colliculus

Colliculus, in neuroanatomy, refers to a pair of small hill-like structures on the dorsal midbrain. In mammals, the tectum contains two distinct colliculi on each side: the superior colliculus and the inferior colliculus. Collectively they form a four-piece auditory-visual integration center.

The superior colliculus is the rostral part of the tectum and is primarily involved in visual processing and the control of eye and head movements. It receives direct input from the retina and from cortical visual areas, and it integrates multisensory signals to orient the organism toward salient stimuli. Outputs from the superior colliculus reach brainstem regions that govern saccadic and gaze-related movements, contributing to reflexive orientation and spatial attention.

The inferior colliculus lies caudally and functions as a major relay center for auditory information. It receives input from brainstem auditory pathways, integrates sound localization cues, and projects to the thalamus, notably the medial geniculate nucleus, as part of the pathway to the cerebral cortex. This nucleus participates in processing of pitch, timing, and spatial attributes of sound, as well as in reflexive auditory responses.

Embryologically, the colliculi arise from the midbrain tectum and are conserved across vertebrates, reflecting a fundamental organization of sensory processing. Clinically, lesions can disrupt visually guided or reflexive orienting (superior colliculus) or auditory processing and localization (inferior colliculus), though the exact effects depend on the lesion’s size and location.