## **Core Concept**
Supranuclear palsy of the hypoglossal nerve involves damage to the corticobulbar tracts that control the hypoglossal nerve (cranial nerve XII), which is responsible for tongue movements. This condition affects the motor control of the tongue but spares the nucleus and peripheral parts of the nerve.

## **Why the Correct Answer is Right**
In supranuclear palsy of the hypoglossal nerve, the weakness of the tongue is typically contralateral to the lesion because the corticobulbar tracts controlling the hypoglossal nerve are primarily crossed. This results in difficulty moving the tongue to the opposite side. However, the key feature that distinguishes supranuclear from nuclear or infranuclear lesions is that supranuclear lesions spare the reflexes. Therefore, the absence of a specific symptom or sign related to reflexes or certain types of tongue movements helps in identifying the correct exception.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Difficulty in protruding the tongue to the opposite side is a feature of supranuclear palsy because the corticobulbar inputs to the hypoglossal nucleus are mainly crossed, leading to weakness of the contralateral tongue muscles.
- **Option B:** Loss of associated movements of the tongue (like during swallowing or speaking) can occur due to the disruption of corticobulbar pathways that coordinate these movements.
- **Option C:** Spasticity of the tongue might not be a commonly described feature but weakness and changes in coordination are well-recognized.
- **Option D:** Preservation of the gag reflex and other brainstem reflexes involving the tongue is characteristic because supranuclear lesions do not affect the lower motor neuron pathways or the brainstem reflex arcs.

## **Clinical Pearl / High-Yield Fact**
A crucial clinical distinction is that in supranuclear lesions, the **gag reflex remains intact** because the afferent and efferent pathways of the gag reflex are not affected. This intact reflex helps differentiate supranuclear from nuclear or infranuclear hypoglossal nerve lesions.

## **Correct Answer:** D.