Flocculus

At a glance

English

Flocculus

Latin (TA2)

Flocculus

System

Brain and spinal cord

Region

Head

Side

Paired, left and right

About the flocculus

The flocculus (Latin for a little tuft of wool) is a small, irregular piece of cerebellar cortex on the anterior part of the inferior surface of each hemisphere. It lies against the back of the middle cerebellar peduncle, close to where the vestibulocochlear and facial nerves enter the brainstem, and in front of the biventral lobule. A thin white stalk, the floccular peduncle, joins it to the nodule of the vermis in the midline. Together the two flocculi and the nodule form the flocculonodular lobe, the oldest part of the cerebellum, often called the vestibulocerebellum.

Its inputs come largely from the vestibular system. Mossy fibres arrive directly from the vestibular nerve and from the vestibular nuclei, and others come from the pontine nuclei and the nucleus reticularis tegmenti pontis, carrying visual and motion signals. Climbing fibres from the inferior olive carry error signals that drive learning. The flocculus is often described as having caudal and rostral halves with somewhat different inputs, and its Purkinje cells are grouped in parallel zones. Unlike most cerebellar cortex, many of its Purkinje cells send their axons straight to the brainstem, mainly to the superior and medial vestibular nuclei, rather than through a deep cerebellar nucleus; one zone projects to the interposed nucleus.

Its chief job is to keep the gaze steady. It tunes the vestibulo-ocular reflex, which moves the eyes opposite to the head so that the image stays still on the retina, and it can recalibrate the gain of that reflex when vision changes, for example with new spectacles. It also helps smooth pursuit of a moving target and holding the eyes in an off-centre position. Through the vestibular nuclei it contributes to posture and balance.

Damage to the flocculus or the flocculonodular lobe, as with a midline tumour in a child (medulloblastoma) or with alcohol intoxication, gives a characteristic pattern: smooth pursuit breaks up into jerky catch-up saccades, the eyes drift back from an eccentric position with gaze-evoked nystagmus, the reflex cannot adapt, and there may be unsteadiness of stance and gait. Vertigo, nausea and vomiting can accompany it.

Function and supply

Function

Controls and adapts the vestibulo-ocular reflex, smooth pursuit and gaze holding, and helps balance through its output to the vestibular nuclei.

Blood supply

Anterior inferior cerebellar artery.