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→Primary visual cortex (V1): Reconnecting a sentence which was first added on 2005-11-16. A couple of paragraphs were erroneously inserted in the middle of this sentence on 2024-01-26.. |
→Primary visual cortex (V1): Added another reference for the assertion about parvo/magnocellular cells and V1 layers 4Cα/β. |
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Additionally, the functional significance of the striate cortex extends beyond its role as the primary visual cortex. It serves as a crucial hub for the initial processing of visual information, such as the analysis of basic features like orientation, spatial frequency, and color. The integration of these features in the striate cortex forms the foundation for more complex visual processing carried out in higher-order visual areas. Recent neuroimaging studies have contributed to a deeper understanding of the dynamic interactions within the striate cortex and its connections with other visual and non-visual brain regions, shedding light on the intricate neural circuits that underlie visual perception.<ref>{{cite journal |vauthors=Glickstein M, Rizzolatti G |title=Francesco Gennari and the structure of the cerebral cortex |journal=Trends in Neurosciences |volume=7 |issue=12 |pages=464–467 |date=1 December 1984|doi=10.1016/S0166-2236(84)80255-6 |s2cid=53168851 }}</ref>
The primary visual cortex is divided into six functionally distinct layers, labeled 1 to 6. Layer 4, which receives most visual input from the [[lateral geniculate nucleus]] (LGN), is further divided into 4 layers, labelled 4A, 4B, 4Cα, and 4Cβ. Sublamina 4Cα receives mostly [[Magnocellular cell|magnocellular]] input from the LGN, while layer 4Cβ receives input from [[Parvocellular cell|parvocellular]] pathways.<ref>{{cite journal | vauthors = Hubel DH, Wiesel TN | title = Laminar and columnar distribution of geniculo-cortical fibers in the macaque monkey | journal = The Journal of Comparative Neurology | volume = 146 | issue = 4 | pages = 421–450 | date = December 1972 | pmid = 4117368 | doi = 10.1002/cne.901460402 | s2cid = 6478458 }}</ref><ref>{{cite book |last1=Churchland |first1=Patricia Smith |last2=Sejnowski |first2=Terrence Joseph |author1-link=Patricia Churchland |author2-link=Terry Sejnowski |title=[[The Computational Brain]] |publisher=[[MIT Press]] |___location=Cambridge, Massachusetts |year=1992 |isbn=978-0-262-53120-7 |page=149}}</ref>
The average number of neurons in the adult human primary visual cortex in each hemisphere has been estimated at 140 million.<ref name="Leuba-Kraftsik-1994">{{cite journal | vauthors = Leuba G, Kraftsik R | title = Changes in volume, surface estimate, three-dimensional shape and total number of neurons of the human primary visual cortex from midgestation until old age | journal = Anatomy and Embryology | volume = 190 | issue = 4 | pages = 351–366 | date = October 1994 | pmid = 7840422 | doi = 10.1007/BF00187293 | s2cid = 28320951 }}</ref> The volume of each V1 area in an adult human is about 5400mm<math>{}^3</math> on average. A study of 25 hemispheres from 15 normal individuals with average age 59 years at autopsy found a very high variation, from 4272 to 7027mm<math>{}^3</math> for the right hemisphere (mean 5692mm<math>{}^3</math>), and from 3185 to 7568mm<math>{}^3</math> for the left hemisphere (mean 5119mm<math>{}^3</math>), with 0.81 correlation between left and right hemispheres.<ref>{{cite journal |last1=Andrews |first1=Timothy J. |last2=Halpern |first2=Scott D. |last3=Purves |first3=Dale |title=Correlated Size Variations in Human Visual Cortex, Lateral Geniculate Nucleus, and Optic Tract |journal=Journal of Neuroscience |date=1997 |volume=17 |issue=8 |pages=2859–2868 |doi=10.1523/JNEUROSCI.17-08-02859.1997 |doi-access=free}}</ref> The same study found average V1 area 2400mm<math>{}^2</math> per hemisphere, but with very high variability. (Right hemisphere mean 2477mm<math>{}^2</math>, range 1441–3221mm<math>{}^2</math>. Left hemisphere mean 2315mm<math>{}^2</math>, range 1438–3365mm<math>{}^2</math>.)
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