Left Superior Parietal Gyrus Research Articles

Volumes of Lateral Temporal and Parietal Structures Distinguish Between Healthy Aging, Mild Cognitive Impairment, and Alzheimer's Disease

Distinguishing amnestic mild cognitive impairment (MCI) from Alzheimer's disease (AD) and healthy aging depends mainly on clinical evaluation, and, ultimately, on investigator's judgment. Clinical evaluation in vivo is based primarily on cognitive assessments. The present study explores the potential of volumetric magnetic resonance imaging of parietal and lateral temporal brain structures to support the diagnosis of AD and to distinguish AD patients from patients with MCI and healthy control subjects (HCS). 52 age-matched HCS, 18 patients with MCI, and 59 patients with probable late onset AD were investigated. Using computational, neuromorphometric procedures gray matter (GM) was automatically parcellated into 28 local regions of interest, the volumes of which were computed. The left hippocampus (sensitivity/specificity: 80.8-90.4%/55.6-86.4%) and the right hippocampus (73.1-90.4%/66.7-84.7%) provided highest diagnostic accuracy in separating all three diagnostic groups. Promising diagnostic values for distinguishing MCI from HCS were found for the left superior parietal gyrus (61.5%/55.6%) and left supramarginal gyrus (65.4%/66.7%), and for distinguishing subjects with MCI from AD patients for the right middle temporal gyrus (77.8%/79.7%), left inferior temporal gyrus (83.3%/72.9%), and right superior temporal gyrus (77.8%/71.2%). The left superior temporal pole (92.3%/84.7%), left parahippocampal gyrus (86.5%/81.4%), left Heschl's gyrus (86.5%/79.7%), and the right superior temporal pole (82.7%/78.0%) revealed most promising diagnostic values for distinguishing AD patients from HCS. Data revealed that lateral temporal and parietal GM volumes distinguish between HCS, MCI, and AD as accurate as hippocampal volumes do; hence, these volumes can be used in the diagnostic procedure. Results also suggest that cognitive functions associated with these brain regions, e.g., language and visuospatial abilities, may be tested more extensively to obtain additional information that might enhance the diagnostic accuracy further.

Neocortical thinning in “benign” mesial temporal lobe epilepsy

In refractory mesial temporal lobe epilepsy (MTLE) extrahippocampal and neocortical abnormalities have been described in patients with or without mesial temporal sclerosis (MTS). Recently we observed gray matter reductions in regions outside the hippocampus in benign MTLE with or without MTS. Cortical thickness has been proposed as a viable methodologic alternative for assessment of neuropathologic changes in extratemporal regions. Herein, we aimed to use this technique to describe cortical abnormalities in patients with benign TLE. Whole-brain cortical thickness analysis (FreeSurfer) was performed in 32 unrelated patients with benign TLE [16 patients with signs of MTS on magnetic resonance imaging (MRI), pMTLE; 16 without, nMTLE] and 44 healthy controls. In the pMTLE group, the most significant thinning was found in the sensorimotor cortex bilaterally but was more extensive in the left hemisphere (false discovery rate, p < 0.05). Other areas were localized in the occipital cortex, left supramarginal gyrus, left superior parietal gyrus, left paracentral sulcus, left inferior/middle/superior frontal gyrus, left inferior frontal sulcus, right cingulate cortex, right superior frontal gyrus, right inferior parietal gyrus, right fusiform gyrus, and cuneus/precuneus. In the nMTLE, a similar neurodegenerative pattern was detected, although not surviving correction for multiple comparisons. Direct comparison between pMTLE and nMTLE did not reveal significant changes. Patients with either benign pMTLE or nMTLE showed comparable cortical thinning, mainly confined to the sensorimotor cortex. This finding that is not appreciated on routine MRI supports the hypothesis that similar to refractory MTLE, even in benign MTLE, pathology in neocortical regions maybe implicated in the pathophysiology of this syndrome.

Fronto-limbic dysfunction in borderline personality disorder: A 18F-FDG positron emission tomography study

IntroductionSeveral functional neuroimaging studies have demonstrated abnormalities in fronto-limbic pathways when comparing borderline personality disorder (BPD) patients with controls. The present study aimed to evaluate regional cerebral metabolism in euthymic BPD patients with similar measured impulsivity levels by means of 18F-FDG PET during resting state and to compare them against a control group. MethodsThe present study evaluates regional cerebral metabolism in 8 euthymic BPD patients with 18F-FDG PET during resting state as compared to 8 controls with similar socio-geographic characteristics. ResultsBPD patients presented a marked hypo-metabolism in frontal lobe and showed hyper-metabolism in motor cortex (paracentral lobules and post-central cortex), medial and anterior cingulus, occipital lobe, temporal pole, left superior parietal gyrus and right superior frontal gyrus. No significant differences appeared in basal ganglia or thalamus. ConclusionsResults reveal a dysfunction in patients' frontolimbic network during rest and provide further evidence for the importance of these regions in relation to BPD symptomatology.

Neurocognitive effects of HF-rTMS over the dorsolateral prefrontal cortex on the attentional processing of emotional information in healthy women: An event-related fMRI study

Current evidence concerning the neurocircuitry underlying the interplay between attention and emotion is mainly correlational. We used high-frequency repetitive Transcranial Magnetic Stimulation (HF-rTMS) to experimentally manipulate activity within the right or left dorsolateral prefrontal cortex (DLPFC) of healthy women and examined changes in attentional processing of emotional information using an emotional modification of the exogenous cueing task during event-related fMRI. Right prefrontal HF-rTMS resulted in impaired disengagement from angry faces, associated with decreased activation within the right DLPFC, dorsal anterior cingulate cortex (dACC) and left superior parietal gyrus, combined with increased activity within the right amygdala. Left prefrontal HF-rTMS resulted in diminished attentional engagement by angry faces and was associated with increased activity within the right DLPFC, dACC, right superior parietal gyrus and left orbitofrontal cortex. The present observations are in line with reports of a functionally interactive network of cortical-limbic pathways that play a central role in emotion regulation.

The neural network sustaining the crossmodal processing of human gender from faces and voices: An fMRI study

The aim of this fMRI study was to investigate the cerebral crossmodal interactions between human faces and voices during a gender categorization task.Twelve healthy male participants took part to the study. They were scanned in 4 runs that contained 3 conditions consisting in the presentation of faces, voices or congruent face–voice pairs. The task consisted in categorizing each trial (visual, auditory or associations) according to its gender (male or female).The subtraction between the bimodal condition and the sum of the unimodal ones showed that categorizing face/voice associations according to their gender produced unimodal activations of the visual (right calcarine sulcus) and auditory regions (bilateral superior temporal gyri), and specific supramodal activations of the left superior parietal gyrus and the right inferior frontal gyrus. Moreover, psychophysiological interaction analyses (PPI) revealed that both unimodal regions were inter-connected and connected to the prefrontal gyrus and the putamen, and that the left parietal gyrus had an enhanced connectivity with a parieto-premotor circuit involved in the crossmodal control of attention.This fMRI study showed that the crossmodal auditory–visual categorization of human gender is sustained by a network of cerebral regions highly similar to those observed in our previous studies examining the crossmodal interactions involved in face/voice recognition (Joassin et al., 2010). This suggests that the crossmodal processing of human stimuli requires the activation of a network of cortical regions, including both unimodal visual and auditory regions and supramodal parietal and frontal regions involved in the integration of both faces and voices and in the crossmodal attentional processes, and activated independently from the task to perform or the cognitive level of processing.

Central and peripheral components of writing critically depend on a defined area of the dominant superior parietal gyrus

Classical neuropsychological models of writing separate central (linguistic) processes common to oral spelling, writing and typing from peripheral (motor) processes that are modality specific. Damage to the left superior parietal gyrus, an area of the cortex involved in peripheral processes specific to handwriting, should generate distorted graphemes but not misspelled words, while damage to other areas of the cortex like the frontal lobe should produce alterations in written and oral spelling without distorted graphemes. We describe the clinical and neuropsychological features of a patient with combined agraphia for handwriting and typewriting bearing a small glioblastoma in the left parietal lobe. His agraphia resolved after antiedema therapy and we tested by bipolar cortical stimulation his handwriting abilities during an awake neurosurgical procedure. We found that we could reversibly re-induce the same defects of writing by stimulating during surgery a limited area of the superior parietal gyrus in the same patient and in an independent patient that was never agraphic before the operation. In those patients stimulation caused spelling errors, poorly formed letters and in some cases a complete cessation of writing with minimal or no effects on oral spelling. Our results suggest that stimulating a specific area in the superior parietal gyrus we can generate different patterns of agraphia. Moreover, our findings also suggest that some of the central processes specific for typing and handwriting converge with motor processes at least in the limited portion of the superior parietal gyrus we mapped in our patients.

Long-range EEG phase synchronization during an arithmetic task indexes a coherent cortical network simultaneously measured by fMRI

An open question lies in whether or not distributed activities in the distant brain regions are integrated into a coherent ensemble for cognitive information processing. Long-range phase synchronization is often observed by scalp EEG measurements during cognitive tasks and is considered to provide a possible neural principle for the functional integration of distributed neural activities. Synchronization could be reflected at the neuron firing level or at the local field potential and could appear in the scalp EEG under certain conditions on neural spatial and temporal coherence. To examine if phase synchronization is concerned with the integration of distant regions, we proposed a method to extract brain activities associated with task-dependent phase synchronization by combining simultaneous fMRI and EEG. By applying this method in a mental arithmetic task, we found a dominant task-dependent increase of phase synchronization around 14 Hz (in beta frequency) across bilateral parietal sites that were associated with both negative and positive BOLD responses. Functional connectivity analyses of these regions demonstrated that an increase in hemispheric beta synchronization was associated with a linking between the cross-hemispheric regions (left angular gyrus and right superior parietal gyrus) and also among the anterior–posterior regions (right dorsolateral prefrontal cortex, putamen, and right superior temporal gyrus). These findings indicate that the positive BOLD regions (dorsolateral prefrontal cortex and superior parietal lobule) are linked with other negative BOLD regions. We also discussed the possible importance of beta synchronization in the formation of a working memory network.

Exploring the unity and diversity of the neural substrates of executive functioning.

Previous studies exploring the neural substrates of executive functioning used task-specific analyses, which might not be the most appropriate approach due to the difficulty of precisely isolating executive functions. Consequently, the aim of this study was to use positron emission tomography (PET) to reexamine by conjunction and interaction paradigms the cerebral areas associated with three executive processes (updating, shifting, and inhibition). Three conjunction analyses allowed us to isolate the cerebral areas common to tasks selected to tap into the same executive process. A global conjunction analysis demonstrated that foci of activation common to all tasks were observed in the right intraparietal sulcus, the left superior parietal gyrus, and at a lower statistical threshold, the left lateral prefrontal cortex. These regions thus seem to play a general role in executive functioning. The right intraparietal sulcus seems to play a role in selective attention to relevant stimuli and in suppression of irrelevant information. The left superior parietal region is involved in amodal switching/integration processes. One hypothesis regarding the functional role of the lateral prefrontal cortex is that monitoring and temporal organization of cognitive processes are necessary to carry out ongoing tasks. Finally, interaction analyses showed that specific prefrontal cerebral areas were associated with each executive process. The results of this neuroimaging study are in agreement with cognitive studies demonstrating that executive functioning is characterized by both unity and diversity of processes.

The neural substrate of arithmetic operations and procedure complexity

Recent functional neuroimaging studies have begun to clarify how the human brain performs the everyday activities that require mental calculation. We used fMRI to test the hypotheses that there are specific neural networks dedicated to performing an arithmetic operation (e.g. + or −) and to performing processes that support more complex calculations. We found that the right inferior parietal lobule, left precuneus and left superior parietal gyrus are relatively specific for performing subtraction; and bilateral medial frontal/cingulate cortex are relatively specific for supporting arithmetic procedure complexity. We also found that greater difficulty level was associated with activation in a brain network including left inferior intraparietal sulcus, left inferior frontal gyrus and bilateral cingulate. Our results suggest that the network activated by the simplest calculation serves as a common basis, to which more regions are recruited for more difficult problems or different arithmetic operations.

Learning about pain: the neural substrate of the prediction error for aversive events.

Associative learning is thought to depend on detecting mismatches between actual and expected experiences. With functional magnetic resonance imaging (FMRI), we studied brain activity during different types of mismatch in a paradigm where contrasting-colored lights signaled the delivery of painful heat, nonpainful warmth, or no stimulation. When painful heat stimulation was unexpected, there was increased FMRI signal intensity in areas of the hippocampus, superior frontal gyrus, cerebellum, and superior parietal gyrus that was not found with mismatch between expectation and delivery of nonpainful warmth stimulation. When painful heat stimulation was unexpectedly omitted, the FMRI signal intensity decreased in the left superior parietal gyrus and increased in the other regions. These contrasting activation patterns correspond to two different mismatch concepts in theories of associative learning (Rescorla-Wagner, temporal difference vs. Pearce-Hall, Mackintosh). Searching for interventions to specifically modulate activation of these brain regions therefore offers an approach to identifying new treatments for chronic pain, which often has a substantial associative learning component.

Cortical fields participating in form and colour discrimination in the human brain

In order to map the anatomical structures participating in the analysis and processing of visual information related to discrimination of form and colour, we measured with positron emission tomography (PET) regional cerebral blood flow (rCBF) as an indicator of metabolic activity in ten right-handed volunteers during visual discrimination tasks, namely reference, form and colour tasks. Form discrimination specifically increased rCBF bilaterally in the inferior temporal and cingulate gyri, and in the left superior temporal, left occipital lateral, and left angular gyri, whereas colour discrimination did so in the left occipital superior and lateral, left parahippocampal, left occipito-temporal medial (lingual), and left superior parietal gyri, and the right precuneus.