The lower temporal gyrus is a brain structure located in the lower part of the temporal lobe and an area we know to be responsible for visual perception and discrimination, as well as other functions that have been subsequently investigated, such as arithmetic and number processing.
In this article we explain what the lower temporal gyrus is, what its structure and location is, what functions it performs in the brain and what are the main disorders associated with damage to this brain structure.
Lower time rotation: definition, structure and location
The lower temporal gyrus is a convolution of the brain located, as its name suggests, at the bottom of the temporal lobe . This lobe consists of three convolutions on its lateral surface: the upper, the medial and the lower, which we will discuss throughout the article.
The convolutions or gyres are the folds that give the cerebral cortex its wrinkled appearance, the most developed area of the brain and the one in charge of higher cognitive functions such as thinking, language, planning or decision making.
The lower temporal gyrus is, as we mentioned, one of the three circumvolutions of the temporal lobe, one of the 6 main lobes of which each brain hemisphere consists and whose main functions involve the management of auditory language, participation in speech understanding systems, visual recognition of objects or identification of faces, among others.
The lower temporal gyrus is located at the lower lateral edge of each cerebral hemisphere, below the medial temporal gyrus and behind with the lower occipital gyrus . It extends around the inferolateral border to the inner surface of the temporal lobe, where it is bounded by the inferior sulcus.
It should also be noted that the main source of blood supply to this brain area comes from the four temporal branches of the middle cerebral artery that emerge from the lateral furrow or Silvio’s cleft, a groove that crosses the entire brain from its base and on both sides.
The lower temporal gyrus is a brain gyrus involved in visual object recognition and visual image processing , due to its connection with areas of the lower occipital gyrus that form the occipital lobe, the main brain structure related to visual perception and image interpretation and recognition, as well as spatial recognition or discrimination of movements and colours.
The lower time convolution also seems to specialize in the interpretation and processing of numbers . In a study in Palo Alto, USA, it was found that the lower temporal area was activated in a differentiated and significant way when participants were presented with different numbers and their digits (e.g., “45” or “9”), which was not the case if they were presented with letters (“forty-five” or “nine”) or homophonic words (e.g., “Hun” instead of “1”).
Although it was already known that this area of the brain was involved in the processing of visual information, with that and other research it was possible to conclude that this region was also involved in the arithmetic processing of numbers.
On the other hand, another study carried out in Japan using functional magnetic resonance showed that the lower left temporal gyrus played an important role in the writing of logograms (a system of characters or signs that represent a meaning on their own, used in languages such as Chinese) and, by extension, in other non-alphabetic languages.
Damage-related disorders in this structure
Injuries to a brain structure such as the lower temporal gyrus can lead to disorders such as visual agnosia , which involves an inability to identify, recognize and interpret visual stimuli. When a unilateral damage occurs, the functional specialisation of the cerebral hemispheres becomes evident: only the lesions on the right side affect the higher visual functions. And why does this happen?
In most people, the left hemisphere is the dominant one when it comes to language, as well as to the elaboration and interpretation of visual stimuli; while the right or non-dominant hemisphere would be specialized in non-verbal material and information, such as face recognition and emotional facial expressions. For this reason, the higher visual functions are only affected when there is damage to the right temporal area.
Another common disorder when a person suffers damage to the lower temporal gyrus and adjacent structures is prosopagnosia or face blindness , which causes an inability to recognize and discriminate faces, which can also lead to problems with objects or places.
Several studies have also concluded that damage to temporal lobe structures, specifically in the lower and medial temporal region, can lead to problems related to semantic memory, which is responsible for the recognition of the meaning of objects, vocabulary or general knowledge. This is what is observed in semantic dementia, a neurodegenerative disease characterized by the gradual loss of this type of memory, both at the verbal and non-verbal levels.
Finally, it should be noted that some research has concluded that lesions in the lower temporal gyrus would result in the agraphy of logographic writing systems , such as kanji (logograms used in the Japanese language) or Chinese characters. Agraphia affects a person’s ability to write correctly and usually occurs in conjunction with other language disorders such as aphasia and alexia.
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