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Posterior Parietal (posterior + parietal)
Terms modified by Posterior Parietal Selected AbstractsIndependent mechanisms for ventriloquism and multisensory integration as revealed by theta-burst stimulationEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2010Caterina Bertini Abstract The visual and auditory systems often concur to create a unified perceptual experience and to determine the localization of objects in the external world. Co-occurring auditory and visual stimuli in spatial coincidence are known to enhance performance of auditory localization due to the integration of stimuli from different sensory channels (i.e. multisensory integration). However, auditory localization of audiovisual stimuli presented at spatial disparity might also induce a mislocalization of the sound towards the visual stimulus (i.e. ventriloquism effect). Using repetitive transcranial magnetic stimulation we tested the role of right temporoparietal (rTPC), right occipital (rOC) and right posterior parietal (rPPC) cortex in an auditory localization task in which indices of ventriloquism and multisensory integration were computed. We found that suppression of rTPC excitability by means of continuous theta-burst stimulation (cTBS) reduced multisensory integration. No similar effect was found for cTBS over rOC. Moreover, inhibition of rOC, but not of rTPC, suppressed the visual bias in the contralateral hemifield. In contrast, cTBS over rPPC did not produce any modulation of ventriloquism or integrative effects. The double dissociation found in the present study suggests that ventriloquism and audiovisual multisensory integration are functionally independent phenomena and may be underpinned by partially different neural circuits. [source] Subjective mental time: the functional architecture of projecting the self to past and futureEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2009Shahar Arzy Abstract Human experience takes place in the line of mental time (MT) created through ,self-projection' of oneself to different time-points in the past or future. Here we manipulated self-projection in MT not only with respect to one's life events but also with respect to one's faces from different past and future time-points. Behavioural and event-related functional magnetic resonance imaging activity showed three independent effects characterized by (i) similarity between past recollection and future imagination, (ii) facilitation of judgements related to the future as compared with the past, and (iii) facilitation of judgements related to time-points distant from the present. These effects were found with respect to faces and events, and also suggest that brain mechanisms of MT are independent of whether actual life episodes have to be re-experienced or pre-experienced, recruiting a common cerebral network including the anteromedial temporal, posterior parietal, inferior frontal, temporo-parietal and insular cortices. These behavioural and neural data suggest that self-projection in time is a fundamental aspect of MT, relying on neural structures encoding memory, mental imagery and self. [source] Effector-independent representations of simple and complex imagined finger movements: a combined fMRI and TMS studyEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2003J. P. Kuhtz-Buschbeck Abstract Kinesthetic motor imagery and actual execution of movements share a common neural circuitry. Functional magnetic resonance imaging was used in 12 right-handed volunteers to study brain activity during motor imagery and execution of simple and complex unimanual finger movements of the dominant and the nondominant hand. In the simple task, a flexible object was rhythmically compressed between thumb, index and middle finger. The complex task was a sequential finger-to-thumb opposition movement. Premotor, posterior parietal and cerebellar regions were significantly more active during motor imagery of complex movements than during mental rehearsal of the simple task. In 10 of the subjects, we also used transcranial magnetic brain stimulation to examine corticospinal excitability during the same motor imagery tasks. Motor-evoked potentials increased significantly over values obtained in a reference condition (visual imagery) during imagery of the complex, but not of the simple movement. Imagery of finger movements of either hand activated left dorsal and ventral premotor areas and the supplementary motor cortex regardless of task complexity. The effector-independent activation of left premotor areas was particularly evident in the simple motor imagery task and suggests a left hemispherical dominance for kinesthetic movement representations in right-handed subjects. [source] Functional neuroanatomy of the parahippocampal region: The lateral and medial entorhinal areasHIPPOCAMPUS, Issue 9 2007Kristin M. Kerr Abstract The entorhinal cortex (EC) serves a pivotal role in corticohippocampal interactions, but a complete description of its extrinsic connections has not been presented. Here, we have summarized the cortical, subcortical, and hippocampal connections of the lateral entorhinal area (LEA) and the medial entorhinal area (MEA) in the rat. We found that the targets and relative strengths of the entorhinal connections are strikingly different for the LEA and MEA. For example, the LEA receives considerably heavier input from the piriform and insular cortices, whereas the MEA is more heavily targeted by the visual, posterior parietal, and retrosplenial cortices. Regarding subcortical connections, the LEA receives heavy input from the amygdala and olfactory structures, whereas the MEA is targeted by the dorsal thalamus, primarily the midline nuclei and also the dorsolateral and dorsoanterior thalamic nuclei. Differences in the LEA and MEA connections with hippocampal and parahippocampal structures are also described. In addition, because the EC is characterized by bands of intrinsic connectivity that span the LEA and MEA and project to different septotemporal levels of the dentate gyrus, special attention was paid to the efferents and afferents of those bands. Finally, we summarized the connections of the dorsocaudal MEA, the region in which the entorhinal "grid cells" were discovered. The subregional differences in entorhinal connectivity described here provide further evidence for functional diversity within the EC. It is hoped that these findings will inform future studies of the role of the EC in learning and memory. © 2007 Wiley-Liss, Inc. [source] Structural MRI biomarkers for preclinical and mild Alzheimer's disease,HUMAN BRAIN MAPPING, Issue 10 2009Christine Fennema-Notestine Abstract Noninvasive MRI biomarkers for Alzheimer's disease (AD) may enable earlier clinical diagnosis and the monitoring of therapeutic effectiveness. To assess potential neuroimaging biomarkers, the Alzheimer's Disease Neuroimaging Initiative is following normal controls (NC) and individuals with mild cognitive impairment (MCI) or AD. We applied high-throughput image analyses procedures to these data to demonstrate the feasibility of detecting subtle structural changes in prodromal AD. Raw DICOM scans (139 NC, 175 MCI, and 84 AD) were downloaded for analysis. Volumetric segmentation and cortical surface reconstruction produced continuous cortical surface maps and region-of-interest (ROI) measures. The MCI cohort was subdivided into single- (SMCI) and multiple-domain MCI (MMCI) based on neuropsychological performance. Repeated measures analyses of covariance were used to examine group and hemispheric effects while controlling for age, sex, and, for volumetric measures, intracranial vault. ROI analyses showed group differences for ventricular, temporal, posterior and rostral anterior cingulate, posterior parietal, and frontal regions. SMCI and NC differed within temporal, rostral posterior cingulate, inferior parietal, precuneus, and caudal midfrontal regions. With MMCI and AD, greater differences were evident in these regions and additional frontal and retrosplenial cortices; evidence for non-AD pathology in MMCI also was suggested. Mesial temporal right-dominant asymmetries were evident and did not interact with diagnosis. Our findings demonstrate that high-throughput methods provide numerous measures to detect subtle effects of prodromal AD, suggesting early and later stages of the preclinical state in this cross-sectional sample. These methods will enable a more complete longitudinal characterization and allow us to identify changes that are predictive of conversion to AD. Hum Brain Mapp 2009. © 2009 Wiley-Liss, Inc. [source] Amnestic mild cognitive impairment in Parkinson's disease: A brain perfusion SPECT study,,MOVEMENT DISORDERS, Issue 3 2009Flavio Nobili MD Abstract The purpose of this study was to investigate cortical dysfunction in Parkinson's disease (PD) patients with amnestic deficit (PD-MCI). Perfusion single photon emission computed tomography was performed in 15 PD-MCI patients and compared (statistical parametric mapping [SPM2]) with three groups, i.e., healthy subjects (CTR), cognitively intact PD patients (PD), and common amnestic MCI patients (aMCI). Age, depression, and UPDRS-III scores were considered as confounding variables. PD-MCI group (P < 0.05, false discovery rate,corrected for multiple comparisons) showed relative hypoperfusion in bilateral posterior parietal lobe and in right occipital lobe in comparison to CTR. As compared to aMCI, MCI-PD demonstrated hypoperfusion in bilateral posterior parietal and occipital areas, mainly right cuneus and angular gyrus, and left precuneus and middle occipital gyrus. With a less conservative threshold (uncorrected P < 0.01), MCI-PD showed hypoperfusion in a left parietal region, mainly including precuneus and inferior parietal lobule, and in a right temporal-parietal-occipital region, including middle occipital and superior temporal gyri, and cuneus-precuneus, as compared to PD. aMCI versus PD-MCI showed hypoperfusion in bilateral medial temporal lobe, anterior cingulate, and left orbitofrontal cortex. PD-MCI patients with amnestic deficit showed cortical dysfunction in bilateral posterior parietal and occipital lobes, a pattern that can be especially recognized versus both controls and common aMCI patients, and to a lesser extent versus cognitively intact PD. The relevance of this pattern in predicting dementia should be evaluated in longitudinal studies. © 2008 Movement Disorder Society [source] Functional changes of the cortical motor system in hereditary spastic paraparesisACTA NEUROLOGICA SCANDINAVICA, Issue 3 2009B. Koritnik Background,,, Hereditary spastic paraparesis (HSP) is a heterogeneous group of disorders characterized by progressive bilateral lower limb spasticity. Functional imaging studies in patients with corticospinal tract involvement have shown reorganization of motor circuitry. Our study investigates functional changes in sensorimotor brain areas in patients with HSP. Methods,,, Twelve subjects with HSP and 12 healthy subjects were studied. Functional magnetic resonance imaging (fMRI) was used to measure brain activation during right-hand finger tapping. Image analysis was performed using general linear model and regions of interest (ROI)-based approach. Weighted laterality indices (wLI) and anterior/posterior indicies (wAI and wPI) were calculated for predefined ROIs. Results and discussion,,, Comparing patients and controls at the same finger-tapping rate (1.8 Hz), there was increased fMRI activation in patients' bilateral posterior parietal cortex and left primary sensorimotor cortex. No differences were found when comparing patients and controls at 80% of their individual maximum tapping rates. wLI of the primary sensorimotor cortex was significantly lower in patients. Subjects with HSP also showed a relative increase in the activation of the posterior parietal and premotor areas compared with that of the primary sensorimotor cortex. Our findings demonstrate an altered pattern of cortical activation in subjects with HSP during motor task. The increased activation probably reflects reorganization of the cortical motor system. [source] Diploic venous anatomy studied in-vivo by MRICLINICAL ANATOMY, Issue 3 2009Khalil Jivraj Abstract Calvarial diploic venous anatomy has been studied post-mortem, but few studies have addressed these venous structures in-vivo. Previous work in our laboratory has shown that intraosseous infusion through the skull diploic space near the diploic veins in animals and humans does access the superior sagittal sinus and the systemic venous system. We developed a volumetric method of imaging the diploic veins in-vivo using MRI, intravenous gadolinium, and digital subtraction to provide for three-dimensional depiction and exact localization of these veins. We hypothesized that this technique would allow for an assessment of the probability of existence, distribution, and concentration of diploic veins in the skull. We scanned 31 neurosurgical patients, and were able to create 3D diploic venous maps in 74% of them. These maps were processed using Adobe Photoshop CS2. Mathworks MatLab 6.5, once customized, counted the number of pixels occupied by the diploic veins in the processed image. The probability of veins was highest in the occipital regions (100%). The inferior occipital (4.1%) and posterior parietal (4.1%) regions had the highest concentrations of diploic veins. Digital subtraction venography using a volumetric MRI sequence can demonstrate the diploic veins in-vivo. The inferior occipital region may be the best area for an intraosseous infusion device because it has the greatest likelihood of containing a vein and also has the highest concentration of veins. Clin. Anat. 22:296,301, 2009. © 2009 Wiley-Liss, Inc. 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