**Core Concept**
Deep brain stimulation (DBS) is a neurosurgical procedure that involves implanting an electrode in a specific area of the brain to modulate abnormal electrical activity. In the context of Parkinson's disease, DBS aims to alleviate motor symptoms such as tremors, rigidity, and bradykinesia.

**Why the Correct Answer is Right**
DBS for Parkinson's disease involves targeting the subthalamic nucleus (STN), a region involved in the basal ganglia circuitry. Stimulation of the STN has been shown to reduce the frequency of motor symptoms in Parkinson's disease by modulating the abnormal activity in the dopaminergic pathways. This is achieved by disrupting the hyperactivity of the STN, which is thought to contribute to the development of motor symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** The globus pallidus internus (GPi) is another target for DBS in Parkinson's disease, but it is not the primary target that has shown the most significant benefit in reducing motor symptoms.
**Option B:** The ventral intermediate nucleus (Vim) of the thalamus is a target for DBS in the treatment of essential tremor, not Parkinson's disease.
**Option C:** The pedunculopontine nucleus (PPN) is a target for DBS in the treatment of gait and balance disorders in Parkinson's disease, but it is not the primary target for reducing motor symptoms.

**Clinical Pearl / High-Yield Fact**
The subthalamic nucleus is a key target for DBS in Parkinson's disease, and stimulation of this area has been shown to significantly improve motor function and reduce symptoms in patients with advanced Parkinson's disease.

**Correct Answer: C. Subthalamic nucleus**