lemniscus

Lemniscus, from the Latin for “little ribbon,” is a term used in neuroanatomy to describe a ribbon-like bundle of ascending sensory fibers within the brainstem. The most prominent lemnisci are the medial lemniscus and the lateral lemniscus, each carrying different types of sensory information to higher brain centers. The term can also reflect historical usage for other ascendant tracts, sometimes referred to as the spinal lemniscus.

The medial lemniscus is the principal tract of the dorsal column–medial lemniscus pathway. It originates from the dorsal column nuclei—the gracile and cuneate nuclei—in the medulla, where fibers cross (decussate) as internal arcuate fibers. The tract then ascends through the brainstem as the medial lemniscus to the ventral posterior lateral (VPL) nucleus of the thalamus. From the thalamus, third-order neurons project to the primary somatosensory cortex. This pathway conveys fine touch, vibration, and conscious proprioception from the body and limb.

The lateral lemniscus is an ascending auditory pathway that traverses the pons and medulla to the inferior colliculus in the midbrain. It receives input from the cochlear nuclei and superior olivary complex and contributes to the binaural processing of sound. The pathway continues via the brachia of the inferior colliculus to the medial geniculate nucleus of the thalamus, and onward to the auditory cortex. Damage to this tract can affect auditory perception on the side contralateral to the lesion.

In addition, historical usage sometimes describes a spinal lemniscus for pain and temperature fibers ascending to the thalamus, though modern anatomy more often refers to the spinothalamic system.