## **Core Concept**
The question pertains to the underlying neurochemical hypothesis of schizophrenia, specifically focusing on the cause of positive symptoms. Positive symptoms in schizophrenia include hallucinations, delusions, and disorganized thinking. These symptoms are primarily associated with an imbalance in dopamine neurotransmission.

## **Why the Correct Answer is Right**
The correct answer, **D. Dopamine hypothesis**, suggests that positive symptoms of schizophrenia are primarily due to an overactivity of dopamine pathways in the brain, particularly in the mesolimbic pathway. According to this hypothesis, excessive dopamine release or increased sensitivity of dopamine receptors leads to the manifestation of positive symptoms. This theory is supported by the fact that drugs that block dopamine receptors, such as antipsychotics, are effective in reducing these symptoms.

## **Why Each Wrong Option is Incorrect**
- **Option A:** The statement seems incomplete, but if it implies a lack of direct association with dopamine, it is incorrect because the dopamine hypothesis is a well-established theory for positive symptoms.
- **Option B:** Similarly, this option is incomplete but suggesting an alternative without specifying could mislead. If it implies another neurotransmitter without context, it's hard to assess, but dopamine is specifically implicated in positive symptoms.
- **Option C:** This option is also incomplete and cannot be directly assessed without further information. However, given the context, dopamine (option D) is specifically linked to positive symptoms.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that while dopamine dysregulation is associated with positive symptoms of schizophrenia, negative symptoms and cognitive deficits are more closely linked to abnormalities in other neurotransmitter systems, including glutamate and serotonin. The first-generation antipsychotics, which are potent dopamine D2 receptor antagonists, are particularly effective against positive symptoms.

## **Correct Answer: D. Dopamine hypothesis**