FOCUS ON RESEARCH The Case of the Disembodied Woman
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FOCUS ON RESEARCH The Case of the Disembodied Woman
67 The Central Nervous System: Making Sense of the World Central sulcus Frontal lobe JAW K HIP TRUN E KNE ANKLE EYEB ALL VO CA LIZ AT ION IVA TIO N WIN EYE NOS E Left hemisphere G SWA Motor areas (end view) FIGURE IND TOES LLO NG TO WIN G UE B CHE HEAD SHOULDER ARM ELBOW RM FOREA T WRIS SAL Parietal lobe D HAN TLE LIT G RIN DLE D MI LIPS ELBOW FACE UM SHOULDER NE CK BRO W EYEL ID A ND WRIST HAND LE LITT G RIN LE D MID EX IND TH Somatosensory cortex 2.11 Motor and Somatosensory Cortex The areas of cortex that move parts of the body (motor cortex) and receive sensory input from body parts (somatosensory cortex) appear in both hemispheres of the brain. Here we show cross-sections of only those on the left side, looking from the back of the brain toward the front. Areas controlling movement of neighboring parts of the body, such as the foot and leg, occupy neighboring parts of the motor cortex. Areas receiving input from neighboring body parts, such as the lips and tongue, are near one another in the sensory cortex. Notice that the size of these areas is uneven; the larger the area devoted to each body part, the larger that body part appears on the “homunculus.” NECK TRUNK HIP Motor cortex TH EX UM B LEG FOOT TOES GENITALIA Left hemisphere FACE UPPER LI P LIPS Corpus callosum LOWER LIP W AND JA GUMS, TEETH, E U L G TON YNX INA OM R BD PHA A RA INT Corpus callosum Sensory areas (end view) Note: Did you notice the error in this classic drawing? (The figure shows the right side of the body, but the left hand and left side of the face.) Source: Penfield & Rasmussen (1968). In fact, the actual process is quite complex. Recall again your sleepy reach for the coffee pot. To grasp its handle, your cortex must first translate the pot’s location into a position relative to your body—to your left or right, for example. Next, the cortex must determine which muscles must be contracted to produce the desired movement toward that exact position. Groups of neurons work together to produce just the right combinations of direction and force in particular muscle groups. Making these determinations involves many interconnected areas of the cortex. Computer models of neural networks are showing how these complex problem-solving processes might occur (Graziano, Taylor, & Moore, 2002; Krauzlis, 2002). FOCUS ON RESEARCH Neurologist Oliver Sacks described the case of “Christina,” a woman who had somehow lost The Case of the Disembodied the ability to feel the position of her own body (Sacks, 1985). This case study led to imporWoman tant insights about biological psychology that could not be studied through controlled experiments. It showed, for example, that the sense known as kinesthesia (pronounced “kin-es-THEE-see-uh”) not only tells us where our body parts are but also plays an important role in our sense of self. Christina was a healthy young woman who entered a hospital in preparation for some minor surgery. Before the surgery could be performed, however, she began to have difficulty holding onto objects. Then she had trouble moving. She would rise from bed and flop onto the floor like a rag doll. Christina seemed to have “lost” her body. She felt