Assignment: The Development of Brain Science

Assignment: Brain Science Development

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Assignment: The Development of Brain Science

1.3 The Development of Brain Science

Julien Jean Cesar Legallois is credited with providing the first evidence in support of localiza-tion of function in 1812 (Nanda, 2012). He was able to demonstrate that a specific area of the medulla controls breathing. In 1861 the French physician Paul Broca reported the results of a post- mortem examination of the brain of a man nicknamed “Tan” by other patients. Tan had suffered a stroke 2 decades earlier and had been able to utter only one syllable, “tan,” since the stroke. The autopsy that Broca performed on Tan’s brain revealed damage to a distinct area in the front por- tion of the left half of the brain (Figure 1.1). This area, today called Broca’s area after the French doctor who discovered it, is known to control the production of speech.

Figure 1.1: Broca’s area

Damage to Broca’s area typically results in disordered speech production.

Broca’s area (speech)

The Motor Cortex

Two German investigators, Gustav Fritsch and Eduard Hitzig, demonstrated in 1870 that specific areas of the motor cortex control particular movements of the body. When the investigators elec- trically stimulated the motor cortex near the top of the brain, a dog’s hind legs would wiggle. Stimulation of the motor cortex toward the bottom of the brain produced jaw movements.

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CHAPTER 1Section 1.3 The Development of Brain Science

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Motor cortex Sensory cortex

A Scottish physician, David Ferrier, documented the same findings in monkeys in 1876. In 1874 an American physician, Roberts Bartholow from Cincinnati, Ohio, stimulated the cortex of a female patient who had an extensive skull fracture following an accident. Bartholow was able to produce movements of specific muscles, depending on the placement of the stimulating probe on the woman’s exposed motor cortex (Valenstein, 1973).

This precise mapping of the body onto an area of the brain is called topographical organization. Figure 1.2 illustrates the topographical organization of the motor cortex in humans: this odd- shaped creature is called the motor homuculus. The motor cortex is organized in such a way that specific cells in the motor cortex control certain muscles in the body. Areas of the motor cortex near the top of the head command muscles in the feet and legs, whereas lower areas of the motor cortex command muscles in upper regions of the body. Ferrier’s research also showed that the somatosensory cortex, which is located next to the motor cortex, is topographically organized. Stimulation of different parts of the somatosensory cortex produces sensations in specific areas of the body (Figure 1.3). You will discover as you read this book that several areas of the brain display topographical organization.

Figure 1.2: Topographical organization of the human motor cortex

Specific regions of the motor cortex of the human brain control particular muscles in the body.

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CHAPTER 1Section 1.3 The Development of Brain Science

Figure 1.3: Topographical organization of the somatosensory cortex

Stimulation of specific regions of the sensory cortex of the human brain produces sensations in particular areas of the body.

Motor cortex Sensory cortex

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Soon after Ferrier reported his research on monkeys, scientific journals began to publish dozens of papers linking particular brain areas to specific behaviors. Despite the mounting evidence in support of localization, a number of highly regarded scholars refused to view the brain as anything more than an undifferentiated mass. As late as the 20th century, a prominent American psycholo- gist, Karl Lashley, conducted a number of experiments on rat learning and intelligence that he claimed demonstrated support for the concept of holism (Lashley, 1929).

Wilder Penfield’s Experiments

Wilder Penfield, a Canadian neurosurgeon, conducted experiments in the 1940s and 1950s on the exposed brains of awake but sedated patients while their skulls were open during surgery (Penfield, 1977). Using a 3-volt battery, he stimulated different areas of the cortex with a probe. Memories were elicited when some areas of the brain were stimulated. For example, patients would describe a childhood sweetheart or a room in an old home when areas toward the back of the cortex were excited. Stimulation in the somatosensory cortex produced sensations in various parts of the body, depending on the location of the electrical probe. In fact, it was this research by Penfield that inspired the drawings of the homunculi in Figures 1.2 and 1.3. Penfield’s work left no doubt that the brain is composed of many discrete regions that have specialized functions.