Story of Psychology - Morton Hunt [65]
Similarly, Flourens found that the progressive removal of areas of the cortex in animals reduced their responses to sensory stimulation and their capacity to initiate action. A small lesion produced no specific effect, as it should have if phrenology were correct, but merely decreased the animal’s overall responsiveness to visual stimuli and its general level of activity. With more removal of the cortex, the animal would become more inert, until all responsiveness and self-initiated movement were gone; a totally decorticated bird, for instance, would not fly unless thrown into the air. Flourens concluded that perception, judgment, will, and memory were distributed throughout the cerebral cortex. Although he had found a gross localization of function in the brain—the cortex and the cerebellum did serve different purposes—the specific functions of each were apparently evenly distributed within each.
Gall’s pseudo-scientific theory thus led to the first experimental studies of the localization of brain functions. Moreover, his theory, though wrong in all its details, survived Flourens’s assault, since later cognitive neuroscientists, following Flourens’s lead, were able to identify particular areas of the brain as being responsible for visual perception, auditory perception, and motor control. Flourens was right that memory and thinking are distributed throughout the cortex, but a number of lower and even some higher mental processes are indeed localized.
The most striking instance of a high-level function carried out by a local area of the brain is language. In 1861, Leborgne, a fifty-one-year-old patient at the Bicêtre asylum in Paris, was transferred to the surgical ward, suffering from gangrene in his right leg. The surgeon, a young man named Paul Broca, questioned the patient about his ailment, but Leborgne could utter nothing in reply but the meaningless sound “tan. ”10 He communicated only by gestures and “tan, tan,” although if one failed to understand his gestures he could angrily blurt out, “Sacré nom de Dieu!” Broca learned that Tan, as he was known in the hospital, had come to the asylum twenty-one years earlier, when he lost the power of speech. He had remained otherwise intellectually normal, but after some years had slowly developed paralysis of the right arm and leg.
Tan died six days after arriving at the surgical ward. Broca performed an autopsy and found that an egg-sized area of the left side of the brain somewhat forward of the middle had been destroyed; there was almost no tissue in the center of the lesion, and around its edges the remaining tissue was softened. Based on Leborgne’s history, Broca concluded that the lesion had begun at what was now its center and that while it was still relatively small, it had completely destroyed Leborgne’s ability to speak; only later did its spread cause paralysis. Evidently, this small frontal-lobe area of the left hemisphere of the brain was the seat of speech. It has been known ever since as Broca’s Area.
A little over a dozen years later, a German physician, Carl Wernicke, similarly discovered that certain patients who spoke fluently but used many peculiar words and had difficulty understanding what was said to them had a lesion of another small area in the left hemisphere a few inches to the rear of Broca’s Area. It eventually became clear that Broca’s Area governs syntax (the structure of speech) and Wernicke’s Area, as the second one is known, semantics (the meaning of words). Both are needed for normal speech; a lesion of Broca’s