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 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 zone projects to the medial vestibular nucleus, and the fifth zone projects to the interposed posterior nucleus, a part of the cerebellum.
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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 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.
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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. 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 smooth pursuit, which is the steady tracking of a moving object by the eyes.
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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.
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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. As a part of the cerebellum, the flocculus plays a part of 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.
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The flocculus appears to be included a VOR pathway that aids in the adaptation to a repeated shift in the visual field. A shift in the visual field affects an individuals spatial recognition. The leading research would suggest that 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 this repeated stimuli.
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4th ed. Sunderland, MA: Sinauer, 2008. Vestibulocerebellar syndrome has been categorized as an autosomal dominant neurological disorder although the specific effect on the vestibulocerebellum is unknown. It is possible that inheritance causes abnormalities in either the flocculus or in structures that project into the flocculus to maintain stability of the retinal image of stationary or moving visual objects.
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The cerebellum, which houses the flocculus, is located in the back and at the base of the human brain, directly above the brainstem.
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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, including walking, balancing, and the ability to sit up, can be attributed to early patterns and pathways associated with the vestibulo-occular reflex and the pathways formed in the cerebellum. Within the cerebellum pathways that contribute to the learning of basic motor skills.
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The conditions and systems associated with floccular loss are considered to be a subset of a vestibular disease. Some symptoms of common vestibular diseases include: head tilting, an inability to stand, ataxia, dizziness, vomiting and strabismus. Because of the flocculus’ role in the vestibular system, the inner ear, equilibrioception, 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 you rotate your head back and forth.
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10:Flocculonodular lobeConstituted 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.
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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.
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The flocculus (Latin: tuft of wool, diminutive) is a small lobe of the cerebellum 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, and aids in the learning of basic motor skills in the brain. It is associated with the nodulus of the vermis; together, these two structures compose the vestibular part of the cerebellum.
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There is currently no cure for vestibulocerebellar syndrome, although some drug therapies have been effective in alleviating particular symptoms of the disorder. Anterior view of the cerebellum showing the flocculus and nodulus of the vestibulocerebellum.
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The anterior inferior cerebellar artery (AICA) is the principal vessel of the cerebellopontine angle. It also contains two cranial nerves – the vestibulocochlear nerve and the facial nerve; the cerebellar flocculus and the lateral recess of the fourth ventricle.
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The amount of tissue supplied by the AICA is variable, depending upon whether the PICA is more or less dominant, but usually includes the anteroinferior surface of the cerebellum, the flocculus, middle cerebellar peduncle and inferolateral portion of the pons.
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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; however, it receives very little projection from the vestibular system.
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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 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.
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The flocculus sends out neural signals that produce small, automatic movements in the eye muscles. These keep the image on an animal's retina steady. Pterosaurs may have had such a large flocculus because of their large wing size, which would mean that there was a great deal more sensory information to process. The low relative mass of the flocculi in birds is also a result of birds having a much larger brain overall; though this has been considered an indication that pterosaurs lived in a structurally simpler environment or had less complex behaviour compared to birds, recent studies of crocodilians and other reptiles show that it is common for sauropsids to achieve high intelligence levels with small brains.
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Head and neck of specimen FMNH PR 2836 Computed tomography, also known as CT scanning, of a complete Majungasaurus skull (FMNH PR 2100) allowed a rough reconstruction of its brain and inner ear structure. Overall, the brain was very small relative to body size, but otherwise similar to many other non- coelurosaurian theropods, with a very conservative form closer to modern crocodilians than to birds. One difference between Majungasaurus and other theropods was its smaller flocculus, a region of the cerebellum that helps to coordinate movements of the eye with movements of the head. This suggests that Majungasaurus and other abelisaurids like Indosaurus, which also had a small flocculus, did not rely on quick head movements to sight and capture prey.
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The flocculonodular lobe (vestibulocerebellum) is a lobe of the cerebellum consisting of the nodule and the flocculus. The two flocculi are connected to the midline structure called the nodulus by thin pedicles. It is placed on the anteroinferior surface of cerebellum. This region of the cerebellum has important connections to the vestibular nuclei and uses information about head movement to influence eye movement.
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The flocculus is relatively large on most ankylosaurids. Another neuroanatomical character is the elongated lagena, which is prominent in Euoplocephalus, Tarchia and Talarurus. This anatomical feature indicates that ankylosaurids had a large range of sound perception, specially for low frequencies. In addition to these findings, the preserved rostrum in MPC-D 100/1354 is broad, almost rectangular in shape and somewhat stocky.
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CT scan of the holotype showing endocast and endosseous labyrinth In 2020, German paleontologist Marco Schade and colleagues analyzed the anatomy of the holotype skull braincase through CT scans, revealing numerous details about behavioral capabilities of Irritator. With the scans, they created a 3D model of the skull and braincase, discovering that Irritator had elongated olfactory tracts and a relatively large floccular recesses (area that pierces through the semicircular canals and connects the brain with the inner ear). The flocculus itself, is an important element in the coordination and control of head and ocular movements during gaze stabilization (visual ability during head movement), by being involved in the coordination of the vestibulo-ocular (VOR) and vestibulo- collic (VCR) reflexes. The flocculus appears to be enlarged in taxa that rely on quick movements of the head body.
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Pathological symptoms of the disorder may appear within the first 1–2 years of life although time of onset varies greatly among patients. The severity of symptoms typically progresses with age. The exact cause of the disorder and its pathogenic effect on the flocculus is unknown. A single genetic locus, however, critical in early eye movement control pathways on chromosome 13q31-q33 has been discovered.
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The mechanism of the vestibulo-ocular reflex. Vestibulocerebellar syndrome is caused by a failure in the function of the flocculus of the vestibulocerebellum, one of the three main divisions of the cerebellum. Generally, the cerebellum is responsible for regulating motor commands. The main function of the vestibulocerebellum is to receive sensory input from the vestibular nuclei in the brainstem and to regulate equilibrium, balance, and the vestibulo-ocular reflex accordingly.
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An X-ray study of pterosaur brain cavities revealed that the animals (Rhamphorhynchus muensteri and Anhanguera santanae) had massive flocculi. The flocculus is a brain region that integrates signals from joints, muscles, skin and balance organs. The pterosaurs' flocculi occupied 7.5% of the animals' total brain mass, more than in any other vertebrate. Birds have unusually large flocculi compared with other animals, but these only occupy between 1 and 2% of total brain mass.
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The biventer lobule (or biventral lobule) is a region of the cerebellum. It is triangular in shape; its apex points backward, and is joined by the gray band to the pyramid. The lateral border is separated from the inferior semilunar lobule by the postpyramidal fissure. The base is directed forward, and is on a line with the anterior border of the tonsil, and is separated from the flocculus by the postnodular fissure.
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However, Aucasaurus exhibits a floccular process that is relatively larger than that of Majungasaurus. In Aucasaurus the flocculus is enclosed in an 8-shaped floccular recess, similar in shape and size to that observed in Abelisaurus, suggesting that the two Patagonian taxa were capable of a slightly wider range of movements of the head. The labyrinth of the inner ear is similar in shape and size to the semicircular canals of Majungasaurus, although the lateral semicircular canal is shorter in Aucasaurus.
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UBCs are plentiful in those regions linked to vestibular functions. In mammals, UBCs show an uneven distribution within the granule cell domains of the hindbrain, being the most dense in the vermis, part of the flocculus/paraflocculus complex, and layers 2–4 of the dorsal cochlear nucleus. In the rat cerebellum, UBCs outnumber Golgi cells by a factor of 3 and approximately equal the number of Purkinje cells. Like other glutamatergic cells of the cerebellum, UBCs originate in the rhombic lip.
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Fossil specimen, National Museum of Natural Science Braincase scans indicate that Dilong had an S-shaped brain protected by thin meninges, unlike Tyrannosaurus which has a more linear brain protected by thicker meninges; this is probably a size-related trait, as it is in crocodilians. The large flocculus of Dilong suggests it was agile and had good balance, while small olfactory tracts suggest that its sense of smell was not as refined as that of Tyrannosaurus and other more advanced tyrannosauroids.
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The nodule (nodular lobe), or anterior end of the inferior vermis, abuts against the roof of the fourth ventricle, and can only be distinctly seen after the cerebellum has been separated from the medulla oblongata and pons. On either side of the nodule is a thin layer of white substance, named the posterior medullary velum. It is semilunar in form, its convex border being continuous with the white substance of the cerebellum; it extends on either side as far as the flocculus.
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From the anterior portion of the medulla oblongata, the glossopharyngeal nerve passes laterally across or below the flocculus, and leaves the skull through the central part of the jugular foramen. From the superior and inferior ganglia in jugular foramen, it has its own sheath of dura mater. The inferior ganglion on the inferior surface of petrous part of temporal is related with a triangular depression into which the aqueduct of cochlea opens. On the inferior side, the glossopharyngeal nerve is lateral and anterior to the vagus nerve and accessory nerve.
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Behind the jugal is the quadratojugal, which has traditionally been depicted as hypertrophied and occupying the location of the back portion of the jugal; it is actually a small, half moon-shaped bone wedged between the jugal and the quadrate and situated below the elongate infratemporal fenestra. Overall, the infratemporal fenestra is shaped similarly to the eye socket. The quadrates are strap-like, and wrap around from the back to the bottom of the skull. Although mostly obscured, the removal of the parietal during preparation has exposed part of the endocast of the brain, which has a large flocculus and cerebrum.
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The 2007 specimen skulls have brought new insights into the neurocranial capacities and dietary habits of Talarurus, specifically the specimen MPC-D 100/1354, which is a well-preserved, almost complete cranium. MPC-D 100/1354 was described in extensive detail along with a very complete skull of Tarchia by Paulina-Carabajal et al. 2017, they noted that ankylosaurids had well- developed gaze stabilization and auditive senses, differing from nodosaurids, by examining the endocranial region of the selected specimens. The presence of the flocculus was first reported in Talarurus by Maryańska and later in other related ankylosaurids, however, this lobe seems to be absent or reduced in nodosaurids.
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The ascending MLF mainly arises from the superior and medial vestibular nucleus (VN) and is involved in the generation of the vestibulo-ocular reflex (VOR). This is achieved by inputs to the VN from: # the vestibulocochlear (8th cranial) nerve about head movements, # gait adjustments from the flocculus of the cerebellum, # head and neck proprioceptors and foot and ankle muscle spindle, via the fastigial nucleus. Descending fibers can also arise from the superior colliculus in the rostral midbrain for visual reflexes, the accessory occulomotor nuclei in the rostral midbrain for visual tracking, and the pontine reticular formation, which facilitates extensor muscle tone. Ascending tracts arise from the vestibular nucleus (VN) and terminate in the III, IV and VI nuclei, which are important for visual tracking.
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It is also possible that the pit is an opening for the pineal gland, as it is in approximately the right position, but this is less likely because no other archosauriforms have such an opening, and the opening does not appear to be connected to any internal structures. The pit has the same texture as the bosses, suggesting that it was also potentially covered in keratin. The eye socket is very large, and it is surrounded by mineralized cartilage, a trait only seen otherwise in pachycephalosaurs. CT scans also revealed large optic nerves as well as long semicircular canals and a relatively large cerebellar flocculus (both involved in stabilizing gaze, although long semicircular canals are also associated with bipedal stances).
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Endocast of the brain As demonstrated by a CT scan, the braincase of Allkaruen exhibits a unique set of traits that are intermediate between more basal pterosaurs such as Rhamphorhynchus and more derived pterodactyloid pterosaurs such as Anhanguera. These traits are the position of the anterior semicircular canal of the inner ear, the relative orientations of the occiput and occipital condyle, the relative positions of the lateral margins of the flocculus and cerebral hemispheres, and the ratio between the length of the brain and the height of the hindbrain. In addition, the relative orientations of the frontal bone and lateral semicircular canal are more similar to Rhamphorhynchus than Anhanguera, while the optic lobes are positioned lower than the forebrain as in pterodactyloids. This unique combination of characters indicates that the anatomy of the braincase in pterodactyloids evolved through mosaic evolution.
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The flocculus, a lobe of the cerebellum, is proportionally large, and is related to the vestibulo–ocular reflex (stablise gaze while moving the head). Judging by the orientation of the semi-circular canals in the ear (which have to be oriented parallel to the ground), the head of the gorgonopsian specimen GPIT/RE/7124 would have tilted forward by about 41°, increasing the overlap between the visual fields of the 2 eyes and improving binocular vision useful to a predator. Unlike either reptiles or mammals, the semi-circular canals are flat, probably because it was wedged between the opisthotic (an inner ear bone) and supraoccipital bones. Like other Permian therapsids, gorgonopsians had developed several mammalian characteristics, including a parasagittal gait (the limbs were vertically oriented and moved parallel to the spine) as opposed to the sprawling gait of amphibians and earlier synapsids, a consequential reduction in tail size and phalangeal formula (the number of joints per digit, which was 2.3.4.5.
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