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Angular gyrus
The angular gyrus is a region of the inferior parietal lobe, at the anterolateral region of the occipital lobe. As well as being a distinct region of the cortex, it functions to integrate and connect numerous surrounding regions.
Lesions of the angular gyrus can result in a range of symptoms, all evidenced by its various connections and interactions. In this article, the anatomy, integral function, and clinical relevance of the angular gyrus will be discussed.
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Anatomy and location
The angular gyrus is a horseshoe shaped region of the inferior parietal lobule. The region is located posterior to the supramarginal gyrus, the second region that forms the inferior parietal lobule. This region is known as the Brodmann area 39.
The two angular gyri are connected via the isthmus of the corpus callosum (a large white matter tract that connects the two cerebral hemispheres at the midline) and dorsal splenium (the most posterior region of the body of the corpus callosum). The location of the angular gyrus lies between the parietal, occipital, and temporal lobes. As such, it plays an essential role in the integration, processing, and connection of these different functional areas.
The blood supply to the angular gyrus arises from the middle cerebral artery; a primary branch of the internal carotid artery.
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Functions
The angular gyrus is involved in:
- spatial cognition
- language processes
- attention
- number processing
- memory retrieval
- social cognition
- conflict resolution
It is the region of the brain that is associated with complex language related functions (e.g. reading, writing) and being able to make sense of the meaning and content of written words.
Connections
The angular gyrus forms a range of connections with surrounding areas of the cortex. It has connections with the following regions of the cerebral cortex:
- ipsilateral prefrontal
- inferior and superior frontal
- opercular
These regions are involved in attention and calculation. The superior frontal gyrus is an essential region for simple things such as self-awareness and laughter. As it is not a distinct gyrus of the cerebral cortex (like the middle and inferior frontal gyri), it is more accurately described as a region. The angular gyrus also forms connections with the parahippocampal gyrus and hippocampus. These connections lead to the function of the angular gyrus in memory and spatial orientation.
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It also forms connections with the supramarginal gyrus, which lies just anterior to it. The supramarginal gyrus is involved in the processing of sensory modalities: proprioceptive, auditory, visual, and somatosensory. In addition, it forms connections with the caudate nucleus; one of the nuclei of the basal ganglia which is involved in the cognitive loop the brain.
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The superior longitudinal fasciculus forms a band of white matter tracts that connects the anterior and posterior areas of the cortex to each other. It is formed of three separate bundles, and a separate bundle called the arcuate fasciculus (which connects Wernicke’s area and Broca’s area). It connects the angular gyrus to the prefrontal and inferior frontal cortices.
Angular gyrus lesion
A lesion to the angular gyrus can result in problems with arithmetic, as well as writing, telling left from right, and the inability to tell one’s fingers apart. This syndrome is called Gerstmann syndrome, and may also manifest from damage to the fusiform gyrus.
Damage to the angular gyrus could also result in behavioural changes. Reduced activity in the angular gyrus is also seen in dyslexic patients, and makes logical sense, as dyslexia is a disease where the patient presents with difficulty in spelling, reading, and writing.
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