The flocculus (

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

: ''tuft of wool'', diminutive) is a small lobe of the

cerebellum The cerebellum (: cerebella or cerebellums; Latin for 'little brain') is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as it or eve ...

at the posterior border of the middle cerebellar peduncle anterior to the biventer lobule. Like other parts of the cerebellum, the flocculus is involved in motor control. It is an essential part of the

vestibulo-ocular reflex The vestibulo-ocular reflex (VOR) is a reflex that acts to stabilize Gaze (physiology), gaze during head movement, with eye movement due to activation of the vestibular system, it is also known as the cervico-ocular reflex. The reflex acts to im ...

, and aids in the learning of basic motor skills in the brain. It is associated with the nodulus of the

vermis The cerebellar vermis (from Latin ''vermis,'' "worm") is located in the medial, cortico-nuclear zone of the cerebellum, which is in the posterior fossa of the cranium. The primary fissure in the vermis curves ventrolaterally to the superior s ...

; together, these two structures compose the vestibular part of the cerebellum. At its base, the flocculus receives input from the inner ear's vestibular system and regulates balance. Many floccular projections connect to the motor nuclei involved in control of eye movement.

Structure

The flocculus is contained within the flocculonodular lobe which is connected to the cerebellum. The cerebellum is the section of the brain that is essential for

motor control Motor control is the regulation of movements in organisms that possess a nervous system. Motor control includes conscious voluntary movements, subconscious muscle memory and involuntary reflexes, as well as instinctual taxes. To control ...

. As a part of the cerebellum, the flocculus plays a part in the vestibulo-ocular reflex system, a system that controls the movement of the eye in coordination with movements of the head. There are five separate “zones” in the flocculus and two halves, the caudal and rostral half.

Circuitry of the flocculus

The flocculus has a complex circuitry that is reflected in the structure of the zones and halves. These "zones" of the flocculus refer to five separate groupings of

Purkinje cells Purkinje cells or Purkinje neurons, named for Czech physiologist Jan Evangelista Purkyně who identified them in 1837, are a unique type of prominent, large neuron located in the cerebellar cortex of the brain. With their flask-shaped cell bo ...

that project to different areas of the brain. Depending upon where stimulus occurs in the flocculus, signals can be projected to very different parts of the brain. The first and third zones of the flocculus project to the superior vestibular nucleus, the second and fourth zones project to the medial vestibular nucleus, and the fifth zone projects to the interposed posterior nucleus, a part of the cerebellum. The anatomy of the flocculus shows that it is composed of two disjointed lobes or halves. The “halves” of the flocculus refer to the caudal half and the rostral half, and they indicate from where fiber projections are received and the path in which a signal travels. The caudal half of the flocculus receives mossy fiber projections mainly from the

vestibular system The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating motor coordination, movement with balance. Together with the cochlea, a part of the auditory sys ...

and tegmental pontine reticular nucleus, an area within the floor of the midbrain that affects the axonal projections or images received by the cerebellum. Vestibular inputs are also carried through climbing fibers that project into the flocculus, stimulating Purkinje cells. Leading research would suggest that climbing fibers play a specific role in motor learning. The climbing fibers then send the image or projection to the part of the brain that receives electrical signals and generates movement. From the midbrain, corticopontine fibers carry information from the primary motor cortex. From there, projections are sent to the

ipsilateral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

pontine nucleus in the ventral pons, both of which are associated with projections to the cerebellum. Finally, pontocerebellar projections carry vestibulo-occular signals to the contralateral cerebellum via the middle cerebellar peduncle. The rostral half of the flocculus also receives mossy fiber projections from the

pontine nuclei The pontine nuclei (or griseum pontis) are all the neurons of the ventral pons. Corticopontine fibres project from the primary motor cortex to the ipsilateral pontine nucleus; pontocerebellar fibers then relay the information to the contralater ...

; however, it receives very little projection from the vestibular system.

Function

The flocculus is a part of the vestibulo-ocular reflex system and is used to help stabilize gaze during head rotation about any axis of space. Neurons in both the vermis of cerebellum and flocculus transmit an eye velocity signal that correlates with

smooth pursuit In the scientific study of vision, smooth pursuit describes a type of eye movement in which the eyes remain fixated on a moving object. It is one of two ways that visual animals can voluntarily shift gaze, the other being saccadic eye movement ...

Flocculus role In learning basic motor functions

The idea that the flocculus is involved in motor learning gave rise to the “flocculus hypothesis.” This hypothesis argues that the flocculus plays a key role in the vestibulo-ocular system, most importantly the ability for the vestibular system to adapt to a shift in the visual field. The learning of basic

motor skills A motor skill is a function that involves specific movements of the body's muscles to perform a certain task. These tasks could include walking, running, or riding a bike. In order to perform this skill, the body's nervous system, muscles, and b ...

, including walking, balancing, and the ability to sit up, can be attributed to early patterns and pathways associated with the vestibulo-ocular reflex (VOR) and the pathways formed in the cerebellum that contribute to the learning of basic motor skills. The flocculus appears to be included in a VOR pathway that aids in the adaptation to a repeated shift in the visual field. A shift in the visual field affects an individual's spatial recognition. The leading research would suggest that the flocculus aids in the synchronization of eye and motor functions after a visual shift occurs in order for the visual field and the motor skills to function together. If this shift is repeated the flocculus essentially trains the brain to fully readjust to these repeated stimuli.

Location

Human brain midsagittal view description

Constituted by two disjointed-shaped lobes, the flocculus is positioned within the lowest level of the cerebellum. There are three main subdivisions in the cerebellum and the flocculus is contained within the most primitive the vestibulocerebellum. Its lobes are linked through a circuit of neurons connecting to the vermis, the medial structure in the cerebellum. Extensions leave the base of the follucular's lobes which then connect to the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

. The cerebellum, which houses the flocculus, is located in the back and at the base of the

human brain The human brain is the central organ (anatomy), organ of the nervous system, and with the spinal cord, comprises the central nervous system. It consists of the cerebrum, the brainstem and the cerebellum. The brain controls most of the activi ...

, directly above the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is conti ...

Clinical significance

The flocculus is most important for the pursuit of movements with the eyes. Lesions in the flocculus impair control of the vestibulo-ocular reflex, and gaze holding also known as

vestibulocerebellar syndrome Vestibulocerebellar syndrome, also known as vestibulocerebellar ataxia, is a progressive neurological disorder that causes a variety of medical problems. Initially symptoms present as periodic attacks of abnormal eye movements but may intensify t ...

. The deficits observed in patients with lesions to this area resemble dose-dependent effects of alcohol on pursuit movements. Bilateral lesions of the flocculus reduce the gain of

, which is the steady tracking of a moving object by the eyes. Instead, the bilateral lesions of the flocculus result in saccadic pursuit, in which smooth tracking is replaced by simultaneous rapid movements, or jerking motions, of the eye to follow an object toward the ipsilateral visual field. These lesions also impair the ability to hold the eyes in the eccentric position, resulting in gaze-evoked

nystagmus Nystagmus is a condition of involuntary (or voluntary, in some cases) Eye movement (sensory), eye movement. People can be born with it but more commonly acquire it in infancy or later in life. In many cases it may result in visual impairment, re ...

toward the affected side of the cerebellum. Nystagmus is the constant involuntary movements of the eyes; a patient can have either horizontal nystagmus (side-to-side eye movements), vertical nystagmus (up and down eye movements), or rotary nystagmus (circular eye movements). The flocculus also plays a role in keeping the body oriented in space. A lesion in this area will result in

ataxia Ataxia (from Greek α- negative prefix+ -τάξις rder= "lack of order") is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in e ...

, a neurological disorder that results in the deterioration of the coordination of muscle movements, and unsteady bodily movements such as swaying and staggering.

Associated conditions

The conditions and systems associated with floccular loss are considered to be a subset of a

vestibular The Vestibular (from , "entrance hall") is a competitive examination and is the primary and widespread entrance system used by Brazilian universities to select the students admitted. The Vestibular usually takes place from November to January, ...

disease A disease is a particular abnormal condition that adversely affects the structure or function (biology), function of all or part of an organism and is not immediately due to any external injury. Diseases are often known to be medical condi ...

. Some symptoms of common vestibular diseases include: head tilting, an inability to stand,

, dizziness, vomiting and

strabismus Strabismus is an eye disorder in which the eyes do not properly align with each other when looking at an object. The eye that is pointed at an object can alternate. The condition may be present occasionally or constantly. If present during a ...

. Because of the flocculus’ role in the vestibular system, the inner ear,

equilibrioception The sense of balance or equilibrioception is the perception of balance and spatial orientation. It helps prevent humans and nonhuman animals from falling over when standing or moving. Equilibrioception is the result of a number of sensory sy ...

, and both peripheral and central vision is affected by any loss or damage to the flocculus. These systems are affected because damage to the flocculus prevents any changes from being stored in regards to visual and motor communication, meaning that although the VOR is still intact these systems are unable to store changes in gain or eye movement as the head is rotated back and forth.

Additional images

File:Human cerebellum anterior view description.JPG, Human cerebellum anterior view File:Slide2SEER.JPG, Cerebellum. Inferior surface. File:Slide3EER.JPG, Cerebellum. Inferior surface. File:Slide4SER.JPG, Cerebellum. Inferior surface.

References

External links

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