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Superior parietal lobule

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Last Updated: 02 July 2021

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Superior parietal lobule

Identifiers
Latinlobulus parietalis superior
NeuroNames106
TA98A14.1.09.130
TA25476
FMA61899

The Posterior parietal cortex comprises a region of the parietal cortex that is posterior to the primary somatosensory cortex and its adjacent sulcus, postcentral sulcus. The posterior parietal cortex itself is divided into upper and lower portion: superior parietal lobule and inferior parietal lobule, respectively. These two lobules are separate from one another by sulcus called intraparietal sulcus. The importance of the posterior parietal cortex to attention is perhaps best exemplified by a condition that can occur after damage to the posterior parietal cortex known as AS hemispatial or contralateral neglect. Hemispatial neglect is most frequently associated with damage to the posterior parietal cortex in the right cerebral hemisphere, after which patient ceases to devote attention to the left side of their body and visual field. These patients can act AS if they don't perceive anything in certain parts of their visual field; If asked to draw a picture, they will often not include a significant portion of the item draw, they may eat only about half of the food off of the plate, and shave or put makeup on only half of their face. Some patients may even deny that part of their body on neglected side is theirs in an attempt to reject the idea that they are suffering from a psychological condition. The posterior parietal cortex is also believed to be involved in some aspects of motor function, such AS planning movements and integrating visual information with movement to facilitate actions like reaching and grasping. Additionally, regions of the posterior parietal cortex are thought to contain neurons called mirror neurons, which are activated not only when particular action is performed but also when someone else is observed performing the same action. The true function of mirror neurons is yet to be determine. Some hypothesize that they are important for allowing us to learn by imitation, or even for understanding the actions of others; but there are also many who are critical of these hypotheses, arguing they are too speculative and lack evidential support. Additionally, posterior parietal cortex is thought to be involved in language AS well AS ability to understand numbers and arithmetic. Thus, its functions span a large spectrum, ranging from attention to movement to number processing. Research is still being done to better understand the role of the posterior parietal cortex in these actions and others. What is known about the posterior parietal cortex already, however, makes it one of the more intriguing areas in the brain.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Introduction

Cerebral asymmetry, which has been characterized by both its functions and its connections, is a fundamental property of the human brain and marker of successful development. The left hemisphere of the human brain preferentially mediates language ability, whereas the right hemisphere preferentially mediates visuospatial abilities. Many previous clinical, neuropsychological and transcranial magnetic stimulation studies have revealed that visuospatial attention was primarily controlled by right ventral posterior parietal cortex, whereas role of dorsal PPC subregions, especially superior parietal lobule in visuospatial attention, has not been well study. Mounting lesion - base studies have found that deficit in ventral inferior parietal lobule and temporo - parietal junction cause visuospatial neglect, and only a few studies observe lesion in dorsal PPC subregion, SPL, causing visuospatial neglect. However, evidence from functional neuroimaging studies has consistently revealed that SPL is involved in visuospatial attention. In addition, recent study using intraoperative electrical stimulation, which is considered to be the gold standard to determine brain function in awake patients during brain tumor surgery, shows that stimulation of right posterior SPL results in visuospatial neglect. Discrepancy between neuropsychological findings and findings obtained from brain damaged patients raises questions about the role of posterior SPL in visuospatial attention. To determine the relationship between the brain and behavior, TMS technique can be used to induce transient interruption of normal brain activity in relatively restricted area of the brain to directly and non - invasively assess whether brain area is involved in specific cognitive function. Thus, TMS provides a unique opportunity to study brain - behavior relations in healthy humans. In the current study, we use TMS to induce temporal virtual lesions in bilateral posterior SPL to determine the role of SPL in visuospatial attention. Visuospatial attention is considered to be primarily controlled by dorsal and ventral fronto - parietal attention network. Asymmetric dynamic balance between fronto - parietal networks in two hemispheres is considered to result in functional lateralization of visuospatial ability. In addition to fronto - parietal network, lesion - base studies in neglected patients have proposed unbalanced interhemispheric interactions between bilateral PPC to account for this hemispheric specialization of visuospatial function. Existing evidence indicates that functional asymmetry of visuospatial attention is substrated by brain networks. Therefore, we hypothesize that lateralization of visuospatial attention may be due to asymmetric anatomical connectivity between bilateral posterior SPLs with their involved fronto - parietal network and contralateral PPC. In our current study, we aim to directly test whether posterior SPL participates in visuospatial attention in healthy humans, and whether asymmetry of visuospatial attention exists in SPL using TMS technique. Furthermore, we use diffusion magnetic resonance imaging to further investigate the neuroanatomical basis of asymmetry of visuospatial attention. We firstly defined posterior SPL on the basis of SPL atlas construct with different anatomical connectivity patterns in our previous study. Secondly, repetitive TMS was applied separately to right and left posterior SPL to investigate the role of posterior SPL in visuospatial attention.


1.3.2 The Parietal Lobe

The parietal lobe is bound anteriorly by central sulcus, inferiorly by the posterior end of lateral sulcus, and posteriorly by imaginary borderline. The primary sensory, also know as somatosensory or somesthetic, cortex is found in the parietal lobe, major portion of which is postcentral gyrus. It is also known as sensory strip, but it is helpful to use the term somatosensory to help remember that bodily sensations, as opposed to visual and auditory sensations, are processed here. This gyrus lies directly posterior to the central sulcus, or rolandic fissure. This sensory cortex can map sensory control of various parts of the body. Somesthetic sensations are sent to the sensory cortex from opposite side of the body. This arrangement is a mirror image of a motor strip. Two gyri in parietal lobe are important to locating and becoming familiar with in regard to language. First is supramarginal gyrus, which curves around the posterior end of the lateral sylvian fissure. Second, angular gyrus, lies directly posterior to supramarginal gyrus. It curves around the end of prominent sulcus in the temporal lobe, superior temporal sulcus. Damage to area of angular gyrus in the dominant leave hemisphere may cause word - finding problems, reading and writing deficits, as well as leave - right disorientation, finger agnosia, and difficulty with arithmetic. Postcentral gyrus is the primary cortical area, whereas the majority of the remaining parietal lobe cortex is composed of the association cortex, mostly concerned with somatosensory and visual association function. The Parietal lobe has been characterized as an association area of association areas because of multimodal processing that takes place there. As a whole, parietal lobes may be most lateralize in function of all lobes in the cerebrum, although specialization is not complete. Language functions tend to be concentrated on the left parietal lobe around gyri just discuss. In the nondominant hemisphere, parietal lobe association cortex primarily processes spatial information and related selective attention. Damage here may result in difficulty attending to or complete neglect of the contralateral side of space. Visuospatial and constructional deficits may be found in testing patients with right - hemisphere parietal lobe damage.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Conclusions

Top: Dorsal Photograph of Einsteins brain with original labels. Bottom: Our identifications. 2 = angular; 3 = anterior occipital; c = central; e = processus acuminis; fm = midfrontal; fs = superior frontal; inp = intermediate posterior parietal; ip = intraparietal; m = marginal; mf = medial frontal; ocs = superior occipital; otr = transverse occipital; par = paroccipital; pci = precentral inferior; pcs = precentral superior; pma = marginal precentral; pme = medial precentral; po = parieto - occipital; prc = paracentral; ps = superior parietal; pst = transverse parietal; pti = postcentral inferior; pts = postcentral superior; rc = retrocalcarine; u = unnamed. K = presumed motor cortex for the right hand; K = knob representing motor cortex for the left hand. In both hemispheres, e limits anteriorly first annectant gyrus, pli de passage of Gratiolet that connects parietal and occipital lobes, indicated by red arrows. This figure is reproduced with permission from the National Museum of Health and Medicine. Top: Photographs of the left and right lateral surfaces of Einstein's brain take with the front of the brain rotating toward the viewer, with original labels. Bottom: Our identifications. Numbers 1 - 4 indicate four gyri in Einstein's right frontal lobe, rather than three. As is typical; K = knob representing motor cortex for the left hand. Submerge gyri are shade of red near diagonal sulcus on each side. It is clear from the left hemisphere that the posterior ascending limb of Sylvian fissure and postcentral inferior sulcus are not confluent, contrary to literature. Sulci: = additional inferior frontal; 1 = ascending branch of superior temporal sulcus; 2 = angular; aS = posterior ascending limb of Sylvian; c = central; d = diagonal; dt = descending terminal branch of Sylvian; fi = inferior frontal; fm = midfrontal; fs = superior frontal; ht = posterior terminal horizontal branch of Sylvian; ip = intraparietal; mf = medial frontal; pci = precentral inferior; pcs = precentral superior; pma = marginal precentral; pti = postcentral inferior; pts = postcentral superior; R = ascending ramus of anterior Sylvian fissure; R = horizontal ramus of anterior Sylvian fissure; S = Sylvian fissure; sa = sulcus acousticus; sca = subcentral anterior; scp = subcentral posterior; sip = intermedius primus of Jensen; ti = inferior temporal; tri = triangular; ts = superior temporal; tt = transverse temporal; u = unnamed; W = fronto - marginal of Wernicke. 1 = superior frontal gyrus; 2 = atypical superior middle frontal gyrus; 3 = atypical inferior middle frontal gyrus; 4 = inferior frontal gyrus. Figure reproduced with permission from the National Museum of Health and Medicine. Top: Photographs of the left and right lateral surfaces of Einstein's brain taken with the back of the brain rotating towards the viewer, with original labels.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Parietal lobe

The parietal lobe occupies about one quarter of each hemisphere and is involved in two primary functions: 1 sensation and perception and 2 integration and interpretation of sensory information, primarily with visual field. Thus, parietal lobe is responsible for integrating sensory input to form single perception cognition on one hand, while also forming a spatial coordinate system to represent our world, on the other hand. There is a range of clinical manifestations following injury to the parietal lobe, such as inability to understand spatial relations. In this article we will discuss the anatomy and function of parietal lobes, as well as its clinical relevance.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Anatomy

In TMS experiments, reaction times and accuracy for each subject were respectively record. We do not find significant differences between accuracy when TMS was separately applied in left or right posterior SPL. Anova identified significant differences in reaction times under conditions of sham stimulation, TMS on left SPL, and TMS on right SPL. Compared with sham stimulation, TMS applied on right posterior SPL induced an increment in reaction time. In addition, reaction times also differ when TMS is separately applied over left and right posterior SPLs. Reaction time was significantly longer when stimuli were applied in the right SPL than when they were applied in the left SPL. The Pair t - test also revealed that significantly longer reaction times were observed in spatial attention task test when stimuli were applied to the right SPL. In order to explore influences of different fronto - parietal pathways on asymmetry of visuospatial attention, we use different frontal subregions to reconstruct different fronto - parietal white matter pathways. Different white matter pathways between posterior SPL and frontal subregions were identify. The main fiber pathways that connect posterior SPL with SFG and posterior SPL with MFG are SLF I and SLF II, respectively, whereas the main fiber pathway that connects posterior SPL with IFG is EmC. Subsequently, pair t - tests and correlation analyses were respectively employed to investigate differences between hemispheres in anatomical connections of posterior SPL to each frontal subregion and to study whether asymmetric anatomical connections were related to asymmetry of visuospatial attention. Pair t - tests analysis revealed that significant differences between hemispheres in anatomical connections were found between posterior SPL and ipsilateral MFG. Correlation analysis unraveled that asymmetric connections of IFG and MFG with posterior SPL were significantly related to asymmetry of visuospatial attention.


Parietal lobe

Inferior and superior parietal lobules contain a constellation of visual subdivisions that can be distinguished on the basis of architectonic or connectional criteria, topographic organization, or other functional criteria. These subdivisions vary in their degree of sensory, motor, and multimodal function, with some areas appearing almost entirely visual sensory, others containing a high percentage of visuomotor neurons, and still others likely to be multimodal. Traditional views of visual functions of the parietal lobe have focused on its role in space perception, and lesions of this region produce visual neglect of associated visual field. However, recent anatomical and physiological studies suggest that this dorsal visual system consists of two separate streams that have different roles in visual spatial perception, eye movements, and arm and hand guidance. One stream, originating in the medial occipital cortex, provides visual information to areas V6A and MDP, which have complex sensory - motor functions related to arm movements to visual targets. In humans, lesions in presumed homologous regions of superior parietal lobule produce optic ataxia characterized by errors in reaching, particularly toward objects in visual periphery. The second dorsal stream reaches the parietal cortex through projections from areas MT and MST, which are direct primarily at subdivisions of inferior parietal lobule, areas VIP and LIPd. These cortical areas appear to utilize motion information to build representation of three - dimensional space. Unlike occipital areas, VIP appear to utilize vestibular and other sources of information to build a true head - center, rather than occulo - centric, representation of visual space. Area LIPd provides presaccadic activity that is used by frontal eye fields to guide eye movements to visually select targets. Cortical areas VIP and AIP of inferior parietal lobule are also involved in visual guidance of hand and arm movements, which is consistent with their connections with posterior visual areas and anterior somatosensory and motor cortex hand representations. In humans, lesions of presumed homologous areas of inferior parietal lobule produce a disorder know as apraxia, which involves inability to retrieve motor plans with respect to specific visual objects. This disorder exemplifies how IPL utilizes visual spatial information in conjunction with object shape information to guide specific hand movements. Thus, parietal cortex may best be viewed as a constellation of areas that provide spatial reference system to guide eye and arm - hand movements. However, visual areas of IPL also appear to utilize shape information to guide specific hand and arm movements necessary for appropriate manipulation of visually present objects. Finally, functional imaging studies have identified shape from motion - selective responses in parietal areas LIPd and LOP.


Superior Parietal Lobule

Large bundles of degenerated fibers leave superior parietal lobule and traverse centrum semiovale before entering the internal capsule. Some of these fibers leave superior lobule in nearly vertical direction to enter extreme and external capsules which they follow as routes to their distribution fields in claustrum and putamen. Additional degenerating fibers coursing through extreme capsule enter the dorsal portion of the insular cortex which contains numerous degenerating axon ramifications, especially abundant in infragranular layers. Field of very dense terminal degeneration occupies dorsal two - thirds, and tapers to a narrow lateral zone in the more ventral part of putamen. Terminal degeneration is also present in the body of caudate nucleus, but no degenerating fibers can be identified in the globus pallidus. Numerous degenerating axons descend from lesion in the superior parietal lobule through the internal capsule into the cerebral peduncle. At rostral levels of the subthalamic region, such fibers can be seen to terminate in moderate numbers in zona incerta and field H 2 of Forel, but no degenerated terminal fibers can be identified in the subthalamic nucleus. More massive termination of this brainstem projection is evident in pretectal area, superior colliculus, and pontine nuclei, but no degenerated terminal fibers can be identified in substantia nigra. Terminal degeneration is dense in pretectal region just medial or medioventral to nucleus limitans of Olszewski, 17 and also surrounds regio pretectalis anterior of Olszewski 17. Dense terminal degeneration occupies approximately vertical field at transition between superior colliculus and pretectal area. In the absence of adequate cytoarchitectonic study, it is not clear to what extent cellular organization of simian pretectal region corresponds to description of region in rat. In latter species, Bucher and Nauta 21 outline three major cell groups, viz., Nucleus pretectalis, nucleus pretectalis medialis and nucleus pretectalis profundus. In present cases of lesion of superior parietal lobule, very dense terminal degeneration appears in the ventrolateral part of pretectal area bound by nucleus limitans and nucleus suprageniculatus laterally, mesencaphalic reticular formation ventrally, and superior colliculus and nucleus of posterior commissure medially. It seems possible that this area corresponds to nucleus pretectalis profundus of rat. Corticocortical connections of superior lobule have not been fully map. It can nevertheless be demonstrated that lesions of superior parietal lobule elicit degeneration of fibers extending to contralateral superior and inferior parietal lobules, ipsilateral premotor cortex, precentrai and postcentral gyri, arcuate cortex, granular frontal cortex along dorsal and Ventral banks of principal sulcus, cingulate gyrus, inferior parietal lobule, insular cortex and superior temporal gyrus. Parieto - cingulate projection is substantial.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Clinical conditions

Optic ataxia is mostly observed after lesions of SPL and adjacent areas of IPS, including parieto - occipital junction. The hallmark of OA is misreaching, ie errors of hand movement end - point occurring mostly in peripheral visual field, but also in central vision when reaches are made in absence of visual feed - back. More recently, slowness of both arrest and directional corrections of hand movement, as well as inability to smoothly update hand movement trajectory have been reported in case of OA patient,s when sudden jump of target location in space occurs. Under these conditions, patients make two distinct movements, one to the first and the other to the second target's location, whereas normal subjects smoothly correct hand trajectory in - flight. In normal subjects, reversible inactivation of PPC through TMS affects accuracy of hand movement trajectory and prevents adaptation to new dynamics when movement is made in velocity - dependent force Field. In essence, main features of OA seem to be disorder composition and control of directional hand movements to visual targets, although impaired use of proprioceptive information has also been reported in these patients. Base on case report, it has been claimed that the essence of OA consists of problems in fast on - line control of reaching rather than in its early composition. However, more recent study performed on large number of OA patients with parietal lesions has found impaired reaching without impaired on - line control. Therefore, relative degree to which OA reflects deficit in motor planning or on - line motor control remains to be precisely determine. It has often been claimed that mild motor deficits observed in monkeys after parietal lesions do not provide a picture of involvement of the parietal cortex in visually - guide reaching that is comparable to that offered by OA in humans, and that conceptualization of the parieto - frontal system based on studies in monkeys over last 20 years would be of little help to understanding visual control of movement and its breakdown in parietal patients. We believe that this claim mostly reflects difficulty in interpreting behavioural consequences of parietal lobe lesion in monkeys. Most literature on this topic lacks consistency, since experiments could not be guided by detailed knowledge we now have of the architecture of the parieto - frontal system. From late fifties to about end of seventies, lesion studies report defects of visually - guide reaching after extensive PPC lesions encompassing SPL and IPL, but rather include both of them. This literature will not be discussed here. When neuropsychological studies on monkeys were guided by more advanced parcellation schemes of PPC, different pictures smoothly emerge. Misreaching in light was observed after bilateral removal of IPL areas 7A, 7ab and LIP, while reaching inaccuracy in dark was observed after bilateral lesions of SPL areas 5 and MIP, and of IPL area 7B.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Sources

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

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