**Core Concept:** Visual hallucinations are visual perceptions that occur in the absence of corresponding external stimuli. Lesions in specific brain regions can lead to various types of hallucinations, including formed visual hallucinations.

**Why the Correct Answer is Right:** The correct answer lies in understanding the role of specific brain regions in processing visual information. These regions include the occipital lobe, which is primarily responsible for vision processing, and the parietal lobe, which is involved in spatial perception and attention.

**Why Each Wrong Option is Incorrect:**

A. **Incorrect:** Lesions in the parietal lobe can result in sensory deficits, like loss of touch or pain perception, but not formed visual hallucinations.

B. **Incorrect:** Lesions in the temporal lobe may cause auditory hallucinations, not visual ones.

C. **Incorrect:** Lesions in the frontal lobe can lead to cognitive deficits but not specifically formed visual hallucinations.

D. **Incorrect:** Lesions in the basal ganglia are associated with movement disorders, not visual hallucinations.

**Clinical Pearl:** Understanding the specific brain regions involved in vision processing can help distinguish between different types of hallucinations and aid in formulating a differential diagnosis for patients with neurological symptoms.

**Correct Answer:** C. Lesions in the occipital lobe result in visual hallucinations, including formed visual hallucinations. The occipital lobe, along with the adjacent areas like the calcarine cortex, plays a crucial role in processing visual information and presenting visual images to the conscious mind. Damage to these areas can disrupt this process, leading to visual hallucinations.