Question

Consider an individual who had been fluent in American Sign Language before suffering an injury to his left cerebral hemisphere. After the injury, he could still understand that sign language but could not readily generate sign language that represented his thoughts. Propose two hypotheses that could explain this finding. How might you distinguish between them?

Short answer

The conditions of the individual suggest that he had encountered an injury in the cerebrum’s Broca area and developed Broca’s aphasia. It can also be hypothesized that the individual developed Parkinson’s disease.

If the individual suffers from Broca’s aphasia, they would only have difficulty generating sign languages. In contrast, if the individual has Parkinson’s disease, they would have overall difficulty in motor movement accompanied by tremor and postural changes.

Step-by-step solution

Nervous system

The nervous system refers to an organism’s control center; this organ system monitors, processes, and regulates all the activities of the body. The nervous system is broadly grouped as peripheral (PNS) and central nervous systems (CNS).

The brain

The organ of the nervous system (specifically, the CNS), which is responsible for all the controlling actions, is referred to as the brain. This organ is situated at the topmost region of the body, and different regions of the brain are specialized for the control of different body functions.

Explanation of the injury

The individual suffered an injury to the left cerebral hemisphere, and due to this, they lost the ability to generate sign language or represent their thoughts. There can be two possible explanations for this symptom.

The injury might have affected the Broca region, which is known for controlling speech production and gestures related to speech. As a result, the person develops Broca’s aphasia and could follow speech but is unable to generate them.

The disfunction in the generation of sign language can also be due to the development of Parkinson’s disease.The injury might have affected the motor cortex neurons and caused an inability to generate sign languages as motor activities are hampered.

Among the two possible causes (Parkinson’s disease and Broca’s aphasia), the Broca’s area will display difficulty only in generating sign language, and other motor activities will be unaffected. In contrast, Parkinson’s disease would affect the overall functioning of the limbs and cause tremors.