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.

Functional MRI of apomorphine activation of the basal ganglia in awake rhesus monkeys.

Purpose

To estimate the relationship between R2 = 1/T2 as measured with a double echo spin echo sequence and total iron concentration in gray matter structures in the brains of aging rhesus monkeys.



Materials and Methods

Using a 1.5-T magnetic resonance (MR) imager, we collected double echo spin echo images of the brains of 12 female rhesus monkeys aged between 9 and 23 years. From the double echo images, the transverse relaxation rate R2 = 1/T2 was calculated in selected gray matter regions. After the animals were euthanized, their brains were excised and tissue punches were taken of the substantia nigra, globus pallidus, and gray matter regions of the cerebellum. Some of the tissue punches were assayed for total iron using atomic absorption spectroscopy.



Results

The range of tissue iron concentration spanned from 15 to 450 μg/g wet weight, with the highest levels in the globus pallidus and the lowest levels in the cerebellum. The results show that R2 was highly correlated with the total iron concentration and that the relationship between R2 and tissue iron concentration appeared to depend upon the iron concentration. For concentrations above approximately 150 μg/g wet weight, R2 increased with a sensitivity of 0.0484 ± 0.0023 second−1(μg/g)−1. In contrast, where the iron concentration was below 150 μg/g, R2 increased at 0.0013 ± 0.0073 second−1(μg/g)−1. The bilinear behavior may reflect changes with age in the relative amounts of iron distributed diffusely and in granular form in the globus pallidus and substantia nigra. Histological sections of the tissues stained for iron and ferritin support this hypothesis and indicate that the distribution of ferritin is similar to the distribution of iron.



Conclusion

This study reaffirms the value of measuring the MR relaxation rate R2 for a noninvasive estimate of iron content in the brain and identified limitations in the relationship at low tissue iron concentrations. J. Magn. Reson. Imaging 2005;21:118–127. © 2005 Wiley-Liss, Inc.

Correlation of R2 with total iron concentration in the brains of rhesus monkeys.

Background: HIV dementia is a form of subcortical dementia Clinical, radiologic, pathologic, and biochemical studies suggest a major contribution of basal ganglia dysfunction to the pathogenesis of this disorder Many investigators have proposed a contribution of a disrupted blood–brain barrier (BBB) to the pathogenesis of HIV dementia Objective: To identify microvascular abnormalities in vivo in basal ganglia or white matter of persons with HIV dementia Methods: Time course of MRI postcontrast enhancement was determined in basal ganglia and white matter of HIV-infected persons without dementia (Memorial Sloan Kettering [MSK] score of 0; n = 4); HIV-infected persons with mild dementia (MSK score of 05; n = 2); and HIV-infected persons with moderate-to-severe dementia (MSK ≥ 10; n = 6) Results: Increased basal ganglia enhancement was observed in individuals with moderate-to-severe dementia relative to nondemented individuals, both immediately and 30 minutes after contrast administration Decline of basal ganglia enhancement was slower in the moderately to severely demented patients and, when normalized to intravascular enhancement of sagittal sinus, suggested leakage of contrast agent, consistent with increased permeability of BBB A significant correlation between the postcontrast fractional enhancement at 30 minutes (FE30) and the MSK score was noted White matter showed no significant differences in postcontrast enhancement among the three groups Conclusion: Increased early enhancement in basal ganglia of the HIV dementia group is consistent with increased regional cerebral blood volume (rCBV) Increased late enhancement is strongly suggestive of BBB disruption Similar abnormalities were absent in the white matter adjacent to the caudate nucleus

Cerebrovascular changes in the basal ganglia with HIV dementia

Motor slowing is a universal feature of human aging, and parkinsonian signs are commonly expressed in human senescence. In the present study, age-associated declines in motor functions in 31 female rhesus monkeys were quantified by activity monitors and an automated test panel, and the incidence of parkinsonian signs was scored using a movement dysfunction assessment scale. Activity levels in middle-aged monkeys (12-17 years old) were less than half that of young animals (5-8 years old) and were further depressed in aged monkeys (21-27 years old). Movement dysfunction scores increased significantly with increasing age. Two or more parkinsonian signs were exhibited by 20% of the middle-aged monkeys and 36% of the aged monkeys. Slowing performance times on fine-motor hand tasks correlated significantly with increasing age. Motor learning was seen in all age groups, but improved faster in the young monkeys. The data suggest that aging rhesus monkeys provide an appropriate model to analyze the biological processes leading to motor slowing and the expression of parkinsonian signs in human senescence.

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Motor Slowing and Parkinsonian Signs in Aging Rhesus Monkeys Mirror Human Aging

OBJECTIVE To identify blinking-induced functional magnetic resonance imaging (fMRI) activation patterns in five benign essential blepharospasm (BEB) patients and five age-matched control subjects. METHODS fMRI brain activation maps were obtained during repeated conditions of spontaneous and voluntary blinking in BEB and control groups. Blood oxygen level-dependent intensity images were collected from two separate runs as 16 axial and 16 coronal, 8 mm thick slices using a T2-star weighted gradient echo EPI sequence, coregistered with anatomic images. Spatially normalized and isotropically blurred activation maps for each subject were combined within groups of BEB patients and control subjects to generate maps of the intersubject mean fractional signal change.RESULTS Substantially greater activation during spontaneous and voluntary blinking was seen in BEB patients compared with control subjects in the anterior visual cortex, anterior cingulate cortex, primary motor cortex, central region of the thalamus, and superior cerebellum. In both groups, activations were generally greater for voluntary than for spontaneous blinking. CONCLUSIONS The activations observed might represent a hyperactive cortical circuit linking visual cortex, limbic system, supplementary motor cortex, cerebellum, and supranuclear motor pathways innervating the periorbital muscles.

Anders H. Andersen

Papers

Functional MRI of apomorphine activation of the basal ganglia in awake rhesus monkeys.

Correlation of R2 with total iron concentration in the brains of rhesus monkeys.

Cerebrovascular changes in the basal ganglia with HIV dementia

Motor Slowing and Parkinsonian Signs in Aging Rhesus Monkeys Mirror Human Aging

A functional magnetic resonance imaging study in patients with benign essential blepharospasm.