2.8 The Hemispheres Work Together With Some Specialization

As mentioned earlier, the cortex is divided into the left hemisphere and the right hemisphere. Do the left and right hemispheres process different information? In study unit 2.4, you learned about Broca’s area and the relationship between the left hemisphere and language. For most people, the left hemisphere is responsible for logical thought and language. Being able to speak and write depends on the left hemisphere. By contrast, the right hemisphere is responsible for spatial relationships, such as understanding a map or locating objects that are around you. Recognizing faces, understanding emotional aspects of language, and abstract thinking involve more processing in the right hemisphere.

Studying people who have had brain surgery has helped us understand how the two hemispheres process information. When people have severe epilepsy that does not respond to medication, the corpus callosum can be severed, so that the two halves of the brain are almost completely isolated from each other. After the procedure, a seizure that begins in one hemisphere is less likely to spread throughout the cortex. The resulting condition, called split brain, has provided many important insights into the specialized functions of each brain hemisphere.

The hemispheres normally work together. Images from the left visual field (left half of what you are looking at) are processed by the right hemisphere. Images from the right visual field are processed by the left hemisphere (Figure 2.24). The left hemisphere also controls movements by the right side of the body, and the right hemisphere controls movements by the left side of the body. In addition, the left hemisphere also controls language processes (see Figure 2.12). In a healthy person, the corpus callosum lets the hemispheres communicate so that the right side of the brain knows what the left is doing and vice versa, and it also allows a person to speak about information processed in either hemisphere.

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The cross-sectional view of the brain shows the following parts: Right Hemisphere (better with spatial relationships and controls left-side body movements), Right hemisphere occipital lobe (processes left visual field information), Left hemisphere occipital lobe (processes right visual field information), Left Hemisphere (better with language and controls right-side body movements), left visual field and right visual field.

By contrast, in split-brain patients, the hemispheres are separated, so information cannot be transferred from one hemisphere to another. In these patients, each hemisphere works on its own. This split lets psychologists test the functions of the two hemispheres separately. In tests on the first people with split brains, Michael Gazzaniga and Nobel Laureate Roger Sperry (1967) came up with a stunning result: Just as the brain had been split in two, so had the conscious mind!

In one experiment (Gazzaniga & LeDoux, 1978), a split-brain patient saw two pictures flashed on a screen briefly at the same time. One image, a chicken foot, was shown to the right visual field. The other image, a snow-covered house, was shown to the left visual field (Figure 2.25a on p. 74). The patient was asked to respond to what was shown. To do so, the patient had to point each hand at the most related image in a row of items below the screen (Figure 2.25b). The left hemisphere, having processed the chicken foot, made the right hand point at a picture of a chicken head (Figure 2.25c). The right hemisphere, having processed the snowy house, made the left hand point at a picture of a snow shovel (Figure 2.25d).

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The illustration shows the participant sitting at a table. A picture of a house and a chicken’s leg is shown on the monitor. A snow doll and a tree are present in front of the house. Eight different pictures are placed in front of the participant. The participant selects two pictures showing a chicken and a shovel. A call-out near the left side of the participant’s head shows the picture of a chicken leg and a call-out near the right side of the participant’s head shows the picture of the house. The five stages in the activity are as follows: A split-brain participant watches as different images flash simultaneously on the left and right sides of a screen. Below the screen is a row of other images. The patient is asked to point each hand at an image most related to the image flashed on that side of the screen. The left hemisphere lets the right hand point at a picture of a chicken head. The right hemisphere lets the left hand point at a picture of a snow shovel. When the split-brain participant is asked to explain these selections, the left hemisphere can provide the answers verbally. To explain the right hand’s selection of the chicken head, the left hemisphere lets the participant say: “The chicken claw goes with the chicken head.” To explain the left hand’s selection of the shovel, the left hemisphere must interpret, because it does not see the snow scene, which is processed only in the right hemisphere. The left hemisphere interprets that the shovel is used to clean up after chickens and verbalizes this explanation.

Then the patient was asked to verbally explain these responses. Recall that the left hemisphere (or “left brain”) processes language. Therefore, the patient had no trouble explaining why his right hand pointed to the picture of the chicken head. The left hemisphere had processed the picture from the right visual field (the chicken claw), and so the patient could state that “the chicken claw goes with the chicken.”

What about the action of the patient’s left hand? Because the patient’s brain had been split, the right hemisphere had no access to language production. The left hemisphere had access to language but no information about the left hand’s actions, which it tried to make sense of. So the patient’s answer to why his left hand had pointed to the shovel was that “you need a shovel to clean out the chicken shed” (Figure 2.25e). The left brain could not verbalize the relationship between the shovel and the snowy house because the snow scene was processed only in the right hemisphere. Instead, the left hemisphere interpreted the left hand’s pointing to the shovel in a way that was consistent with the only knowledge available to the left brain: the chicken claw.

In other words, even with a split brain, the brain’s hemispheres work together to reconstruct our conscious experiences (de Haan et al., 2021). This happens because the left hemisphere tends to construct a world that makes sense. Thus the left hemisphere created an explanation for the left hand’s action, which had been performed by the independent right hemisphere in the split-brain patient (Gazzaniga, 2000). However, the left hemisphere’s explanation was unrelated to the right hemisphere’s real reason for commanding that action. Yet to the split-brain patient, the explanation seemed perfectly logical.

The Left Brain/Right Brain Myth You have probably heard the idea that some people are “left brain” logical types and others are “right brain” artistic types. According to this popular notion, people differ to the extent that their right or left hemisphere dominates their thinking styles. Left-brain thinkers are said to be more analytical, rational, and objective. Right-brain thinkers are said to be more creative and to view the world more holistically and subjectively. According to this thinking, a dominant left brain suppresses right-brain creativity, which suggests that people can become more creative and passionate by engaging more of their right hemisphere.

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The cover page of the first book reads Right brain, Left brain Reflexology. A self-help approach to Balancing Life’s Energies with color, sound, and Pressure-point Techniques by Madeleine Turgeon. The cover page of the second book reads The new Drawing on the right side of the Brain by Betty Edwards. A brand-new edition of the classic was expanded and updated. A course in enhancing creativity and artistic confidence. The cover image shows a side view of a young woman’s face. The cover page of the third book reads At left brain turn right. An uncommon path to shutting up your inner critic, giving fear the finger, and having an amazing life. A testimony about the book reads insightful and practical. An empowering book. By Academy Award winner, Olympia Dukakis. The cover image shows a brain. Several actions of the brain are listed in the left hemisphere whereas the right hemisphere is covered with lots of colors.

This false idea has permeated society. Multiple tests are available, particularly on the internet, to determine whether you are left- or right-brain dominant. Countless pop psychology books give advice on living better by emphasizing your particular brain style or drawing on the other side of your brain (Figure 2.26). However, the scientific evidence is overwhelming: People are neither left-brain nor right-brain dominant.

The hemispheres are specialized for certain functions, such as language or spatial relationships. However, each hemisphere is capable of carrying out most cognitive processes, though sometimes in different ways. Most cognitive processes involve the coordinated efforts of both hemispheres. A study that examined brain activity in over 1,000 individuals ages 7 to 29 found no differences between people in the extent to which their right or left hemisphere was active (Nielsen et al., 2013). In contrast to the idea that a liberated right brain helps a person learn better, some evidence suggests that the people who perform best at math are those whose two hemispheres work most closely together (Prescott et al., 2010).

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