angular gyrus

Brain: Angular gyrus
Figure one illustrates significant language areas of the brain. Brodmann area 39 is highlighted in red.
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

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, mathematics and cognition. It is Brodmann area 39 of the human brain.

Function

Language

Geschwind proposed that written word is translated to internal monologue via the angular gyrus.

V. S. Ramachandran, director of the Center for Brain and Cognition at the University of California, San Diego, directed a study that showed that the angular gyrus is at least partially responsible for understanding metaphors. Right-handed patients who had damage to their right angular gyrus and whose speaking and comprehending English was seemingly unaffected, could not grasp the dual nature of metaphor. Given a common metaphorical phrase, each patient could give only a literal meaning. If pressed, they could invent a wild interpretation but it was well off the mark^[1]

In another exercise, the patients did not describe a bulbous object as "booba" and a jagged object as "kiki," whereas more than 90% of unaffected subjects did so in the test. This showed an inability to connect visual stimuli to language.

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.

Out-of-body experiences

Recent experiments have demonstrated the possibility that stimulation of the angular gyrus is the cause of out-of-body experiences. ^[2] Stimulation of the angular gyrus in one experiment caused a woman to perceive a phantom existence behind her.^[3] 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.

Mathematics

Brain injuries to the angular gyrus since 1919 have been known to often cause arithmetic deficits.^[4][5] 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^[6] and this is greater the greater a person's mathematical abilities.^[7]

Additional images

Lateral surface of left cerebral hemisphere, viewed from above.

Lateral surface of left cerebral hemisphere, viewed from the side.

References

1. ^ V. S. Ramachandran, 2004. A Brief Tour of Human Consciousness. Pi Press, pp.60–82.
2. ^ Out-of-Body Experience? Your Brain Is to Blame - New York Times
3. ^ 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.
4. ^ 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.
5. ^ Gerstmann J. (1940). Syndrome of finger agnosia, disorientation for right and left, agraphia and acalculia—Local diagnostic value. Arch Neurol Psychiatry 44:398–408.
6. ^ 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. PMID 10320379
7. ^ 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

External links

• angular+gyrus at eMedicine Dictionary
• NIF Search - Angular Gyrus via the Neuroscience Information Framework