Final answer:
The correct answer is option b. Excessive dopamine is associated with schizophrenia, while too little dopamine is associated with Parkinson's disease.
Step-by-step explanation:
Excessive dopamine is to Schizophrenia as too little dopamine is to Parkinson's disease.
Dopamine is a neurotransmitter that plays a crucial role in various brain functions. In schizophrenia, there is an overactivity of dopamine, which leads to the symptoms associated with the disorder. Antipsychotic medications are used to block dopamine receptors and decrease dopamine neurotransmission in order to treat schizophrenia.
On the other hand, Parkinson's disease is characterized by a lack of dopamine due to the death of dopamine-producing neurons. Treatments for Parkinson's disease aim to increase dopamine levels in the brain by providing L-DOPA, a precursor to dopamine.