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Flocculonodular lobe

German: Lobus flocculonodularis

1 Definition

The flocculonodular lobe is a visible feature on the anteroinferior surface of the cerebellum as well as being its phylogenetically oldest part (archicerebellum).

2 Anatomy

The flocculonodular lobe of the cerebellum consists of the two flocculi and a central portion, the nodulus of the vermis. These three segments are separated from the posterior cerebellar lobe by the posterolateral fissure. The nodulus is connected to the two laterally positioned flocculi by the slender peduncles of the flocculi.

Afferents to the flocculonodular lobe come from the ipsilateral vestibular organ and the vestibular nuclei via the vestibulocerebellar tract, which passes through the inferior cerebellar peduncle. Visual afferents enter from the superior colliculi and from the visual cortex (the latter inputs having first been processed in nuclei of the pons).

Efferents from the flocculonodular lobe project to the cerebellum's fastigial nucleus as well as directly back to the vestibular nuclei.

3 Physiology

The flocculonodular lobe forms the vestibulocerebellum. It is primarily involved with balance equilibrium, but also uses information concerning head movements to influence eye movement. Important for this purpose are nerve impulses from the vestibular nuclei with information related to movements and the position of the head. After processing these data the flocculonodular lobe sends impulses that result in adjustments and stabilisation of eye movements.

Further processing of efferent signals from the flocculonodular lobe within the reticular formation and the vestibular nuclei lead to corrective signals for the axial musculature as well as for the extensors in the extremities in order to maintain a normal gait and balance equilibrium.

4 Clinic

Lesions of the flocculonodular lobe (e.g. by alcohol intoxication (reversible), or alcoholism (irreversible)) cause spontaneous nystagmus, jerky eye movements, disturbed balance equilibrium disequilibrium, gait and/or postural instability (vestibulocerebellar ataxia, astasia-abasia), negative Romberg's test, and truncal ataxia.

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