Magnocellular cell

Last updated
Magnocellular cell
Details
System Visual system
Location Lateral geniculate nucleus of the thalamus
Identifiers
NeuroLex ID nifext_42
Anatomical terms of neuroanatomy

Magnocellular cells, also called M-cells, are neurons located within the magnocellular layer of the lateral geniculate nucleus of the thalamus. The cells are part of the visual system. They are termed "magnocellular" since they are characterized by their relatively large size compared to parvocellular cells.

Contents

Structure

Schematic diagram of the primate LGN. Lateral geniculate nucleus.png
Schematic diagram of the primate LGN.

The full details of the flow of signaling from the eye to the visual cortex of the brain that result in the experience of vision are incompletely understood. Many aspects are subject to active controversy and the disruption of new evidence. [1] [2]

In the visual system, signals mostly travel from the retina to the lateral geniculate nucleus (LGN) and then to the visual cortex. In humans the LGN is normally described as having six distinctive layers. The inner two layers, (1 and 2) are magnocellular cell (M cell) layers, while the outer four layers, (3,4,5 and 6), are parvocellular cell (P cell) layers. An additional set of neurons, known as the koniocellular cell (K cell) layers, are found ventral to each of the M cell and P cell layers. [2] [3] : 227ff  [4] These layers were named this way because cells in the M layers of the LGN are larger than cells in the P layers. [3] : 228  [5]

M cells in the LGN receive input from parasol ganglion cells (which some neuroscientists call M cells), [3] : 226  and P cells receive input from midget retinal ganglion cells (which some neuroscientists call P cells). [3] : 226  [6] [7]

Visual representation of the parvocellular and magnocellular pathways Magno Parvocellular Pathways.svg
Visual representation of the parvocellular and magnocellular pathways

From the LGN, the M pathway continues by sending information to the interblob regions of the 4Cα layer of the V1 region of the visual cortex, also called the "striate cortex". [6] Other cells in the striate are more influenced from signaling from P cells and yet others from K cells. As signals are passed to other regions of the cortex, the signals start to be less separate, more integrated, and more influenced by signals from other parts of the brain. While classically it is said that signaling through the M pathway ultimately flow out of the visual cortex through the dorsal stream and signaling through the P pathway ultimately flows to the ventral stream, subsequent studies have shown that both pathways influence both streams. [3] : 236 

Human visual pathway Human visual pathway.svg
Human visual pathway

Function

The magnocellular pathway cannot provide finely detailed or colored information, but still provides useful static, depth, and motion information. [8] [9] The M pathway has high light/dark contrast detection, [10] and is more sensitive at low spatial frequencies than high spatial frequencies. Due to this contrast information, M cells are essential for detecting changes in luminance, and performing visual search tasks and detecting edges. [11]

The M pathway is also important for providing information about the location of objects. M cells can detect the orientation and position of objects in space, [12] information that is sent through the dorsal stream. [13] This information is also useful for detecting the difference in positions of objects on the retina of each eye, an important tool in binocular depth perception. [14]

Cells in the M pathway have the ability to detect high temporal frequencies and can thus detect quick changes in the position of an object. [7] This is the basis for detecting motion. [10] [15] The information sent to the intraparietal sulcus (IPS) of the posterior parietal cortex allows the M pathway to direct attention and guide saccadic eye movements to follow important moving objects in the visual field. [8] [16] [17] In addition to following objects with the eyes, the IPS sends information to parts of the frontal lobe that allows the hands and arms to adjust their movements to correctly grasp objects based on their size, position, and location. [13] This ability has led some neuroscientists to hypothesize that the purpose of the M pathway is not to detect spatial locations, but to guide actions related to the position and motion of objects. [18]

Some information has also been found to support the hypothesis that the M pathway is necessary for facial processing. [19]

Clinical significance

Abnormal magnocellular pathways and magnocellular cells can be associated with various disorders and ocular impairments, including dyslexia, prosopagnosia and schizophrenia. [8] [15] [19]

Dyslexia

Dyslexia is a disability which affects individual’s ability to read. It often first manifests in childhood, if at all; however, dyslexia can manifest itself in adulthood because of a brain tumor or lesion on/penetrating M cells. [15] There is no clear idea of the role of M cells and the magnocellular pathway in dyslexia.

One theory suggests that the nonlinearity, size, and compensation of miniature eye movements of M cells all help to focus on a single target and blur the surroundings, which is crucial in reading. This suggests that M cells are underdeveloped in many dyslexics. This may be due to genetics, autoimmunity, or nutrition. The KIAA0319 gene on chromosome six controls cell migration to the LGN during development; and studies in transgenic mice and on brains of people with dyslexia examined after they died, show malformations in the LGN and cells expressing KIAA0319 growing in the wrong place. [8] M cells are vulnerable to antineuronal antibodies which attack and render them unusable in the magnocellular pathway. This could be a cause of why dyslexics are more likely to have weakened immune systems. [8]

Another line of research suggests that defective eye movement caused by M cells is the cause of dyslexia. Since the magnocellular system is sensitive to image movement, and dyslexia is posited to be caused by abnormalities in M cells, dyslexics tend to focus on words longer, take shorter scans when reading, and stop more often per line. The study postulates that this is not caused by dyslexia but rather, low comprehension of the text causing abnormal eye movements in M cells. Therefore, it is difficult to conclude the importance of M cells in dyslexia from this study. [15]

Schizophrenia

Schizophrenia is a mental disorder in which people are unable to differentiate what is real and what is not. It is believed that the magnocellular pathway may help with facial recognition and discrimination in children, but when this pathway is not developed completely or correctly, facial processing is more difficult for individuals later in life. This is seen in people with schizophrenia and occurs when there are issues in the integration of information from the M cell and P cell pathways, making it difficult for individuals with schizophrenia to differentiate between reality and hallucinations. [19]

Related Research Articles

<span class="mw-page-title-main">Visual cortex</span> Region of the brain that processes visual information

The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and then reaches the visual cortex. The area of the visual cortex that receives the sensory input from the lateral geniculate nucleus is the primary visual cortex, also known as visual area 1 (V1), Brodmann area 17, or the striate cortex. The extrastriate areas consist of visual areas 2, 3, 4, and 5.

Blindsight is the ability of people who are cortically blind to respond to visual stimuli that they do not consciously see due to lesions in the primary visual cortex, also known as the striate cortex or Brodmann Area 17. The term was coined by Lawrence Weiskrantz and his colleagues in a paper published in a 1974 issue of Brain. A previous paper studying the discriminatory capacity of a cortically blind patient was published in Nature in 1973. The assumed existence of blindsight is controversial, with some arguing that it is merely degraded conscious vision.

<span class="mw-page-title-main">Visual system</span> Body parts responsible for sight

The visual system comprises the sensory organ and parts of the central nervous system which gives organisms the sense of sight as well as enabling the formation of several non-image photo response functions. It detects and interprets information from the optical spectrum perceptible to that species to "build a representation" of the surrounding environment. The visual system carries out a number of complex tasks, including the reception of light and the formation of monocular neural representations, colour vision, the neural mechanisms underlying stereopsis and assessment of distances to and between objects, the identification of a particular object of interest, motion perception, the analysis and integration of visual information, pattern recognition, accurate motor coordination under visual guidance, and more. The neuropsychological side of visual information processing is known as visual perception, an abnormality of which is called visual impairment, and a complete absence of which is called blindness. Non-image forming visual functions, independent of visual perception, include the pupillary light reflex and circadian photoentrainment.

<span class="mw-page-title-main">Lateral geniculate nucleus</span> Component of the visual system in the brains thalamus

In neuroanatomy, the lateral geniculate nucleus 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. There are two LGNs, one on the left and another on the right side of the thalamus. In humans, both LGNs have six layers of neurons alternating with optic fibers.

<span class="mw-page-title-main">Retinal ganglion cell</span> Type of cell within the eye

A retinal ganglion cell (RGC) is a type of neuron located near the inner surface of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and retina amacrine cells. Retina amacrine cells, particularly narrow field cells, are important for creating functional subunits within the ganglion cell layer and making it so that ganglion cells can observe a small dot moving a small distance. Retinal ganglion cells collectively transmit image-forming and non-image forming visual information from the retina in the form of action potential to several regions in the thalamus, hypothalamus, and mesencephalon, or midbrain.

Parvocellular cells, also called P-cells, are neurons located within the parvocellular layers of the lateral geniculate nucleus (LGN) of the thalamus. "Parvus" is Latin for "small", and the name "parvocellular" refers to the small size of the cell compared to the larger magnocellular cells. Phylogenetically, parvocellular neurons are more modern than magnocellular ones.

<span class="mw-page-title-main">Superior colliculus</span> Structure in the midbrain

In neuroanatomy, the superior colliculus is a structure lying on the roof of the mammalian midbrain. In non-mammalian vertebrates, the homologous structure is known as the optic tectum, or optic lobe. The adjective form tectal is commonly used for both structures.

The opponent process is a color theory that states that the human visual system interprets information about color by processing signals from photoreceptor cells in an antagonistic manner. The opponent-process theory suggests that there are three opponent channels, each comprising an opposing color pair: red versus green, blue versus yellow, and black versus white (luminance). The theory was first proposed in 1892 by the German physiologist Ewald Hering.

<span class="mw-page-title-main">Koniocellular cell</span>

A koniocellular cell is a neuron with a small cell body that is located in the koniocellular layer of the lateral geniculate nucleus (LGN) in primates, including humans.

<span class="mw-page-title-main">Thalamocortical radiations</span> Neural pathways between the thalamus and cerebral cortex

In neuroanatomy, thalamocortical radiations also known as thalamocortical fibres, are the efferent fibres that project from the thalamus to distinct areas of the cerebral cortex. They form fibre bundles that emerge from the lateral surface of the thalamus.

Ocular dominance columns are stripes of neurons in the visual cortex of certain mammals that respond preferentially to input from one eye or the other. The columns span multiple cortical layers, and are laid out in a striped pattern across the surface of the striate cortex (V1). The stripes lie perpendicular to the orientation columns.

<span class="mw-page-title-main">Inferior temporal gyrus</span> One of three gyri of the temporal lobe of the brain

The inferior temporal gyrus is one of three gyri of the temporal lobe and is located below the middle temporal gyrus, connected behind with the inferior occipital gyrus; it also extends around the infero-lateral border on to the inferior surface of the temporal lobe, where it is limited by the inferior sulcus. This region is one of the higher levels of the ventral stream of visual processing, associated with the representation of objects, places, faces, and colors. It may also be involved in face perception, and in the recognition of numbers and words.

Blobs are sections of primary visual cortex above and below layer IV where groups of neurons sensitive to color assemble in cylindrical shapes. They were first identified in 1979 by Margaret Wong-Riley when she used a cytochrome oxidase stain, from which they get their name. These areas receive input from koniocellular cells in the dorsal lateral geniculate nucleus dLGN and output to the thin stripes of area V2. Interblobs are areas between blobs that receive the same input, but are sensitive to orientation instead of color. They output to the pale and thick stripes of area V2.

Visual perception is the ability to interpret the surrounding environment through photopic vision, color vision, scotopic vision, and mesopic vision, using light in the visible spectrum reflected by objects in the environment. This is different from visual acuity, which refers to how clearly a person sees. A person can have problems with visual perceptual processing even if they have 20/20 vision.

<span class="mw-page-title-main">Midget cell</span>

A midget cell is one type of retinal ganglion cell (RGC). Midget cells originate in the ganglion cell layer of the retina, and project to the parvocellular layers of the lateral geniculate nucleus (LGN). The axons of midget cells travel through the optic nerve and optic tract, ultimately synapsing with parvocellular cells in the LGN. These cells are known as midget retinal ganglion cells due to the small sizes of their dendritic trees and cell bodies. About 80% of RGCs are midget cells. They receive inputs from relatively few rods and cones. In many cases, they are connected to midget bipolar cells, which are linked to one cone each.

<span class="mw-page-title-main">Parasol cell</span>

A parasol cell, sometimes called an M cell or M ganglion cell, is one type of retinal ganglion cell (RGC) located in the ganglion cell layer of the retina. These cells project to magnocellular cells in the lateral geniculate nucleus (LGN) as part of the magnocellular pathway in the visual system. They have large cell bodies as well as extensive branching dendrite networks and as such have large receptive fields. Relative to other RGCs, they have fast conduction velocities. While they do show clear center-surround antagonism, they receive no information about color. Parasol ganglion cells contribute information about the motion and depth of objects to the visual system.

<span class="mw-page-title-main">Phantom contour</span>

A phantom contour is a type of illusory contour. Most illusory contours are seen in still images, such as the Kanizsa triangle and the Ehrenstein illusion. A phantom contour, however, is perceived in the presence of moving or flickering images with contrast reversal. The rapid, continuous alternation between opposing, but correlated, adjacent images creates the perception of a contour that is not physically present in the still images. Quaid et al. have also authored a PhD thesis on the phantom contour illusion and its spatiotemporal limits which maps out limits and proposes mechanisms for its perception centering around magnocellularly driven visual area MT.

<span class="mw-page-title-main">Visual processing abnormalities in schizophrenia</span>

Visual processing abnormalities in schizophrenia are commonly found, and contribute to poor social function.

<span class="mw-page-title-main">Visual masking</span>

Visual masking is a phenomenon of visual perception. It occurs when the visibility of one image, called a target, is reduced by the presence of another image, called a mask. The target might be invisible or appear to have reduced contrast or lightness. There are three different timing arrangements for masking: forward masking, backward masking, and simultaneous masking. In forward masking, the mask precedes the target. In backward masking the mask follows the target. In simultaneous masking, the mask and target are shown together. There are two different spatial arrangements for masking: pattern masking and metacontrast. Pattern masking occurs when the target and mask locations overlap. Metacontrast masking occurs when the mask does not overlap with the target location.

<span class="mw-page-title-main">Laura Busse</span> German neuroscientist

Laura Busse is a German neuroscientist and professor of Systemic Neuroscience within the Division of Neurobiology at the Ludwig Maximilian University of Munich. Busse's lab studies context-dependent visual processing in mouse models by performing large scale in vivo electrophysiological recordings in the thalamic and cortical circuits of awake and behaving mice.

References

  1. ↑ Freud, E; Plaut, DC; Behrmann, M (October 2016). "'What' Is Happening in the Dorsal Visual Pathway". Trends in Cognitive Sciences. 20 (10): 773–84. doi:10.1016/j.tics.2016.08.003. PMID   27615805. S2CID   3053257.
  2. 1 2 Wallace, DJ; Fitzpatrick, D; Kerr, JN (25 January 2016). "Primate Thalamus: More Than Meets an Eye". Current Biology. 26 (2): R60–1. doi: 10.1016/j.cub.2015.11.025 . PMID   26811887.
  3. 1 2 3 4 5 Brodal, Per (2010). The central nervous system : structure and function (4th ed.). New York: Oxford University Press. ISBN   978-0-19-538115-3.
  4. ↑ Carlson, Neil R. (2007). Physiology of behavior (9th ed.). Boston: Pearson/Allyn & Bacon. ISBN   978-0205467242.
  5. ↑ NB: "Parvus means "small" in Latin, per Latin Dictionary and "magnus" means large, per Latin Dictionary
  6. 1 2 Callaway EM (July 2005). "Structure and function of parallel pathways in the primate early visual system". The Journal of Physiology. 566 (Pt 1): 13–9. doi:10.1113/jphysiol.2005.088047. PMC   1464718 . PMID   15905213.
  7. 1 2 Nassi JJ, Callaway EM (May 2009). "Parallel processing strategies of the primate visual system". Nature Reviews. Neuroscience. 10 (5): 360–72. doi:10.1038/nrn2619. PMC   2771435 . PMID   19352403.
  8. 1 2 3 4 5 Stein J (2014-01-01). "Dyslexia: the Role of Vision and Visual Attention". Current Developmental Disorders Reports. 1 (4): 267–280. doi:10.1007/s40474-014-0030-6. PMC   4203994 . PMID   25346883.
  9. ↑ Jeffries, AM; Killian, NJ; Pezaris, JS (February 2014). "Mapping the primate lateral geniculate nucleus: a review of experiments and methods". Journal of Physiology, Paris. 108 (1): 3–10. doi:10.1016/j.jphysparis.2013.10.001. PMC   5446894 . PMID   24270042.
  10. 1 2 Pokorny J (July 2011). "Review: steady and pulsed pedestals, the how and why of post-receptoral pathway separation". Journal of Vision. 11 (5): 7. doi: 10.1167/11.5.7 . PMID   21737512.
  11. ↑ Cheng A, Eysel UT, Vidyasagar TR (October 2004). "The role of the magnocellular pathway in serial deployment of visual attention". The European Journal of Neuroscience. 20 (8): 2188–92. doi:10.1111/j.1460-9568.2004.03675.x. PMID   15450098. S2CID   31456201.
  12. ↑ Skottun BC, Skoyles JR (January 2011). "On identifying magnocellular and parvocellular responses on the basis of contrast-response functions". Schizophrenia Bulletin. 37 (1): 23–6. doi:10.1093/schbul/sbq114. PMC   3004196 . PMID   20929967.
  13. 1 2 Hebart MN, Hesselmann G (June 2012). "What visual information is processed in the human dorsal stream?". The Journal of Neuroscience. 32 (24): 8107–9. doi: 10.1523/JNEUROSCI.1462-12.2012 . PMC   6703654 . PMID   22699890.
  14. ↑ Poggio GF, Poggio T (1984). "The analysis of stereopsis". Annual Review of Neuroscience. 7: 379–412. doi:10.1146/annurev.ne.07.030184.002115. PMID   6370081. S2CID   18838554.
  15. 1 2 3 4 Vidyasagar TR (January 2004). "Neural underpinnings of dyslexia as a disorder of visuo-spatial attention". Clinical & Experimental Optometry. 87 (1): 4–10. doi:10.1111/j.1444-0938.2004.tb03138.x. PMID   14720113. S2CID   45931933.
  16. ↑ Jayakumar J, Dreher B, Vidyasagar TR (May 2013). "Tracking blue cone signals in the primate brain" (PDF). Clinical & Experimental Optometry. 96 (3): 259–66. doi:10.1111/j.1444-0938.2012.00819.x. hdl: 11343/39658 . PMID   23186138. S2CID   32259651.
  17. ↑ Burr DC, Morrone MC, Ross J (October 1994). "Selective suppression of the magnocellular visual pathway during saccadic eye movements". Nature. 371 (6497): 511–3. Bibcode:1994Natur.371..511B. doi:10.1038/371511a0. PMID   7935763. S2CID   4332938.
  18. ↑ Goodale MA, Westwood DA (2004). "An evolving view of duplex vision: separate but interacting cortical pathways for perception and action". Current Opinion in Neurobiology. 14 (2): 203–11. doi:10.1016/j.conb.2004.03.002. PMID   15082326. S2CID   15917985.
  19. 1 2 3 Bortolon C, Capdevielle D, Raffard S (June 2015). "Face recognition in schizophrenia disorder: A comprehensive review of behavioral, neuroimaging and neurophysiological studies". Neuroscience and Biobehavioral Reviews. 53: 79–107. doi:10.1016/j.neubiorev.2015.03.006. PMID   25800172. S2CID   20887067.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.