Final answer:
The Nucleus accumbens is the most active brain region in terms of the reward experienced from a cocaine high, as it is a key part of the brain's reward system and is heavily stimulated by increased dopamine levels caused by cocaine.
Step-by-step explanation:
The brain region you would expect to be most active in terms of the reward a patient experiencing a cocaine high is experiencing is C. Nucleus accumbens. Cocaine acts as a stimulant by preventing dopamine reuptake by nerve cells, leading to increased levels of dopamine in synaptic clefts. The nucleus accumbens is part of the brain's reward circuit and is crucial for the reinforcing effects of drugs, including the euphoria associated with cocaine use. The presence of high dopamine levels in this area is thought to be responsible for the drug's addictive properties and the pleasure derived from its consumption.