Angular gyrus

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Brain: Angular gyrus
Brain Surface Gyri.SVG
Gray1197.png
Drawing of a cast to illustrate the relations of the brain to the skull. (Angular gyrus labeled at upper left, in yellow section.)
Latin gyrus angularis
NeuroNames hier-91
NeuroLex ID birnlex_1376
TA A14.1.09.124
FMA FMA:61898
In this image, the angular gyrus is denoted by the double asterisk **

The angular gyrus is a region of the brain in the parietal lobe, that lies near the superior edge of the temporal lobe, and immediately posterior to the supramarginal gyrus; it is involved in a number of processes related to language, number processing and spatial cognition, memory retrieval, attention, and theory of mind. It is Brodmann area 39 of the human brain.

Anatomy[edit]

Left and right angular gyri are connected by the dorsal splenium and isthmus of the corpus collosum.[1] Both gyri lie between the four lobes.

Connections To the Angular gyrus
Connected To The Via the
ispilateral frontal and audallateral prefrontal and inferior frontal regions superior longitudinal fasciculus.[2]
caudate inferior occipitofrontal fasciculus[3]
parahippocampal gyrus[4] and hippocampus[3] inferior longitudinal fasciculus
precuneus and superior frontal gyrus occipitofrontal fasciculus,[5]
supramarginal gyrus local arcuate[6]

Function[edit]

The angular gyrus is the part of the brain associated with complex language functions (i.e. reading, writing and interpretation of what is written). Lesion to this part of the brain shows symptoms of the Gerstmann syndrome: effects include finger tap agnosia, alexia (inability to read), acalcula (inability to use arithmetic operations), agraphia (inability to copy), and left-right confusion.

Language[edit]

Geschwind proposed that written word is translated to internal monologue via the angular gyrus.[citation needed]

V. S. Ramachandran, and Edward Hubbard published a paper in 2003 in which they speculated that the angular gyrus is at least partially responsible for understanding metaphors. They stated:

There may be neurological disorders that disturb metaphor and synaesthesia.This has not been studied in detail but we have seen disturbances in the Bouba/Kiki effect (Ramachandran & Hubbard, 2001a) as well as with proverbs in patients with angular gyrus lesions. It would be interesting to see whether they have deficits in other types of synaesthetic metaphor, e.g. ‘sharp cheese’ or ‘loud shirt’. There are also hints that patients with right hemisphere lesions show problems with metaphor. It is possible that their deficits are mainly with spatial metaphors, such as ‘He stepped down as director’.[7]

The fact that the angular gyrus is proportionately much larger in hominids than other primates, and its strategic location at the crossroads of areas specialized for processing touch, hearing and vision, leads Ramachandran to believe that it is critical both to conceptual metaphors and to cross-modal abstractions more generally. However, recent research challenges this theory.

Research by Krish Sathian (Emory University) using functional magnetic resonance imaging (fMRI) suggests that the angular gyrus does not play a role in creating conceptual metaphors. Sathian theorizes that conceptual metaphors activate the texture-selective somatosensory cortex in the parietal operculum.[8]

Mathematics and Spatial Cognition[edit]

Since 1919, brain injuries to the angular gyrus have been known to often cause arithmetic deficits.[9][10] Functional imaging has shown that while other parts of the parietal lobe bilaterally are involved in approximate calculations due to its link with spatiovisual abilities, the left angular gyrus together with left Inferior frontal gyrus are involved in exact calculation due to verbal arithmetic fact retrieval.[11] When activation in the left angular gyrus is greater, a person's arithmetic skills are also more competent.[12]

The right angular gyrus has been associated with spatiovisual attention toward salient features.[13][14] It may allocate attention by employing a bottom-up strategy which draws on the area's ability to attend to retrieved memories.[13] For example, the angular gyrus plays a critical role in distinguishing left from right, by integrating conceptual understanding of the language term "left" or "right" with its location in space.[15] Furthermore, the angular gyrus has been associated with orienting in three dimensional space, not because it interprets space, but because it may control attention shifts in space.[16]

Other Functions[edit]

Default mode network[edit]

The angular gyrus is activated together with other brain regions when the mind is not engaged in an explicit task and does not have an obvious goal (referred to as the default mode network).[17]

Awareness[edit]

The angular gyrus reacts differently to intended and consequential movement.[18] This suggests that the angular gyrus monitors the self’s intended movements, and uses the added information to compute differently as it does for consequential movements. By recording the discrepancy, the angular gyrus maintains an awareness of the self.

Memory Retrieval[edit]

Activation of the angular gyrus shows that not only does it mediate memory retrieval, but notes contradictions between what is expected from the retrieval, and what is unusual.[1] The angular gyrus can access both content and episodic memories, and is useful in inferring from these the intentions of human characters.[13] Furthermore, the angular gyrus may use a feedback strategy to ascertain whether a retrieval is expected or unusual.

Out-of-body experiences[edit]

Recent experiments have demonstrated the possibility that stimulation of the angular gyrus is the cause of out-of-body experiences.[19] Stimulation of the angular gyrus in one experiment caused a woman to perceive a phantom existence behind her.[20] Another such experiment gave the test subject the sensation of being on the ceiling. This is attributed to a discrepancy in the actual position of the body, and the mind's perceived location of the body.

Clinical significance[edit]

Damage to the angular gyrus manifests as Gerstmann syndrome. Damage may impair one or more of the below functions.

  1. Dysgraphia/agraphia: deficiency in the ability to write[21][22]
  2. Dyscalculia/acalculia: difficulty in learning or comprehending mathematics[21][22]
  3. Finger agnosia: inability to distinguish the fingers on the hand[21][22]
  4. Left-right disorientation[21][22]

Additional images[edit]

References[edit]

  1. ^ a b Park HJ, Kim JJ, Lee SK, Seok JH, Chun J, Kim DI, and others. 2008. Corpus callosal connection mapping using cortical gray matter parcellation and DT-MRI. Human Brain Mapp 29(5):503–16. PMID 17133394
  2. ^ Nikos Makris, David N. Kennedy, Sean McInerney, A. Gregory Sorensen, Ruopeng Wang, Verne S. Caviness, Jr, and Deepak N. Pandya. Segmentation of Subcomponents within the Superior Longitudinal Fascicle in Humans: A Quantitative, In Vivo, DT-MRI Study. Cereb. Cortex (June 2005) 15(6): 854-869 first published online December 8, 2004 doi:10.1093/cercor/bhh186
  3. ^ a b Lucina Q. Uddin, Kaustubh Supekar, Hitha Amin, Elena Rykhlevskaia, Daniel A. Nguyen, Michael D. Greicius, and Vinod Menon. Dissociable Connectivity within Human Angular Gyrus and Intraparietal Sulcus: Evidence from Functional and Structural Connectivity. Cereb. Cortex (2010) 20(11): 2636-2646 first published online February 12, 2010 doi:10.1093/cercor/bhq011
  4. ^ Rushworth MF, Behrens TE, Johansen-Berg H (2006) Connection patterns distinguish 3 regions of human parietal cortex. Cereb Cortex 16:1418–1430.
  5. ^ Nikos Makris, George M. Papadimitriou, Scott Sorg, David N. Kennedy, Verne S. Caviness, Deepak N. Pandya, The occipitofrontal fascicle in humans: A quantitative, in vivo, DT-MRI study, NeuroImage, Volume 37, Issue 4, 1 October 2007, Pages 1100-1111, ISSN 1053-8119, 10.1016/j.neuroimage.2007.05.042. (http://www.sciencedirect.com/science/article/pii/S1053811907004405) Keywords: DT-MRI; Segmentation; Tractography; Occipitofrontal fascicle; Fronto-occipital fascicle
  6. ^ Lee H, Devlin JT, Shakeshaft C, Stewart LH, Brennan A, Glensman J, Pitcher K, Crinion J, Mechelli A, Frackowiak RS, Green DW, Price CJ (2007) Anatomical traces of vocabulary acquisition in the adolescent brain. J Neurosci 27:1184–1189.
  7. ^ Ramachandran, V.S., Hubbard, E.M, The Phenomenology of Synaesthesia, Journal of Consciousness Studies,10,No. 8,2003,pp. 49-57 [1]
  8. ^ Metaphorically feeling:Comprehending textual metaphros actives somatosensory cortex, Simon,K, Stilla,R, Sathian,K, Brain and Language, December 2011, ScienceDirect web site [2]
  9. ^ Henschen SL. (1919) On language, music and calculation mechanisms and their localisation in the cerebrum. Zeitschrift fur die gesamte Neurologie und Psychiatrie 52:273–298.
  10. ^ Gerstmann J. (1940). Syndrome of finger agnosia, disorientation for right and left, agraphia and acalculia—Local diagnostic value. Arch Neurol Psychiatry 44:398–408.
  11. ^ Dehaene S, Spelke E, Pinel P, Stanescu R, Tsivkin S. (1999). Sources of mathematical thinking: behavioral and brain-imaging evidence. Science. 284(5416):970-4. doi:10.1126/science.284.5416.970 PMID 10320379
  12. ^ Grabner RH, Ansari D, Reishofer G, Stern E, Ebner F, Neuper C. (2007).Individual differences in mathematical competence predict parietal brain activation during mental calculation. Neuroimage. 38(2):346-56. PMID 17851092
  13. ^ a b c Seghier M. L. (2012). The angular gyrus: multiple function ad multiple subdivisions. Neuroscientist (in press). PMID 22547530
  14. ^ Arsalidou M, Taylor MJ. 2011. Is 2+2=4? Meta-analyses of brain areas needed for numbers and calculations. Neuroimage 54(3):2382–93. PMID 20946958
  15. ^ Hirnstein M, Bayer U, Ellison A, Hausmann M. 2011. TMS over the left angular gyrus impairs the ability to discriminate left from right. Neuropsychologia 49(1):29–33. PMID 21035475
  16. ^ Chen Q, Weidner R, Vossel S, Weiss PH, Fink GR. Neural mechanisms of attentional reorienting in three-dimensional space. J Neurosci. 2012 Sep 26;32(39):13352-62.
  17. ^ Greicius MD, Krasnow B, Reiss AL, Menon V. 2003. Functional connectivity in the resting brain: a network analysis of the default mode hypothesis. Proc Natl Acad Sci U S A 100. PMID 12506194
  18. ^ Farrer C, Frey SH, Van Horn JD, Tunik E, Turk D, Inati S, Grafton ST. The angular gyrus computes action awareness representations. Centre de Neuroscience Cognitive.
  19. ^ Out-of-Body Experience? Your Brain Is to Blame - New York Times
  20. ^ Arzy, S., Seeck, M., Ortigue, S., Spinelli, L., Blanke, O., 2006. Induction of an illusory shadow person: Stimulation of a site on the brain's left hemisphere prompts the creepy feeling that somebody is close by. Nature, 443(21), pp.287.
  21. ^ a b c d Vallar G (July 2007). "Spatial neglect, Balint-Homes' and Gerstmann's syndrome, and other spatial disorders". CNS Spectr 12 (7): 527–36. PMID 17603404. 
  22. ^ a b c d Carota A, Di Pietro M, Ptak R, Poglia D, Schnider A (2004). "Defective spatial imagery with pure Gerstmann's syndrome". Eur. Neurol. 52 (1): 1–6. doi:10.1159/000079251. PMID 15218337. 

External links[edit]