Parietal Lobe and Its Function顶叶及其功能
The parietal lobe is located between the central furrow and the occipital ridge. This part of the brain helps process the sense of touch and pain. Moreover, it participates in cognitive processes (1).
In this article, we will elaborate on the position, structure, and function of the parietal lobe. Importantly, we will mention some diseases and conditions that result from the parietal lobe damage.
Position and anatomy of the parietal lobe
The parietal lobe is the middle part of the brain. It is located behind the central furrow towards the back. It is separated by incision preoccipitalis from the occipital lobe, lying completely posteriorly (1).
The incisura preoccipitalis cuts into the upper convexity of the brain hemispheres. As a result, the gyrus postcentralis, in which there are sensory centers, belongs to the parietal lobe. There are two curves in the lower area of the parietal lobes. Those are the anterior, gyrus supramarginalis and posterior, gyrus angularis.
As already said, the parietal lobe occupies the upper side of the hemisphere. The parietal lobe limits from the anterior and lateral sides include the area from the front to the central sulcus, from the temporal floor to the lateral sulcus, from the occipital sulcus to the imaginary line that flows from the upper edge of the parietal occipital sulcus to the lower hemisphere edge.
The parietal lobe, like the frontal lobe, forms a significant part of the cerebral hemisphere. In the phylogenetic relationship, it distinguishes the old part - posterior central gyrus, the new part – the upper dark gyrus, and the newest - lower dark gyrus.
Functions of the parietal lobe
The parietal lobe is the center of the somatic senses. Most importantly, this part of the brain plays a significant role in identifying objects around us. Namely, it helps us understand spatial relationships, and correctly analyze and compare the position of one body concerning another or the observer himself. This lobe is also important for pain and touch interpretation.
Moreover, the parietal lobe is significant for interpreting words, as well as language understanding and processing (1). It helps interpret and realize temperature, vision, sensory, hearing, memory, and motor center signals, as well as visual perception.
Now, we will elaborate on anatomical parts of the parietal lobe about their specific functions. First of all, the postcentral gyrus of the parietal lobe (the primary somatosensory region) processes somatic sensory stimuli that serve to recognize the shape, composition, and weight of an object.
The spatial organization center also applies to the primary somatosensory cortex located in the anterior portions of the parietal lobe. The somatosensory functions of one side of the body are controlled by the contralateral hemisphere of the brain.
The posterolateral areas of the parietal lobe are responsible for creating visual and spatial information, that is, for trajectory information of moving objects. These areas are also responsible for proprioception (awareness of the position of body parts in space).
In the dominant hemisphere, the Gerstmann area located in the central part of the parietal lobe is responsible for the ability to compute, write, properly perceive space, especially the left-to-right orientation, and for finger recognition.
The nearby angular gyrus is responsible for naming things and other aspects of word recognition. The non-dominant parietal lobe participates in the integration of the contralateral side of the body into space and is responsible for navigating in the space.Finally, it plays an important role in different abilities such as drawing.
Furthermore, the posterior central gyrus houses the centers of sensitivity are projected with a projection of the body similar to that of the anterior central gyrus. A human face is projected in the lower third of the gyrus. The middle third segment projects a hand, while the foot is projected in the upper third part.
In the upper parietal gyrus, there are centers in charge of complex types of deep sensitivity: musculoskeletal, two-dimensional spatial sensation, sense of weight and volume of movement, sense of object recognition to the touch. The posterior to upper portions of the posterior central gyrus contain localized centers, providing the ability to identify one’s body, its parts, their proportions, and their relative position.
The most important sensory area is the parietal cortex segment of the postcentral gyrus. In addition, its corresponding part of the paracentral lobe plays a very important sensory role. These zones are called somatosensory region I.
There is a projection of skin sensitivity of the opposite side of the body from tactile, pain, temperature receptors, intereceptors of sensitivity, and systemic-skeletal sensitivity - from muscle receptors, joints, and tendons.
In addition to the somatosensory region I, there is a smaller size region called the somatosensory area II, located at the intersection of the central sulcus with the upper edge of the temporal lobe, at the depth of the lateral sulcus. The degree of localization of body parts is less pronounced.
Diseases and damage to the parietal brain lobe
Damage to the anterior portion of the parietal lobe may cause problems with the recognition of objects via the sense of touch. This condition is called asterognosis.
Lesions located laterally may cause interference with naming and other linguistic functions, as well as interference with writing, numeracy, left-to-right orientation, and finger naming. This condition is especially interesting from the medical point of view.
It is called the Gerstmann’s syndrome. It implies a disturbance or inability to distinguish the left and right sides of the body and space. Failure to recognize fingers, impaired computing, writing, and reading are also symptoms of this syndrome.
Causes of this syndrome in adults include impaired blood flow to this region. In other words, it results from the cerebrovascular disease. It can be a consequence of a stroke. Also, other types of brain damage can cause the Gerstmann’s syndrome. Moreover, a brain tumor in the parietal region can result in the occurrence of certain symptoms that are related to the Gerstmann syndrome.
成年人这种综合症的原因包括该区域的血液流动受损。换句话说，它是由脑血管疾病引起的，这可能是中风的后果。同样，其它类型的脑损伤也会导致格斯曼综合症。此外，顶叶区域的脑肿瘤可能导致与 Gerstmann 综合征相关的某些症状的发生。
When it comes to the occurrence of the Gerstmann syndrome in children, scientists do not have a certain conclusion. Possible causes include brain damage, even though there are patients who suffer from this syndrome and do not have brain damage.
Moreover, acute damage to the non-dominant parietal lobe can cause the contralateral side (usually left) to be neglected, leading to a diminished awareness of that part of the body, the environment around it, and injury to it.
For example, patients with severe damage to the right parietal lobe may negate left paresis and may be acutely disturbed. Patients with minor impairments may become impaired when performing motor tasks (eg, dressing or other daily activities) —a space-motor deficit called apraxia.
The Parietal Lobe Syndrome
Parietal lobe syndrome implies an outbreak of function of this lobe due to damage to its structures. This lobe is located between the frontal lobes in both cerebral hemispheres. The parietal lobe extends from the central sulcus to the parieto-occipital groove separating it from the occipital lobe. It contains the primary somatosensory cortex.
In the parietal lobe of the dominant hemisphere, the supramarginal and angular gyruses form part of the Wernike Speech Center. The fasciculus archuatus fibers connect the Broca’s and Wernike’s speech centers by passing through this lobe.
The parietal lobe of the dominant hemisphere is responsible for the ability to calculate (2), as well as the left-to-right orientation. In this lobe, body schemes are found.
In the depth of the parietal lobe of both hemispheres are found fibers of optical radiation. Disorders of the parietal lobe function can result from trauma, tumors, infection, vascular events, etc. Damage caused by trauma or by another etiological factor can impair the function of the frontal lobe as well as cause frontal lobe syndrome.
Parietal lobe syndrome primarily involves the appearance of contralateral hyposthesia. The sense of touch, pain, temperature, vibration, and proprioception are reduced even though the Edinger’s path and the system of medial leminiscus are usually preserved.
顶叶综合征主要表现为对侧感觉减退。触觉、疼痛、温度、振动和本体感觉减弱，尽管通常保留了 Edinger 的路径和内侧半月板系统。
Damage to the posterior parts of the parietal lobe causes a disruption of the perception of the position of the body parts in the joints (proprioception is impaired).
It also disrupts the ability to localize light or gentle touch accurately. The patient is unable to recognize objects by touch, which is called asterognosis. Such patients also have a disorder called agraphesthesia. Agraphesthesia is an inability to recognize the shapes or letters that are drawn on the patient’s skin (circle, triangle, square).
When it comes to parietal lobe syndrome, the phenomenon of sensory inattention is also present. When the patient is touching both hands at the same time, he is not aware of the touch on one of them because he does not feel it (3).
The parietal lobe occupies the upper side of the hemisphere. The function of the parietal lobe is related to the perception and analysis of sensitive stimuli, as well as spatial orientation. Several functional centers are concentrated in the parietal lobe convolutions.
Damage, tumor, or stroke that affects the parietal lobe can lead to significant impairments and dysfunctions. Those include the Parietal lobe syndrome and the Gerstmann syndrome.
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