**Core Concept**
Stereoanesthesia is a condition characterized by the loss of ability to perceive three-dimensional space and the spatial relationships between objects. This is a complex sensory deficit that affects a person's ability to judge distances, depths, and spatial orientation.

**Why the Correct Answer is Right**
Stereoanesthesia is primarily due to lesions affecting the cerebral cortex, specifically the areas involved in processing visual and spatial information. The primary visual cortex (V1) and secondary visual cortex (V2) are crucial for processing binocular disparity, which is essential for depth perception. Additionally, the parietal lobe, particularly the intraparietal sulcus (IPS), plays a significant role in integrating visual and spatial information to create a three-dimensional representation of the environment. Damage to these areas can result in stereoanesthesia.

**Why Each Wrong Option is Incorrect**
**Option A:** Nucleus Gracilis is primarily involved in transmitting tactile and proprioceptive information from the lower body to the thalamus, and lesions here would not primarily cause stereoanesthesia.

**Option B:** Nucleus cuneatus is involved in transmitting tactile and proprioceptive information from the upper body to the thalamus, similar to nucleus gracilis, and lesions here would not primarily cause stereoanesthesia.

**Option D:** The spinothalamic tract is primarily involved in transmitting pain and temperature information from the body to the thalamus, and lesions here would not primarily cause stereoanesthesia.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that stereoanesthesia can result from various lesions, including those affecting the visual cortex, parietal lobe, or even the corpus callosum, which can disconnect the two hemispheres and impair inter-hemispheric communication necessary for spatial processing.

✓ Correct Answer: C. Cerebral cortex