**Core Concept**
Subcortical dementia refers to a type of cognitive impairment characterized by deficits in executive function, memory retrieval, and mood regulation, with relatively preserved cortical functions such as language and visuospatial skills. This type of dementia is typically associated with subcortical structures, including the basal ganglia, thalamus, and brainstem.

**Why the Correct Answer is Right**
Subcortical dementia is often seen in conditions that affect the subcortical regions, such as Huntington's disease, multiple sclerosis, and vascular dementia. These conditions lead to damage or dysfunction in the subcortical structures, resulting in the characteristic cognitive and behavioral symptoms. For example, in Huntington's disease, the degeneration of the caudate nucleus and putamen leads to impaired executive function, memory retrieval, and mood regulation.

**Why Each Wrong Option is Incorrect**
**Option A:** Alzheimer's disease is an example of cortical dementia, characterized by progressive degeneration of the cerebral cortex, particularly the temporal and parietal lobes.
**Option B:** Frontotemporal dementia is a type of cortical dementia that primarily affects the frontal and temporal lobes, leading to changes in personality, behavior, and language.
**Option C:** Lewy body dementia is a type of cortical dementia characterized by the presence of Lewy bodies in the brain, leading to visual hallucinations, fluctuations in cognitive function, and parkinsonian motor symptoms.

**Clinical Pearl / High-Yield Fact**
Subcortical dementia often presents with a "slowing" of cognitive processes, with patients exhibiting difficulty with initiation, planning, and execution of tasks.

**Correct Answer:** C. Lewy body dementia is a type of cortical dementia.