The role of right and left parietal lobes in the conceptual processing of numbers

Neuropsychological and functional imaging studies have associated the conceptual processing of numbers with bilateral parietal regions (including intraparietal sulcus). However, the processes driving these effects remain unclear because both left and right posterior parietal regions are activated by many other conceptual, perceptual, attention, and response-selection processes. To dissociate parietal activation that is number-selective from parietal activation related to other stimulus or response-selection processes, we used fMRI to compare numbers and object names during exactly the same conceptual and perceptual tasks while factoring out activations correlating with response times. We found that right parietal activation was higher for conceptual decisions on numbers relative to the same tasks on object names, even when response time effects were fully factored out. In contrast, left parietal activation for numbers was equally involved in conceptual processing of object names. We suggest that left parietal activation for numbers reflects a range of processes, including the retrieval of learnt facts that are also involved in conceptual decisions on object names. In contrast, number selectivity in right parietal cortex reflects processes that are more involved in conceptual decisions on numbers than object names. Our results generate a new set of hypotheses that have implications for the design of future behavioral and functional imaging studies of patients with left and right parietal damage

Association between cognitive performance and cortical glucose metabolism in patients with mild Alzheimer's disease

Background: Neuronal and synaptic function in Alzheimer's disease (AD) is measured in vivo by glucose metabolism using positron emission tomography (PET). Objective: We hypothesized that neuronal activation as measured by PET is a more sensitive index of neuronal dysfunction than activity during rest. We investigated if the correlations between dementia severity as measured with the Mini Mental State Examination (MMSE) and glucose metabolism are an artifact of brain atrophy. Method: Glucose metabolism was measured using {[}F-18]fluorodeoxyglucose PET during rest and activation due to audiovisual stimulation in 13 mild to moderate AD patients (MMSE score >= 17). PET data were corrected for brain atrophy. Results: In the rest condition, glucose metabolism was correlated with the MMSE score primarily within the posterior cingulate and parietal lobes. For the activation condition, additional correlations were within the primary and association audiovisual areas. Most local maxima remained significant after correcting for brain atrophy. Conclusion: PET activity measured during audiovisual stimulation was more sensitive to functional alterations in glucose metabolism in AD patients compared to the resting PET. The association between glucose metabolism and MMSE score was not dependent on brain atrophy. Copyright (C) 2005 S. Karger AG, Basel

Brain injury due to persistent hyperinsulinemic hypoglycemia of infancy

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Imaging Studies of Aging, Neurodegenerative Disease, and Alcoholism.

Neurodegenerative diseases such as Alzheimers disease, disorders such as alcoholism, and the aging process can lead to impaired cognitive function and dementia. Researchers and clinicians have used noninvasive imaging techniques to determine the structural and physiological alterations in the brain that are associated with these conditions. Analyses of the brains structure have found that shrinkage (atrophy) of the brain tissue is characteristic for all conditions associated with dementia, but that the specific locations of atrophied brain structures vary among different neurodegenerative diseases and alcohol-induced disorders. Similarly, studies analyzing the metabolism in various brain structures have found that, depending on whether dementia was induced by neurodegenerative diseases, alcoholism, or aging, the affected brain structures vary slightly. Based on such studies, researchers and clinicians now can more accurately define different types of dementia and predict their clinical course

Rates of lobar atrophy in asymptomatic MAPT mutation carriers.

IntroductionThe aim of this study was to investigate the rates of lobar atrophy in the asymptomatic microtubule-associated protein tau (MAPT) mutation carriers.MethodsMAPT mutation carriers (n = 14; 10 asymptomatic, 4 converters from asymptomatic to symptomatic) and noncarriers (n = 13) underwent structural magnetic resonance imaging and were followed annually with a median of 9.2 years. Longitudinal changes in lobar atrophy were analyzed using the tensor-based morphometry with symmetric normalization algorithm.ResultsThe rate of temporal lobe atrophy in asymptomatic MAPT mutation carriers was faster than that in noncarriers. Although the greatest rate of atrophy was observed in the temporal lobe in converters, they also had increased atrophy rates in the frontal and parietal lobes compared to noncarriers.DiscussionAccelerated decline in temporal lobe volume occurs in asymptomatic MAPT mutation carriers followed by the frontal and parietal lobe in those who have become symptomatic. The findings have implications for monitoring the progression of neurodegeneration during clinical trials in asymptomatic MAPT mutation carriers

Brain Localisation of Memory Chunks in Chessplayers

Chess experts store domain-specific representations in their long-term memory; due to the activation of such representations, they perform with high accuracy in tasks that require the maintenance of previously seen information. Chunk-based theories of expertise (chunking theory: Chase & Simon, 1973; template theory: Gobet & Simon, 1996) state that expertise is acquired mainly by the acquisition and storage in long-term memory of familiar chunks that allow quick recognition. We tested some predictions of these theories by using fMRI while chessplayers performed a recognition memory task. These theories predict that chessplayers access long-term memory chunks of domain-specific information, which are presumably stored in the temporal lobes. We also predicted that the recognition memory tasks would activate working memory areas in the frontal and parietal lobes. These predictions were supported by the data

Characterization of the Community Structure of Large Scale Functional Brain Networks During Ketamine-Medetomidine Anesthetic Induction

One of the central questions in neuroscience is to understand the way communication is organized in the brain, trying to comprehend how cognitive capacities or physiological states of the organism are potentially related to brain activities involving interactions of several brain areas. One important characteristic of the functional brain networks is that they are modularly structured, being this modular architecture regarded to account for a series of properties and functional dynamics. In the neurobiological context, communities may indicate brain regions that are involved in one same activity, representing neural segregated processes. Several studies have demonstrated the modular character of organization of brain activities. However, empirical evidences regarding to its dynamics and relation to different levels of consciousness have not been reported yet. Within this context, this research sought to characterize the community structure of functional brain networks during an anesthetic induction process. The experiment was based on intra-cranial recordings of neural activities of an old world macaque of the species Macaca fuscata during a Ketamine-Medetomidine anesthetic induction process. Networks were serially estimated in time intervals of five seconds. Changes were observed within about one and a half minutes after the administration of the anesthetics, revealing the occurrence of a transition on the community structure. The awake state was characterized by the presence of large clusters involving frontal and parietal regions, while the anesthetized state by the presence of communities in the primary visual and motor cortices, being the areas of the secondary associative cortex most affected. The results report the influence of general anesthesia on the structure of functional clusters, contributing for understanding some new aspects of neural correlates of consciousness.Comment: 24 pages, 8 figures. arXiv admin note: text overlap with arXiv:1604.0000

Double Dissociation of Format-Dependent and Number-Specific Neurons in Human Parietal Cortex

Based on neuroimaging methods, it is a commonly held view that numerical representation in the human parietal lobes is format independent. We used a transcranial magnetic stimulation adaptation paradigm to examine the existence of functionally segregated overlapping populations of neurons for different numerical formats and to reveal how numerical information is encoded and represented. Based on 2 experiments, we found that right parietal lobe stimulation showed a dissociation between digits and verbal numbers, whereas the left parietal lobe showed a double dissociation between the different numerical formats. Further analysis and modeling also excluded pre- or postrepresentational components as the source of the current effects. These results demonstrate that both parietal lobes are equipped with format-dependent neurons that encode quantity

Anatomical and functional brain approach along short abrupt changes in G-levels

To conduct experiments under abrupt changes in g-levels, a single-engine aerobatic aircraft has been used, providing 6-8 seconds of reduced gravity, preceded and followed by 5-7 seconds of hypergravity periods. Due to the specific conditions of the flight and previous findings [1], the hypothesis of the present work lies on the idea that some sensory inputs could have a notorious effect on brain final responses when gravity is altered. Therefore, this study focuses on the evaluation of such hypothesis, based on the analysis of the evolution in time of intracranial activity of limbic, visual and auditory cortices. Five subjects (N=5, age 41¿14 years) have flown in parabolic flight with their eyes both open and closed. Electroencephalogram signals were recorded with an Emotive Epoc headset, synchronized with a triaxial accelerometer. The intracranial brain bioelectric activity (standardized current density) throughout the parabola, was calculated by applying Standard Low Resolution Brain Electromagnetic Tomography, and it was analyzed for the limbic, visual and auditory cortices. Intracranial activity of the Temporal, Parietal and Occipital lobes were carried out as well in order to compare the different periods/phases of the flight. Results detected a lower brain activity during the hypogravity phase in all lobes and cortices, only in the case of open eyes. The bioelectrical brain activity along the parabola showed similar patterns in all lobes and cortices, when visual inputs are highlighted. Suppressing the sight, two major behaviors were detected in brain activity: one for temporal lobe and auditory cortex, and second one for the rest of the lobes and visual cortex. It Seemed that, flying with closed eyes, other sensory stimuli were enhanced, in this case the auditory cortex. To confirm the validity of the results two-way ANOVA (factors lobe/phases) and Fisher post hoc test have been applied on mean intracranial activity values in all cases. Spectral entropy evolution in time has been considered as a fast indicator of the sudden extracranial brain activity variation during short g-changes. For open eyes, spectral entropy values indicated a slight decrease at the onset of the hypogravity phase, whereas in case of closed eyes, this change was detected in the last seconds of the parabola, even though these fluctuations were statistically non-significant. Results suggest that some of the sensory inputs can indeed have an impact on brain final response, when gravity conditions are altered.Peer ReviewedPostprint (published version