What is the LGN?
It is a small, ovoid, ventral projection of the thalamus where the thalamus connects with the optic nerve. There are two LGNs, one on the left and another on the right side of the thalamus.
Where does the LGN receive its input from?
In addition to retinal afferents, the LGN receives input from multiple sources including striate cortex, the thalamic reticular nucleus (TRN), and the brainstem. The LGN therefore represents the first stage in the visual pathway at which cortical top-down feedback signals could affect information processing.
How many neurons are in the LGN?
Information Organization in LGN Bilateral structure with six layers 1 million neurons in total Each layer receives signal from one eye Layer 2,3,5 receives from ipsilateral eye Layer 1,4,6 receives from contralateral eye Each eye send half information to each side LGN Slide 5 Aditi Majumder, UCI Retinotopic Map Each location in LGN maps
Is the LGN in both hemispheres of the brain?
The LGN and the medial geniculate nucleus which deals with auditory information are both thalamic nuclei and so are present in both hemispheres . The LGN receives information directly from the ascending retinal ganglion cells via the optic tract and from the reticular activating system.
What does LGN of the brain do?
The lateral geniculate nucleus (LGN) belongs to the category of sensory projection nuclei of the thalamus and plays an essential role in normal visual processing.
Where is the lateral nucleus located?
the thalamusThe lateral geniculate nucleus is located within the lateral geniculate body, an ovoid projection of the posterior aspect of the thalamus. The lateral geniculate nucleus represents the thalamic relay station of the visual pathway.
What are the layers of the lateral geniculate nucleus?
The lateral geniculate nucleus exhibits a layered structure. There are two magnocellular layers, four parvocellular layers, and koniocellular layers between each of the magnocellular and parvocellular layers.
Is the LGN in the thalamus?
In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral projection of the thalamus where the thalamus connects with the optic nerve.
What part of the brain is the thalamus located?
diencephalonThe thalamus is a paired gray matter structure of the diencephalon located near the center of the brain. It is above the midbrain or mesencephalon, allowing for nerve fiber connections to the cerebral cortex in all directions — each thalamus connects to the other via the interthalamic adhesion.
Where does the LGN project to?
6.1. 1.3 Visual cortex. Neurons in the LGN project to striate cortex (also known as primary visual cortex or V1), an anatomically distinctive cortical region in the occipital lobe, at the back of the brain.
How many layers are in the LGN?
sixThe LGN consists of six eye-specific layers, four of which receive inputs from parvocellular retinal ganglion cells, and two of which receive magnocellular inputs. Each layer is organized into a precise retinotopic map.
What happens if the lateral geniculate nucleus is damaged?
Damage at site #4 and #5: damage to the optic tract (#4) or the fiber tract from the lateral geniculate to the cortex (#5) can cause identical visual loss. In this case, loss of vision of the right side. Partial damage to these fiber tracts can cause other predictable visual problems.
Which nucleus is the most lateral?
dentate nucleiThe cerebellar nuclei comprise 4 paired deep grey matter nuclei deep within the cerebellum near the fourth ventricle. They are arranged in the following order, from lateral to medial: dentate nuclei (the largest and most lateral)
What is located in the nucleus?
The nucleus (plural, nuclei) houses the cell's genetic material, or DNA, and is also the site of synthesis for ribosomes, the cellular machines that assemble proteins. Inside the nucleus, chromatin (DNA wrapped around proteins, described further below) is stored in a gel-like substance called nucleoplasm.
Why is the nucleus located in the center of the cell?
The nucleus is located toward the center of the cell because it controls all of the cell's movements, the cell's feeding schedule and the cell's reproduction. Its central location enables it to reach all parts of the cell easily.
Is nucleus always in the center of the cell?
The nucleus is not always in the center of the cell. It will be a big dark spot somewhere in the middle of all of the cytoplasm (cytosol). You probably won't find it near the edge of a cell because that might be a dangerous place for the nucleus to be.
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What is the LGN in the visual cortex?
The LGN is the thalamic stage in the retinocortical projection and has traditionally been viewed as a simple relay between the retina and the visual cortex ( Sherman and Guillery, 2001 ). The LGN consists of six eye-specific layers, four of which receive inputs from parvocellular retinal ganglion cells, and two of which receive magnocellular inputs. Each layer is organized into a precise retinotopic map. In addition to these retinal afferents, the LGN receives input from other sources including the primary visual cortex (V1), thalamic reticular nucleus (TRN), superior colliculus (SC), and brainstem. The functional role of these feedback inputs to the LGN is not well understood. Given its compact nature and retinotopic organization, the LGN would be an ideal stage in the processing hierarchy to efficiently modulate the sensory processing of information from specific and perhaps large portions of the visual field. Here, we review studies that used functional magnetic resonance imaging (fMRI) to investigate attentional response modulation in the human LGN ( O'Connor et al., 2002).
What inputs does the LGN receive?
In addition to these retinal afferents, the LGN receives input from other sources including the primary visual cortex (V1), thalamic reticular nucleus (TRN), superior colliculus (SC), and brainstem. The functional role of these feedback inputs to the LGN is not well understood.
What are the inputs to the DLG?
Cortical inputs to the DLG mainly derive from the primary visual cortex (area 17). The various cortical layers of the primary visual cortex have different projection patterns to the visual thalamus ( Bourassa and Deschênes, 1995). Fibers originating in the upper part of layer 6 project to the DLG and terminate in rostrocaudally oriented bands or “rods” that run parallel to the lines of projection of retinal afferents. Neurons in the deeper part of layer 6 project to the lateral part of the lateral posterior thalamic nucleus and give off collaterals to the DLG, where they participate in the formation of the rods. Neurons in layer 5 of the visual cortex send projections to the brainstem, with collaterals to the ventral lateral geniculate nucleus, lateral posterior nucleus, and lateral dorsal thalamic nucleus (Bourassa and Deschênes, 1995 ). Layer 6 corticothalamic fibers send collaterals to the reticular thalamic nucleus but layer 5 axons do not. The fibers terminating in DLG that originate from layer 6 have small “en passant” varicosities which at the ultrastructural level show characteristics of the RS-type boutons and may be considered “modulators” ( Jones, 1985, 2007; Bourassa and Deschênes, 1995; Price, 1995; Sherman and Guillery, 2001, 2006 ).
What is the DLG of rats?
The dorsal lateral geniculate nucleus (DLG) can be readily identified in Nissl-stained sections, in acetylcholinesterase-stained sections wherein the DLG shows moderate activity (Paxinos and Watson, 2014 ), and in serotonin stained tissue in which DLG shows very dense fiber labeling ( Vertes et al., 2010 ). The cytoarchitecture of the DLG of rats is rather homogeneous. The majority of dorsal lateral geniculate neurons are thalamocortical projection cells. Unlike most other principal thalamic nuclei of the rat, the DLG contains several types of interneurons, namely, GABAergic, NADPH diaphorase-containing neurons, and those co-expressing both substances ( Ohara et al., 1983; Jones, 1985, 2007; Gabbott and Bacon, 1994 ). In contrast to many other mammalian species, the rat DLG is not clearly laminated, although fiber bundles running in a ventrolateral to dorsomedial direction, parallel to the optic tract, impose a certain orientation on the neurons of the DLG. However, optic fibers from the ipsilateral and contralateral eyes in the caudolateral part of DLG remain segregated and create a “hidden lamination,” with the lateral “outer shell” of DLG receiving input from the contralateral eye. The medial part of DLG, called the “inner core,” consists of two regions: the most medial region receives input from the contralateral eye and the lateral region is innervated by the ipsilateral eye ( Jones, 1985, 2007; Reese, 1988 ). Calcium-binding proteins are differentially distributed in fibers and neurons of the dorsal lateral geniculate nucleus. Whereas calretinin and parvalbumin are present only in fibers, calbindin D28K is also expressed in (inter)neurons, in particular in the outer shell ( Luth et al., 1993; Paxinos et al., 1999 ). The plexus of calretinin fibers is most dense in the outer shell ( Paxinos et al., 1999 ). Parvalbumin fibers likely originate from the retina and the reticular thalamic nucleus, and calretinin fibers from the retina ( Arai et al., 1992; Luth et al., 1993 ). Calbindin D28K-containing fibers may be derived from the superior colliculus ( Lane et al., 1997 ).
What is the dorsal lateral geniculate nucleus?
The dorsal lateral geniculate nucleus (DLG) receives input from the retina and projects to the visual cortex. This nucleus has been intensively studied in the cat and monkey, but with the advent of gene targeting technology, increasing attention is being paid to the DLG of the mouse. The DLG is the only thalamic nucleus in the mouse that contains both glutamatergic (excitatory) cells and GABAergic (inhibitory) cells. Other thalamic sensory nuclei in the mouse do not contain GABAergic interneurons (Arcelli et al., 1997 ). In primates, all thalamic projection nuclei contain both glutamatergic and GABAergic neurons.
What is the DLG?
The DLG forms the main relay between the retina and the primary visual cortex (area 17 or V1), the optic terminations in the dorsal lateral geniculate nucleus being retinotopically organized (see above; Jones, 1985; Reese, 1988).
What type of axons are used in DLG?
All the fast-conducting optic axons (with Y-like properties) appear to project to the DLG ( Dreher et al., 1985a; Sefton, 1968 ). In turn, relay cells receiving fast inputs have fast-conducting axons projecting to occipital cortical areas ( Hale et al., 1979; Noda and Iwama, 1967 ). About 2000–4000 type I retinal ganglion cells, which are the presumed counterparts of Y-like cells ( Dreher et al., 1985a; Peichl, 1989 ), project to DLG. Cells with Y-like properties represent 27% ( Hale et al., 1979) to 48% (calculated from Fukuda et al., 1979) of all neurons recorded in DLG. Sampling bias of the electrode does not seem to be an important factor in DLG of the cat ( Friedlander et al., 1981 ). If this assumption is valid for the rat, a single incoming Y-like optic axon is likely to diverge to innervate a minimum of about one, and possibly up to four, relay cells in DLG. Indeed, an even larger amplification is observed for the Y system in DLG of the cat ( Friedlander et al., 1981 ). Because each 2a (presumed Y-like) axon has on average 23 terminals ( Brauer et al., 1975 ), between 6 and 23 2a terminals would excite a fast-conducting relay cell in DLG.
What is the role of LGN in blindness?
For individuals diagnosed with blindsight due to a lesion of the primary visual cortex, the LGN plays an essential role in mediating visually relevant information that is below the level of conscious awareness. [1]
What is the lateral geniculate nucleus?
The lateral geniculate nucleus is among the numerous thalamic nuclei that show substantial alterations in individuals with spinocerebellar ataxia type 2 (and possibly type 3), including astrocytosis, loss of neuronal bodies, and increased levels of lipofuscin. [31][32]
How early can a lateral geniculate nucleus be formed?
Early development of the lateral geniculate nucleus characteristically demonstrates heightened retinogeniculate synaptogenesis (as early as 13 weeks of gestation) followed by the subsequent development of corticogeniculate connectivity. However, the structural development of retinogeniculate projections (without synapse formation) occurs as early as 7 weeks.[17] A critical period of increased cell metabolism and synapse development occurs at 15 to 20 weeks.[18] By the end of this period, retinogeniculate projections to the LGN have developed eye-specific segregation.[19] The development of the LGN’s laminar structure occurs at approximately 22 to 25 weeks, beginning with the ventral aspect (the magnocellular layers).[20] The later lamination of the LGN suggests that this process is a function of retinal activity. This concept receives further support from the finding in animal studies that interrupting retinogeniculate segregation severely disrupts the development of LGN's laminar organization. [21]
What are the different types of cells in the lateral geniculate nucleus?
The basis of the structure of the lateral geniculate nucleus is mostly in terms of its three distinct cell types: magnocellular (M), parvocellular (P), and koniocellular (K). P and M cells are arranged in six different layers (four dorsal P layers and two ventral M layers), with retinal ganglion signals from the ipsilateral eye synapsing on layers 2, 3, and 5, and signals from the contralateral eye synapsing on layers 1, 4, and 6. M cells in the LGN receive input from the large-field, motion-sensitive Y-type retinal ganglion cells, while P cells receive input from the small-field, color-sensitive X-type retinal ganglion cells. Koniocellular cells project into regions ventral to each of the P and M laminae.
What is the extracellular matrix of the lateral geniculate nucleus?
The extracellular matrix of the lateral geniculate nucleus is characterized by a decreased presence of the traditional aggrecan-based matrix phenotype, perineuronal nets. It instead displays a high density of axonal coats, a related structure with a more localized matrix at dendrites, suggesting a different organizational strategy possibly specialized for rapid sensory processing. [6][7]
Which artery supplies the lateral geniculate nucleus?
The posterior cerebral artery supplies the lateral geniculate nucleus from the lateral posterior choroidal branch and by the internal carotid artery from its anterior choroidal branch. [22]
How does structural variation occur in the lateral geniculate nucleus?
Structural variation in the lateral geniculate nucleus can occur via divergent development of or subsequent damage to upstream structures in the visual pathway. Strabismic amblyopia, the permanent reduction of visual acuity due to abnormal development in the eyes’ alignment, is associated with a significant decrease in LGN gray matter density despite normal development other major neural regions in the visual pathway.[24] Damage to the optic nerve due to primary open-angle glaucoma can similarly induce atrophy in the LGN commensurate with the degree of condition severity. [25][26]Some animal research also suggests that a lack of input from the visual cortical regions can induce cell death sharing many features of apoptosis. [27]
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