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

A week later John’s father, Dr. Hamdi, was brought to my office by his wife. He had been a world-renowned professor of chemistry here at UC San Diego until his retirement three years earlier. About six months prior to my seeing him he sustained a skull fracture. In the emergency room at Scripps Clinic he was informed that a stroke, caused by a blood clot in his middle cerebral artery, had cut off the blood supply to the left hemisphere of his brain. Since the left hemisphere controls the right side of the body, Dr. Hamdi’s right arm and leg were paralyzed. Much more alarming than the paralysis, though, was the fact that he could no longer speak fluently. Even simple requests such as “I want water” required great effort, and we had to pay careful attention to understand what he was saying.

Assisting me in examining Dr. Hamdi was Jason Alexander, a medical student on a six-month rotation in our lab. Jason and I looked at Dr. Hamdi’s charts and also obtained a medical history from Mrs. Hamdi. We then conducted a routine neurological workup, testing in sequence his motor functions, sensory functions, reflexes, cranial nerves, and his higher mental functions such as memory, language, and intelligence. I took the handle of my knee hammer and, while Dr. Hamdi was lying in bed, stroked the outer border of his right foot and then the left foot, running the tip of the hammer handle from the pinky to sole. Nothing much happened in the normal foot, but when I repeated the procedure on the paralyzed right foot, the big toe instantly curled upward and all the other toes fanned out. This is Babinski’s sign, arguably the most famous sign in neurology. It reliably indicates damage to the pyramidal tracts, the great motor pathway that descends from the motor cortex down into the spinal cord conveying commands for volitional movements.

“Why does the toe go up?” asked Jason.

“We don’t know,” I said, “but one possibility is that it’s a throwback to an early stage in evolutionary history. The reflexive withdrawal tendency for the toes to fan out and curl up is seen in lower mammals. But the pyramidal tracts in primates become especially pronounced, and they inhibit this primitive reflex. Primates have a more sophisticated grasp reflex, with a tendency for the toes to curl inward as if to clutch a branch. It may be a reflex to avoid falling out of trees.”

“Sounds far-fetched,” said Jason skeptically.

“But when the pyramidal tracts are damaged,” I said, ignoring his remark, “the grasp reflex goes away and the more primitive withdrawal reflex emerges because it’s no longer inhibited. That’s why you also see it in infants; their pyramidal tracts haven’t fully developed yet.”

FIGURE 6.1 The two main language areas in the brain are Broca’s area (in the frontal lobes) and Wernicke’s area (in the temporal lobes). The two are connected by a band of fibers called the arcuate fasciculus. Another language area, the angular gyrus (not labeled in this figure), lies near the bottom of the parietal lobe, at the intersection of temporal, occipital, and parietal lobes.

The paralysis was bad enough, but Dr. Hamdi was more troubled by his speech impediment. He had developed a language deficit called Broca’s aphasia, named after the French neurologist Paul Broca, who first described the syndrome in 1865. The damage is usually in the left frontal lobe in a region (Figure 6.1) that lies just in front of the large fissure, or vertical furrow, that separates the parietal and frontal lobes.

Like most patients with this disorder, Dr. Hamdi could convey the general sense of what he was trying to say, but his speech was slow and effortful, conveyed in a flat monotone, filled with pauses, and almost completely devoid of syntax (loosely speaking, grammatical structure). His utterances were also deficient in (though not devoid of) so-called function words such as “and,” “but,” and “if,” which don’t refer to anything in the world but specify relationships between different parts of a sentence.

“Dr. Hamdi, tell me about your skiing accident,” I said.

“Ummmmm…Jackson, Wyoming,” he began. “And skied down and ummmmm…tumbled, all right, gloves, mittens, uhhhh…poles, uhhhh…the uhhhh…but the blood drained three days pass hospital and ummmmm…coma…ten days…switch to Sharpe [memorial hospital]…mmmmm…four months and back…ummmmmmm…it’s ummmmm slow process and a bit of medicine ummmmm…six medicines. One tried eight or nine months.”

“Okay continue.”

“And seizures.”

“Oh? Where was the blood hemorrhage from?”

Dr. Hamdi pointed to the side of his neck.