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=                           Angular_gyrus                            =
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                            Introduction
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The angular gyrus is a region of the brain lying mainly in the
posteroinferior region of the parietal lobe, occupying the posterior
part of the inferior parietal lobule. It represents the Brodmann area
39.

Its significance is in transferring visual information to Wernicke's
area, in order to make meaning out of visually perceived words. It is
also involved in a number of processes related to language, number
processing and spatial cognition, memory retrieval, attention, and
theory of mind.


Connections
=============
Left and right angular gyri are connected by the dorsal splenium and
isthmus of the corpus callosum.

Connections To the Angular gyrus
Connected To The         Via the
|ipsilateral frontal and caudallateral prefrontal and inferior
frontal regions |superior longitudinal fasciculus.
|caudate        |inferior occipitofrontal fasciculus
|parahippocampal gyrus and hippocampus  |inferior longitudinal
fasciculus
|precuneus and superior frontal gyrus   |occipitofrontal fasciculus,
|supramarginal gyrus    |local arcuate


Boundaries
============
* Anteriorly by the supramarginal gyrus.
* Superiorly by the intraparietal sulcus.
* Posteriorly by the parieto-occipital sulcus.
* Inferiorly the angular gyrus of the parietal lobe is continuous as
the superior and middle temporal gyri. Also, the angular sulcus, which
is capped by the angular gyrus, is continuous as the superior temporal
sulcus inferiorly.


                              Function
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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 agnosia, alexia (inability
to read), acalculia (inability to use arithmetic operations), agraphia
(inability to copy), and left-right confusion.


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

V. S. Ramachandran, and Edward Hubbard published a paper in 2003 in
which they hypothesized the angular gyrus to play a role in
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'.

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.

Brownsett and Wise highlight the role of the left angular gyrus in
both speaking and writing.


Arithmetic and spatial cognition
==================================
Since 1919, brain injuries to the angular gyrus have been known to
often cause arithmetic deficits. 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.
When activation in the left angular gyrus is greater, a person's
arithmetic skills are also more competent.


Attention
===========
The right angular gyrus has been associated with spatiovisual
attention toward salient features. It may allocate attention by
employing a bottom-up strategy which draws on the area's ability to
attend to retrieved memories. For example, the angular gyrus plays a
critical role in distinguishing left from right by integrating the
conceptual understanding of the language term "left" or "right" with
its location in space. 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.


Default mode network
======================
The angular gyrus is part of the default mode network, a network of
brain regions activated during multi-modal activities that are
independent of external stimuli.


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


Out-of-body experiences
=========================
Experiments have demonstrated the ability of stimulation of the right
angular gyrus to induce out-of-body experiences. Stimulation of the
left angular gyrus in one experiment caused a woman to perceive a
shadowy person lurking behind her. The shadowy figure is actually a
perceived double of the self. 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
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Damage to the angular gyrus manifests as Gerstmann syndrome. Damage
may impair one or more of the below functions.
# Dysgraphia/agraphia: deficiency in the ability to write
# Dyscalculia/acalculia: difficulty in learning or comprehending
mathematics
# Finger agnosia: inability to distinguish the fingers on the hand
# Left-right disorientation


                         Additional images
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File:Angular gyrus animation small.gif|Position of angular gyrus
(shown in red).
File:Gray725 angular gyrus.png|Lateral surface of left cerebral
hemisphere, viewed from above. Angular gyrus is shown in orange.
File:Gray726 angular gyrus.png|Lateral surface of left cerebral
hemisphere, viewed from the side. Angular gyrus is shown in orange.
Image:Gehirn, lateral - Hauptgyri beschriftet.svg|Lateral view of a
human brain, main gyri labeled.

File:Slide3HAN.JPG|Cerebrum. Lateral view.Deep dissection.
File:Slide4HAN.JPG|Cerebrum. Lateral view.Deep dissection.
File:Angular gyrus coronal sections.gif|Angular gyrus highlighted in
green on coronal T1 MRI image
File:Angular gyrus sagittal sections.gif|Angular gyrus highlighted in
green on sagittal T1 MRI image
File:Angular gyrus transversal sections.gif|Angular gyrus highlighted
in green on transversal T1 MRI image


                              See also
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* Temporoparietal junction


                           External links
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*
[https://www.neuinfo.org/mynif/search.php?q=Angular%20Gyrus&t=data&s=cover&b=0&r=20
NIF Search - Angular Gyrus] via the Neuroscience Information Framework


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