**Core Concept**
The midbrain is a crucial structure in the brainstem that plays a significant role in the integration of various reflexes, particularly those related to auditory and visual functions. The midbrain contains several nuclei that are responsible for the processing and integration of sensory information.

**Why the Correct Answer is Right**
The correct answer is related to the integration of the pupillary light reflex. The pupillary light reflex is a reflex that regulates the size of the pupil in response to changes in light intensity. The midbrain, specifically the Edinger-Westphal nucleus and the pretectal nucleus, plays a crucial role in the integration of this reflex. The Edinger-Westphal nucleus receives input from the optic nerve and sends signals to the ciliary ganglion, which then controls the pupil size. The pretectal nucleus receives input from the optic nerve and sends signals to the Edinger-Westphal nucleus to facilitate the pupillary light reflex.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the midbrain is not primarily associated with the integration of the corneal reflex.
**Option B:** This option is incorrect because the midbrain is not primarily associated with the integration of the vestibulo-ocular reflex.
**Option C:** This option is incorrect because the midbrain is not primarily associated with the integration of the gag reflex.

**Clinical Pearl / High-Yield Fact**
The pupillary light reflex is a critical reflex that is often tested in neurological examinations to assess the integrity of the optic nerve and the brainstem.

**Correct Answer: C. Pupillary light reflex**