Co-Planar Stereotaxic Atlas of the Human Brain—3-Dimensional Proportional System: An Approach to Cerebral Imaging, J. Talairach, P. Tournoux. Georg Thieme Verlag, New York (1988), 122 pp., 130 figs. DM 268

This survey provides an overview of higher-order tensor decompositions, their applications, and available software. A tensor is a multidimensional or $N$-way array. Decompositions of higher-order tensors (i.e., $N$-way arrays with $N \geq 3$) have applications in psycho-metrics, chemometrics, signal processing, numerical linear algebra, computer vision, numerical analysis, data mining, neuroscience, graph analysis, and elsewhere. Two particular tensor decompositions can be considered to be higher-order extensions of the matrix singular value decomposition: CANDECOMP/PARAFAC (CP) decomposes a tensor as a sum of rank-one tensors, and the Tucker decomposition is a higher-order form of principal component analysis. There are many other tensor decompositions, including INDSCAL, PARAFAC2, CANDELINC, DEDICOM, and PARATUCK2 as well as nonnegative variants of all of the above. The N-way Toolbox, Tensor Toolbox, and Multilinear Engine are examples of software packages for working with tensors.

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Tensor Decompositions and Applications

The Blood-Brain Barrier in Health and Chronic Neurodegenerative Disorders

The neurovascular unit (NVU) comprises brain endothelial cells, pericytes or vascular smooth muscle cells, glia and neurons. The NVU controls blood-brain barrier (BBB) permeability and cerebral blood flow, and maintains the chemical composition of the neuronal 'milieu', which is required for proper functioning of neuronal circuits. Recent evidence indicates that BBB dysfunction is associated with the accumulation of several vasculotoxic and neurotoxic molecules within brain parenchyma, a reduction in cerebral blood flow, and hypoxia. Together, these vascular-derived insults might initiate and/or contribute to neuronal degeneration. This article examines mechanisms of BBB dysfunction in neurodegenerative disorders, notably Alzheimer's disease, and highlights therapeutic opportunities relating to these neurovascular deficits.

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Neurovascular pathways to neurodegeneration in Alzheimer's disease and other disorders.

Mr M, a patient with semantic dementia - a neurodegenerative disease that is characterized by the gradual deterioration of semantic memory - was being driven through the countryside to visit a friend and was able to remind his wife where to turn along the not-recently-travelled route. Then, pointing at the sheep in the field, he asked her "What are those things?" Prior to the onset of symptoms in his late 40s, this man had normal semantic memory. What has gone wrong in his brain to produce this dramatic and selective erosion of conceptual knowledge?

Where do you know what you know? The representation of semantic knowledge in the human brain.

Simultaneous algebraic reconstruction technique (SART): a superior implementation of the art algorithm.

Neural substrates of facial emotion processing using fMRI.

Behavioral research has demonstrated three major components of the lexical-semantic processing system: automatic activation of semantic representations, strategic retrieval of semantic representations, and inhibition of competitors. However, these component processes are inherently conflated in explicit lexical-semantic decision tasks typically used in functional magnetic resonance imaging (fMRI) research. Here, we combine the logic of behavioral priming studies and the neurophysiological phenomenon of fMRI priming to dissociate the neural bases of automatic and strategic lexical-semantic processes across a series of three studies. A single lexical decision task was used in all studies, with stimulus onset asynchrony or linguistic relationship between prime and target being manipulated. Study 1 demonstrated automatic semantic priming in the left mid-fusiform gyrus (mid-FFG) and strategic semantic priming in five regions: left middle temporal gyrus (MTG), bilateral anterior cingulate, anterior left inferior prefrontal cortex (aLIPC), and posterior LIPC (pLIPC). These priming effects were explored in more detail in two subsequent studies. Study 2 replicated the automatic priming effect in mid-FFG and demonstrated that automatic priming in this region is preferential for the semantic domain. Study 3 demonstrated a neural dissociation in regions contributing to the strategic semantic priming effect. Strategic semantic facilitation was observed in the aLIPC and MTG, whereas strategic semantic inhibition was observed in the pLIPC and anterior cingulate. These studies provide reproducible evidence for a neural dissociation between three well established components of the lexical-semantic processing system.

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Dissociation of Automatic and Strategic Lexical-Semantics: Functional Magnetic Resonance Imaging Evidence for Differing Roles of Multiple Frontotemporal Regions

The author presents an algebraic reconstruction technique (ART) as a viable alternative in computerized tomography (CT) from limited views. Recently, algorithms of iterative reconstruction-reprojection (IRR) based on the method of convolution-backprojection have been proposed for application in limited-view CT. Reprojection was used in an iterative fashion alternating with backprojection as a means of estimating projection values within the sector of missing views. In algebraic methods of reconstruction for CT, only those projections corresponding to known data are required. Reprojection along missing views would merely serve to introduce redundant equations. Computer simulation studies are presented which demonstrate significantly improved reconstructed images achieved by an ART algorithm as compared to IRR methods. >

Algebraic reconstruction in CT from limited views

The powerful trophic effects that glial cell line-derived neurotrophic factor (GDNF) exerts on midbrain dopamine neurones suggest its use in treating Parkinson's disease. However, some important questions remain about the possible therapeutic applications of GDNF. Here we demonstrate that the chronic infusion of 5 or 15 micro g/day GDNF into the lateral ventricle or the striatum, using programmable pumps, promotes restoration of the nigrostriatal dopaminergic system and significantly improves motor functions in rhesus monkeys with neural deficits modelling the terminal stages of Parkinson's disease. The functional improvements were associated with pronounced upregulation and regeneration of nigral dopamine neurones and their processes innervating the striatum. When compared with vehicle recipients, these functional improvements were associated with (i) >30% bilateral increase in nigral dopamine neurone cell size; (ii) >20% bilateral increase in the number of nigral cells expressing the dopamine marker tyrosine hydroxylase; (iii) >70 and >50% bilateral increase in dopamine metabolite levels in the striatum and the pallidum, respectively; (iv) 233 and 155% increase in dopamine levels in the periventricular striatal region and the globus pallidus, respectively, on the lesioned side; and (v) a five-fold increase in tyrosine hydroxylase-positive fibre density in the periventricular striatal region on the lesioned side. In addition, chronic GDNF treatment did not induce the side-effects generally associated with chronic administration of levodopa, the most widely used treatment for Parkinson's disease. Thus, the results suggest that the prolonged and controlled delivery of GDNF into the brain could be used to intervene in long-term neurodegenerative disease processes like Parkinson's disease. Additional studies are required to determine the potential differences between chronic, intraventricular and intraputamenal (or intranigral) delivery of GDNF to maximize the efficacy of infusion treatments.

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Anders H. Andersen

Papers

Simultaneous algebraic reconstruction technique (SART): a superior implementation of the art algorithm.

Neural substrates of facial emotion processing using fMRI.

Dissociation of Automatic and Strategic Lexical-Semantics: Functional Magnetic Resonance Imaging Evidence for Differing Roles of Multiple Frontotemporal Regions

Algebraic reconstruction in CT from limited views

Chronic, controlled GDNF infusion promotes structural and functional recovery in advanced parkinsonian monkeys