundle (called the arcuate bundle). When damage to this pathway disconnects the two speech areas, language fluency and comprehension are not affected; however, the sufferer cannot repeat newly presented phrases.

Alexia, the inability to read, and its partial form, dyslexia, may suggest a tumor or arteriosclerosis in an area directly in front of the occipital lobe. Or, if a person begins to have problems writing down what he or she hears, a lesion may be developing in a span of brain between the occipital lobe and Wernicke's area.

In other words, anatomy functions in language as it does in vision. And those who tend to our health ought to be well informed about what a particular malfunction may portend. But aphasias do not supply evidence for a theory of mind. Damage to a specific cerebral area does not always produce the anticipated deficit. Individuals vary. Many malfunctions correlate with no detectable anatomical lesion (this is often true in dyslexia). And, whereas, massive cerebral damage (for instance, surgical removal of an entire cerebral hemisphere) may have only marginal effects on one person, a pin prick in the same area may destroy another's personality. Scientific law, qua law, cannot be founded on maybes and excuses. Yet in every bona fide case the structuralist has been able to make for the anatomy of memory, the holist has managed to find maybes-- and excuses. One of the best illustrations of this occurs in what is called "split-brain" research.

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The two cerebral hemispheres intercommunicate via a massive formation of nerve fibers called the corpus callosum. A splitting headache marks roughly where the corpus callosum crosses the midline (although pain signals travel along nerves in blood vessels and connective tissue wrappings of the brain). A feature of mammals, the corpus callosum develops in our embryonic brain as we start acquiring mammalian form. On occasion, however, a person is born without a corpus callosum.

In spite of its relatively large mass--four inches long, two inches wide, and as thick as the sole of a shoe--the corpus callosum received surprisingly little attention until the 1950s. But in the 1960s, it made the newspapers. When surgeons split the corpus callosum, they produced two independent mentalities within one human body.