Endorphins are neurotransmitters linked to reduced pain and increased pleasure. They are natural, meaning that they are synthesized and exist in the body, and are released in response to external pain (e.g., endorphins are released when you hit your head). 

Damage to Broca's area causes expressive aphasia, or "Broca's aphasia." People who suffer from this type of aphasia are unable to form grammatical sentences fluidly; their speech is instead labored and halting. Because the patient is unable to form full sentences easily, he likely sustained injury to Broca's area.

We can tell that the patient did not injure Wernike’s area because we are told that he is still able to understand language. People who have Wernike's area injuries suffer from a different kind of aphasia, "receptive aphasia" or "Wernike's aphasia"; these individuals are not able to understand language, though they can form full sentences. One can think of expressive aphasia as a disruption of syntax that leaves semantics intact, and of receptive aphasia as a disruption of semantics leaving syntax intact.

None of the other answer choices are as specifically related to the abilities to produce and understand language as are Broca's area and Wernike's area; the basal ganglia helps to control motor functions and voluntary movements, the corpus callosum connects the left and right hemispheres of the brain, and the hippocampus helps regulate long-term memory.

The cerebellum, as well as the basal ganglia and motor cortex, are responsible for procedural, or muscle memory. Whereas the hippocampus is associated with semantic, spacial, and episodic memory, the cerebellum, basal ganglia, and motor cortex are associated with motor control. Procedural memory is also known as non-declarative or implicit (rather than explicit) memory because a person cannot say, but can demonstrate their acquisition of skill. For example, if an individual with a driver's license suffers an injury to their hippocampus and suffers from amnesia, they may still retain the ability to drive a car due to muscle memory in the cerebellum.

Cerebrospinal fluid is the fluid in and around the brain and spinal cord (the two components of the central nervous system) that serves as a protective barrier. 

Belyaev's selection may be considered as artificial selection because he was purposefully selecting for a specific behavioral trait—tameness. As a result, natural selection and genetic selection would be incorrect choices. There was no noted mutation observed in the study; therefore, mutagenesis would be an incorrect answer.

Neuroplasticity is a concept that refers to structural changes in the brain that occur because of changes in the person's behavior, emotions, thoughts, or environment. It means that the brain is more flexible and adaptable than once thought, even after fully developing. 

Conditioning can also part of learning a new task, but conditioning involves pairing stimuli together (e.g. classical conditioning) or being reinforced or punished (e.g. operant conditioning). Hemispheric specialization is when one side—hemisphere—of the brain is dominant in controlling a particular function. 

The sympathetic nervous system is at work in this scenario. Both the sympathetic and parasympathetic nervous systems are divisions of the autonomic nervous system. Unlike the parasympathetic nervous system; however, the sympathetic branch is the "fight or flight" response. In emergencies, the hypothalamus initiates this response which, dumps adrenaline into the blood stream and accelerates bodily functions for either a fight or flight scenario. The parasympathetic branch is the "rest and digest" system and works in opposition to the sympathetic branch.