geniculate body

膝状体

関

geniculate、lateral geniculate body、medial geniculate body

WordNet

1. invest with or as with a body; give body to (同)personify
2. the external structure of a vehicle; "the body of the car was badly rusted"
3. the main mass of a thing
4. a natural object consisting of a dead animal or person; "they found the body in the lake" (同)dead body
5. the entire structure of an organism (an animal, plant, or human being); "he felt as if his whole body were on fire" (同)organic structure, physical structure
6. a collection of particulars considered as a system; "a body of law"; "a body of doctrine"; "a body of precedents"
7. a group of persons associated by some common tie or occupation and regarded as an entity; "the whole body filed out of the auditorium"; "the student body"; "administrative body"
8. an individual 3-dimensional object that has mass and that is distinguishable from other objects; "heavenly body"
9. the central message of a communication; "the body of the message was short"
10. bent at a sharp angle

PrepTutorEJDIC

1. 〈C〉『身体』,肉体 / 〈C〉(人・動物の)『胴体』 / 〈C〉)物の)『主要部』,本体《+『of』+『名』》 / 〈C〉(…の)『団体』,群れ:(…のたくさんの)集まり《+『of』+『名』》 / 〈C〉物体,…体 / 〈U〉実質;(酒・味などの)こく / 〈C〉《話》人
2. 《英話》人;(特に)男

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/02/26 19:47:52」(JST)

wiki en

[Wiki en表示]

Brain: Lateral geniculate nucleus
Hind- and mid-brains; postero-lateral view. (Lateral geniculate body visible near top.)
Latin	Corpus geniculatum laterale
Part of	Thalamus
System	Visual
Artery	Anterior choroidal and Posterior cerebral
Vein	Terminal vein
NeuroNames	hier-335
NeuroLex ID	birnlex_1662

The lateral geniculate nucleus (LGN) is the primary relay center for visual information received from the retina of the eye. The LGN is found inside the thalamus of the brain.

The LGN receives information directly from the ascending retinal ganglion cells via the optic tract and from the reticular activating system. Neurons of the LGN send their axons through the optic radiation, a direct pathway to the primary visual cortex. In addition, the LGN receives many strong feedback connections from the primary visual cortex. In mammals, including humans, the two strongest pathways linking the eye to the brain are those projecting to the LGNd (dorsal part of the LGN in the thalamus), and to the superior colliculus (SC).

Structure

Both the left and right hemisphere of the brain have a lateral geniculate nucleus, named so for its resemblance to a bent knee (genu is Latin for "knee"). In many primates, including humans and macaques, it has layers of cell bodies with layers of neuropil in between, in an arrangement something like a club sandwich or layer cake, with cell bodies of LGN neurons as the "cake" and neuropil as the "icing". In humans and macaques the LGN is normally described as having six distinctive layers. The inner two layers, 1 and 2, are called the magnocellular layers, while the outer four layers, 3, 4, 5, and 6, are called parvocellular layers. An additional set of neurons, known as the koniocellular sublayers, are found ventral to each of the magnocellular and parvocellular layers. This layering is variable between primate species, and extra leafleting is variable within species.

M, P, K cells

Type	Size*	Source / Type of Information	Location	Response	Number
M: Magnocellular cells	Large	Rods; necessary for the perception of movement, depth, and small differences in brightness	Layers 1 and 2	rapid and transient	?
P: Parvocellular cells (or "parvicellular")	Small	Cones; long- and medium-wavelength ("red" and "green" cones); necessary for the perception of color and form (fine details).	Layers 3, 4, 5 and 6	slow and sustained	?
K: Koniocellular cells (or "interlaminar")	Very small cell bodies	Short-wavelength "blue" cones.	Between each of the M and P layers

Schematic diagram of the primate LGN. Layers 1 and 2 are more ventrally located, and are next to the incoming optic tract fibers.

• Size relates to cell body, dendritic tree and receptive field

The magnocellular, parvocellular, and koniocellular layers of the LGN correspond with the similarly named types of ganglion cells.

Koniocellular cells are functionally and neurochemically distinct from M and P cells and provide a third channel to the visual cortex. They project their axons between the layers of the lateral geniculate nucleus where M and P cells project. Their role in visual perception is presently unclear; however, the koniocellular system has been linked with the integration of somatosensory system-proprioceptive information with visual perception, and it may also be involved in color perception.^{[citation needed]}

The parvo- and magnocellular fibers were previously thought to dominate the Ungerleider–Mishkin ventral stream and dorsal stream, respectively. However, new evidence has accumulated showing that the two streams appear to feed on a more even mixture of different types of nerve fibers.

The other major retino–cortical visual pathway is the tectopulvinar pathway, routing primarily through the superior colliculus and thalamic pulvinar nucleus onto posterior parietal cortex and visual area MT.

Ipsilateral and contralateral layers

Both the LGN in the right hemisphere and the LGN in the left hemisphere receive input from each eye. However, each LGN only receives information from one half of the visual field. This occurs due to axons of the ganglion cells from the inner halves of the retina (the nasal sides) decussating (crossing to the other side of the brain) through the optic chiasm (khiasma means "cross"). The axons of the ganglion cells from the outer half of the retina (the temporal sides) remain on the same side of the brain. Therefore, the right hemisphere receives visual information from the left visual field, and the left hemisphere receives visual information from the right visual field. Within one LGN, the visual information is divided among the various layers as follows:

• the eye on the same side (the ipsilateral eye) sends information to layers 2, 3 and 5
• the eye on the opposite side (the contralateral eye) sends information to layers 1, 4 and 6.

A simple mnemonic for remembering this is "See I? I see, I see," with "see" representing the C in "contralateral," and "I" representing the I in "ipsilateral."

Another way of remembering this is 2+3=5, which is correct, so ipsilateral side, and 1+4 doesn't equal 6, so contralateral.

This description applies to the LGN of many primates, but not all. The sequence of layers receiving information from the ipsilateral and contralateral (opposite side of the head) eyes is different in the tarsier. Some neuroscientists suggested that "this apparent difference distinguishes tarsiers from all other primates, reinforcing the view that they arose in an early, independent line of primate evolution".

In visual perception, the right eye gets information from the right side of the world (the right visual field), as well as the left side of the world (the left visual field). You can confirm this by covering your left eye: the right eye still sees to your left and right, although on the left side your field of view may be partially blocked by your nose.

In the LGN, the corresponding information from the right and left eyes is "stacked" so that a toothpick driven through the club sandwich of layers 1 through 6 would hit the same point in visual space six different times.

LGN inputs

The LGN receives input from retina.

At least in some species, the LGN also receives some inputs from the optic tectum (also known as the superior colliculus).

LGN output

Information leaving the LGN travels out on the optic radiations, which form part of the retrolenticular limb of the internal capsule.

The axons that leave the LGN go to V1 visual cortex. Both the magnocellular layers 1–2 and the parvocellular layers 3–6 send their axons to layer 4 in V1. Within layer 4 of V1, layer 4cβ receives parvocellular input, and layer 4cα receives magnocellular input. However, the koniocellular layers (in between layers 1–6) send their axons to layers 4a in V1. Axons from layer 6 of visual cortex send information back to the LGN.

Studies involving blindsight have suggested that projections from the LGN not only travel to the primary visual cortex but also to higher cortical areas V2 and V3. Patients with blindsight are phenomenally blind in certain areas of the visual field corresponding to a contralateral lesion in primary visual cortex; however, these patients are able to perform certain motor tasks accurately in their blind field, such as grasping. This suggests that neurons travel from the LGN to both the visual cortex and higher cortex regions.

Function in visual perception

The functions of the LGN are multiple. Its unique folding contributes to its utility by performing a range of anatomical calculations without requiring mathematical computations. These include both temporal correlations/decorrelations as well as spatial correlations. The resulting outputs include time correlated and spatially correlated signals resulting from summing the signals received from the left and right semifields of view captured by each of the two eyes. These signals are correlated in order to achieve a three-dimensional representation of object space as well as obtain information for controlling the precision (previously auxiliary) optical system (POS) of the visual modality.

The outputs serve several functions.

• A signal is provided to control the vergence of the two eyes so they converge at the principle plane of interest in object space.

• A signal is provided to control the focus of the eyes based on the calculated distance to the principle plane of interest.

• Computations are achieved to determine the position of every major element in object space relative to the principle plane. Through subsequent motion of the eyes, a larger stereoscopic mapping of the visual field is achieved.
  • A tag is provided for each major element in the central 1.2 degree field of view of object space. The accumulated tags are attached to the features in the merged visual fields forwarded to area 17 of the cerebral cortex (often described as the "primary" visual cortex or V1)
  • A tag is also provided for each major element in the visual field describing the velocity of the major elements based on its change in coordinates with time.
  • The velocity tags (particularly those associated with the peripheral field of view) are also used to determine the direction the organism is moving relative to object space.

These position and velocity tags are extracted prior to the information reaching area 17. They costitute the major source of information reported in blindsight experiments where an individual reports motion in a portion of the visual field associated with one hemisphere of area 17 that has been damaged by laceration, stroke, etc.

The output signals from the LGN determine the spatial dimensions of the stereoscopic and monoscopic portions of the horopter of the visual system.

It has been shown that while the retina accomplishes spatial decorrelation through center surround inhibition, the LGN accomplishes temporal decorrelation. This spatial–temporal decorrelation makes for much more efficient coding. However, there is almost certainly much more going on.

Like other areas of the thalamus, particularly other relay nuclei, the LGN likely helps the visual system focus its attention on the most important information. That is, if you hear a sound slightly to your left, the auditory system likely "tells" the visual system, through the LGN via its surrounding peri-reticular nucleus, to direct visual attention to that part of space. The LGN is also a station that refines certain receptive fields. Experiments using fMRI in humans reported in 2010 that both spatial attention and saccadic eye movements can modulate activity in the LGN.

Additional images

• Thalamus

• Dissection of brain-stem. Lateral view.

• Scheme showing central connections of the optic nerves and optic tracts.

• Thalamic nuclei

• 3D schematic representation of optic tracts

References

External links

• Malpeli J. Malpeli Lab Home Page. Retrieved September 1, 2004.
• BrainMaps at UCDavis lateral%20geniculate%20nucleus

• Atlas of anatomy at UMich eye_38—"The Visual Pathway from Below"
• BrainMaps at UCDavis lgn

• Mnemonic at medicalmnemonics.com 307 640

See also

• Medial geniculate nucleus—MGN processes auditory information

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Japanese Journal

• 右前脈絡叢動脈領域梗塞により左半側空間無視，構成障害および漢字失書を呈した1 例

• 安藤 喜仁,菱田 良平,橋本 律夫,中野 今治
• 脳卒中 36(2), 76-81, 2014
• 要旨：症例は67 歳右利き男性．右前脈絡叢動脈閉塞により外側膝状体近傍に限局した脳梗塞が生じ，左同名半盲，左半側空間無視と構成障害，漢字に強い失書を呈した．失語はみられなかった．過去に外側膝状体を中心とした病巣で半側空間無視が出現した報告は少なく，さらに構成障害と失書も合併したものは1 例のみであった．また，いずれの既報告例においても外側膝状体病変に加えて視床や後頭葉などを含む広範な部位に病変が認 …
• NAID 130004873607

• Localized Infarction of the Lateral Geniculate Body

• ,
• Internal Medicine 53(16), 1891-1892, 2014
• NAID 130004678423

• ラット聴皮質と視床における誘発電位と活動電位の3次元同時記録

• 高橋 和佐,白松(磯口) 知世,野田 貴大 [他]
• 聴覚研究会資料 = Proceedings of the auditory research meeting 43(8), 645-650, 2013-11-28
• NAID 40019903608

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Related Pictures

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★リンクテーブル★

リンク元	「膝状体」
拡張検索	「lateral geniculate body」
関連記事	「body」「geniculate」

「膝状体」

　　[★]

英

geniculate body、geniculate

関

外側膝状体、内側膝状体

「lateral geniculate body」

　　[★] 外側膝状体

同

LGB

同

外側膝状体

「body」

　　[★]

• n.

• 体、本体、身体、ボディー

「geniculate」

　　[★]

• adj.

• 膝状体の

関

geniculate body