**Core Concept**
Rivastigmine is a cholinesterase inhibitor used in the management of cognitive symptoms associated with neurodegenerative disorders. It works by increasing the concentration and duration of action of acetylcholine, a neurotransmitter involved in memory and learning.

**Why the Correct Answer is Right**
Rivastigmine is specifically indicated for the treatment of mild to moderate Alzheimer's disease. This is because Alzheimer's disease is characterized by a degeneration of cholinergic neurons in the brain, leading to a decrease in acetylcholine levels. By inhibiting the enzyme acetylcholinesterase, rivastigmine prevents the breakdown of acetylcholine, thereby enhancing cholinergic transmission and improving cognitive function. The drug has also been shown to have some efficacy in the treatment of Parkinson's disease dementia and Lewy body dementia.

**Why Each Wrong Option is Incorrect**
**Option A:** Depression is typically treated with a range of medications, including selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), and monoamine oxidase inhibitors (MAOIs). Cholinesterase inhibitors like rivastigmine are not a primary treatment option for depression.
**Option C:** Schizophrenia is treated with antipsychotic medications, which work by blocking dopamine receptors in the brain. Cholinesterase inhibitors are not a standard treatment for schizophrenia.
**Option D:** Obsessive-compulsive disorder (OCD) is typically treated with SSRIs or clomipramine, a tricyclic antidepressant with serotonergic activity. Cholinesterase inhibitors are not a primary treatment option for OCD.

**Clinical Pearl / High-Yield Fact**
Rivastigmine is a dual-action cholinesterase inhibitor, meaning it inhibits both acetylcholinesterase and butyrylcholinesterase, enzymes involved in the breakdown of acetylcholine and other cholinergic neurotransmitters. This dual action may contribute to its efficacy in treating cognitive symptoms associated with Alzheimer's disease.

**✓ Correct Answer: B. Alzheimer's disease**