A 40-year-old man loses his right hand in a farm accident.Four years later, he has episodes of severe pain in the missinghand (phantom limb pain). A detailed PET scan study of hiscerebral cortex might be expected to showA. expansion of the right hand area in his right primarysomatosensory cortex.B. expansion of the right hand area in his left primarysomatosensory cortex.C. a metabolically inactive spot where his hand area in his leftprimary somatosensory cortex would normally be.D. projection of fibers from neighboring sensory areas into theright hand area of his right primary somatosensory cortex.E. projection of fibers from neighboring sensory areas into theright hand area of his left primary somatosensory cortex

The correct answer is E. Projection of fibers from neighboring sensory areas into the right hand area of his left primary somatosensory cortex.

Here's why:

1. The primary somatosensory cortex is the main sensory receptive area for the sense of touch and is located in the parietal lobe of the brain.

2. In the case of a person who has lost a limb, the brain undergoes a process called neuroplasticity, where it reorganizes itself by forming new neural connections.

3. The area of the brain that was receiving input from the lost limb (in this case, the right hand) no longer receives that input. As a result, the neighboring areas in the brain (those responsible for the arm, for example) may start to invade that territory, sending their own signals into the area that was once receiving input from the hand.

4. Since the right hand is controlled by the left hemisphere of the brain, the changes would be seen in the left primary somatosensory cortex.

5. Therefore, a detailed PET scan study of his cerebral cortex might be expected to show projection of fibers from neighboring sensory areas into the right hand area of his left primary somatosensory cortex. This could be the cause of the phantom limb pain, as the brain is still receiving (now incorrect) signals and interpreting them as coming from the missing hand.