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Síntese,modelagem e simulação de estruturas neurais morfologicamente realísticas.; Synthesis, Modeling and Simulation of morphologically realistic neural simulation.

Coelho, Regina Célia
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 25/09/1998 Português
Relevância na Pesquisa
46.19%
Os aspectos morfológicos dos neurônios e estruturas neurais, embora potencialmente importantes, têm recebido relativamente pouca atenção na literatura em neurociência. Este trabalho consiste numa substancial parte de um projeto em desenvolvimento no Grupo de Pesquisa em Visão Cibernética voltado para o estudo da relação formal/função neural. Mais especificamente, o presente trabalho dedica particular atenção para a síntese, modelagem e simulação de estruturas neurais morfologicamente realísticas. A tese se inicia com revisões bibliográficas sobre visão biológica e neurociência, direcionadas aos assuntos a serem aqui abordados. Começamos a descrição dos desenvolvimentos com um levantamento, avaliação e proposta de medidas neuromorfométricas adequadas para exprimir as propriedades mais representativas para nosso trabalho, tais como cobertura espacial, complexidade e decaimento eletrônico. Incluímos nessa parte a metodologia utilizada para a geração de neurônios artificiais bidimensionais estatisticamente semelhantes aos naturais. Apresenta-se também a extensão desta metodologia para o caso tridimensional, validada pela análise neuroinorfométrica dos neurônios gerados. Na seqüência, descrevemos o processo de geração de estruturas neurais compostas de neurônios. Considerando modelos com uma camada neural para a codificação de especificidade de orientação...

Exercise and Training to Optimize Functional Motor Performance in Stroke: Driving Neural Reorganization?

Shepherd, Roberta B.
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
Publicado em //2001 Português
Relevância na Pesquisa
36.02%
Neurorehabilitation is increasingly taking account of scientific findings. Research areas directing stroke rehabilitation are neurophysiology; adaptability to use and activity; biomechanics; skill learning; and exercise science (task, context specificity). Understanding impairments and adaptations enables a reappraisal of interventions—for example,changes in motor control resulting from impairments (decreased descending inputs, reduced motor unit synchronization), secondary soft tissue changes (muscle length and stiffness changes) are adaptations to lesion and disuse. Changes in interventions include increasing emphasis on active exercise and task-specific training, active and passive methods of preserving muscle extensibility. Training has the potential to drive brain reorganization and to optimize functional performance. Research drives the development of training programs, and therapists are relying less on one-to-one, hands-on service delivery, making use of circuit training and group exercise and of technological advances (interactive computerized systems, treadmills) which increase time spent in active practice, Emphasis is on skill training, stressing cognitive engagement and practice, aiming to increase strength, control...

Reorganization of Functional Brain Maps After Exercise Training: Importance of Cerebellar-Thalamic-Cortical Pathway

Holschneider, DP; Yang, J; Guo, Y; Maarek, J-M I
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.02%
Exercise training (ET) causes functional and morphologic changes in normal and injured brain. While studies have examined effects of short-term (same day) training on functional brain activation, less work has evaluated effects of long-term training, in particular treadmill running. An improved understanding is relevant as changes in neural reorganization typically require days to weeks, and treadmill training is a component of many neurorehabilitation programs.

Human Adult Cortical Reorganization and Consequent Visual Distortion

Dilks, Daniel D.; Serences, John T.; Rosenau, Benjamin J.; Yantis, Steven; McCloskey, Michael
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 05/09/2007 Português
Relevância na Pesquisa
26.48%
Neural and behavioral evidence for cortical reorganization in the adult somatosensory system after loss of sensory input (e.g., amputation) has been well documented. In contrast, evidence for reorganization in the adult visual system is far less clear: neural evidence is the subject of controversy, behavioral evidence is sparse, and studies combining neural and behavioral evidence have not previously been reported. Here, we report converging behavioral and neuroimaging evidence from a stroke patient (B.L.) in support of cortical reorganization in the adult human visual system. B.L.’s stroke spared the primary visual cortex (V1), but destroyed fibers that normally provide input to V1 from the upper left visual field (LVF). As a consequence, B.L. is blind in the upper LVF, and exhibits distorted perception in the lower LVF: stimuli appear vertically elongated, toward and into the blind upper LVF. For example, a square presented in the lower LVF is perceived as a rectangle extending upward. We hypothesized that the perceptual distortion was a consequence of cortical reorganization in V1. Extensive behavioral testing supported our hypothesis, and functional magnetic resonance imaging (fMRI) confirmed V1 reorganization. Together, the behavioral and fMRI data show that loss of input to V1 after a stroke leads to cortical reorganization in the adult human visual system...

Growth-related neural reorganization and the autism phenotype: a test of the hypothesis that altered brain growth leads to altered connectivity

Lewis, John D.; Elman, Jeffrey L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/2008 Português
Relevância na Pesquisa
35.96%
Theoretical considerations, and findings from computational modeling, comparative neuroanatomy and developmental neuroscience, motivate the hypothesis that a deviant brain growth trajectory will lead to deviant patterns of change in cortico-cortical connectivity. Differences in brain size during development will alter the relative cost and effectiveness of short- and long-distance connections, and should thus impact the growth and retention of connections. Reduced brain size should favor long-distance connectivity; brain overgrowth should favor short-distance connectivity; and inconsistent deviations from the normal growth trajectory – as occurs in autism – should result in potentially disruptive changes to established patterns of functional and physical connectivity during development. To explore this hypothesis, neural networks which modeled inter-hemispheric interaction were grown at the rate of either typically developing children or children with autism. The influence of the length of the inter-hemispheric connections was analyzed at multiple developmental time-points. The networks that modeled autistic growth were less affected by removal of the inter-hemispheric connections than those that modeled normal growth – indicating a reduced reliance on long-distance connections – for short response times...

Non-fluent aphasia and neural reorganization after speech therapy: insights from human sleep electrophysiology and functional magnetic resonance imaging

Sarasso, S.; Santhanam, P.; Määtta, S.; Poryiazova, R.; Ferrarelli, F.; Tononi, G.; Small, S.L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/2010 Português
Relevância na Pesquisa
36.12%
Stroke is associated with long-term functional deficits. Behavioral interventions are often effective in promoting functional recovery and plastic changes. Recent studies in normal subjects have shown that sleep, and particularly slow wave activity (SWA), is tied to local brain plasticity and may be used as a sensitive marker of local cortical reorganization after stroke. In a pilot study, we assessed the local changes induced by a single exposure to a therapeutic session of IMITATE (Intensive Mouth Imitation and Talking for Aphasia Therapeutic Effects), a behavioral therapy used for recovery in patients with post-stroke aphasia. In addition, we measured brain activity changes with functional magnetic resonance imaging (fMRI) in a language observation task before, during and after the full IMITATE rehabilitative program. Speech production improved both after a single exposure and the full therapy program as measured by the Western Aphasia Battery Repetition subscale. We found that IMITATE induced reorganization in functionally connected speech-relevant areas in the left hemisphere. These preliminary results suggest that sleep hd-EEGs, and the topographical analysis of SWA parameters, is well suited to investigating brain plastic changes underpinning functional recovery in neurological disorders.

Compensatory Neural Reorganization in Tourette Syndrome

Jackson, Stephen R.; Parkinson, Amy; Jung, Jeyoung; Ryan, Suzanne E.; Morgan, Paul S.; Hollis, Chris; Jackson, Georgina M.
Fonte: Cell Press Publicador: Cell Press
Tipo: Artigo de Revista Científica
Publicado em 12/04/2011 Português
Relevância na Pesquisa
36.02%
Children with neurological disorders may follow unique developmental trajectories whereby they undergo compensatory neuroplastic changes in brain structure and function that help them gain control over their symptoms [1–6]. We used behavioral and brain imaging techniques to investigate this conjecture in children with Tourette syndrome (TS). Using a behavioral task that induces high levels of intermanual conflict, we show that individuals with TS exhibit enhanced control of motor output. Then, using structural (diffusion-weighted imaging) brain imaging techniques, we demonstrate widespread differences in the white matter (WM) microstructure of the TS brain that include alterations in the corpus callosum and forceps minor (FM) WM that significantly predict tic severity in TS. Most importantly, we show that task performance for the TS group (but not for controls) is strongly predicted by the WM microstructure of the FM pathways that lead to the prefrontal cortex and by the functional magnetic resonance imaging blood oxygen level-dependent response in prefrontal areas connected by these tracts. These results provide evidence for compensatory brain reorganization that may underlie the increased self-regulation mechanisms that have been hypothesized to bring about the control of tics during adolescence.

Patterns of brain reorganization subsequent to left fusiform damage: fMRI evidence from visual processing of words and pseudowords, faces and objects

Tsapkini, Kyrana; Vindiola, Manuel; Rapp, Brenda
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.41%
Little is known about the neural reorganization that takes place subsequent to lesions that affect orthographic processing (reading and/or spelling). We report on an fMRI investigation of an individual with a left mid-fusiform resection that affected both reading and spelling (Tsapkini & Rapp, 2010). To investigate possible patterns of functional reorganization, we compared the behavioral and neural activation patterns of this individual with those of a group of control participants for the tasks of silent reading of words and pseudowords and the passive viewing of faces and objects, all tasks that typically recruit the inferior temporal lobes. This comparison was carried out with methods that included a novel application of Mahalanobis distance statistics, and revealed: (1) normal behavioral and neural responses for face and object processing, (2) evidence of neural reorganization bilaterally in the posterior fusiform that supported normal performance in pseudoword reading and which contributed to word reading (3) evidence of abnormal recruitment of the bilateral anterior temporal lobes indicating compensatory (albeit insufficient) recruitment of mechanisms for circumventing the word reading deficit.

Experience-dependent neural plasticity in the adult damaged brain

Kerr, Abigail L.; Cheng, Shao-Ying; Jones, Theresa A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.4%
Behavioral experience is at work modifying the structure and function of the brain throughout the lifespan, but it has a particularly dramatic influence after brain injury. This review summarizes recent findings on the role of experience in reorganizing the adult damaged brain, with a focus on findings from rodent stroke models of chronic upper extremity (hand and arm) impairments. A prolonged and widespread process of repair and reorganization of surviving neural circuits is instigated by injury to the adult brain. When experience impacts these same neural circuits, it interacts with degenerative and regenerative cascades to shape neural reorganization and functional outcome. This is evident in the cortical plasticity resulting from compensatory reliance on the “good” forelimb in rats with unilateral sensorimotor cortical infarcts. Behavioral interventions (e.g., rehabilitative training) can drive functionally beneficial neural reorganization in the injured hemisphere. However, experience can have both behaviorally beneficial and detrimental effects. The interactions between experience-dependent and injury-induced neural plasticity are complex, time-dependent, and varied with age and other factors. A better understanding of these interactions is needed to understand how to optimize brain remodeling and functional outcome.

Age-related Neural Reorganization during Spoken Word Recognition: The Interaction of Form and Meaning

Shafto, Meredith; Randall, Billi; Stamatakis, Emmanuel A.; Wright, Paul; Tyler, L. K.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
46.41%
Research on language and aging typically shows that language comprehension is preserved across the life span. Recent neuroimaging results suggest that this good performance is underpinned by age-related neural reorganization [e.g., Tyler, L. K., Shafto, M. A., Randall, B., Wright, P., Marslen-Wilson, W. D., & Stamatakis, E. A. Preserving syntactic processing across the adult life span: The modulation of the frontotemporal language system in the context of age-related atrophy. Cerebral Cortex, 20, 352–364, 2010]. The current study examines how age-related reorganization affects the balance between component linguistic processes by manipulating semantic and phonological factors during spoken word recognition in younger and older adults. Participants in an fMRI study performed an auditory lexical decision task where words varied in their phonological and semantic properties as measured by degree of phonological competition and imageability. Older adults had a preserved lexicality effect, but compared with younger people, their behavioral sensitivity to phonological competition was reduced, as was competition-related activity in left inferior frontal gyrus. This was accompanied by increases in behavioral sensitivity to imageability and imageability-related activity in left middle temporal gyrus. These results support previous findings that neural compensation underpins preserved comprehension in aging and demonstrate that neural reorganization can affect the balance between semantic and phonological processing.

Diffusion tensor imaging (DTI) detects microstructural reorganization in the brain associated with chronic irritable bowel syndrome (IBS)

Ellingson, Benjamin M.; Mayer, Emeran; Harris, Robert J.; Ashe-McNally, Cody; Naliboff, Bruce D.; Labus, Jennifer S.; Tillisch, Kirsten
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.02%
Irritable bowel syndrome (IBS) is a common gastrointestinal disorder characterized by recurring abdominal pain associated with alterations in bowel habits. We hypothesized patients with chronic visceral pain associated with IBS may have microstructural differences in the brain compared with healthy control subjects (HCs), indicative of long-term neural reorganization of chronic pain pathways and regions associated with sensory integration. In the current study we performed population-based voxel-wise DTI comparisons and probabilistic tractography in a large sample of phenotyped patients with IBS (n=33) and HCs (n=93). Patients had lower fractional anisotropy (FA) in thalamic regions, the basal ganglia and sensory/motor association/integration regions as well as higher FA in frontal lobe regions and the corpus callosum. In addition, patients had reduced mean diffusivity (MD), within the globus pallidus, and higher MD in the thalamus, internal capsule, and coronal radiata projecting to sensory/motor regions, suggestive of differential changes in axon/dendritic density in these regions. Sex differences in FA and MD were also observed in the patients but not in HCs. Probabilistic tractography confirmed a higher degree of connectivity in patients between the thalamus and pre-frontal cortex...

Mechanisms of Neural Reorganization in Chronic Stroke Subjects after Virtual Reality Training

Saleh, S; Bagce, H; Qiu, Q; Fluet, G; Merians, A; Adamovich, S; Tunik, E
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2011 Português
Relevância na Pesquisa
36.15%
This study investigates patterns of brain reorganization in chronic stroke subjects after two weeks of robot-assisted arm and hand training in virtual reality (VR). Four subjects were studied with event-related fMRI while doing simple paretic hand finger movements before (double baseline) and after training. Bilateral hand movements were recorded and used to provide real-time feedback to subjects during scanning to eliminate performance confounds on fMRI results. The kinematic parameters of each movement were also used in the general linear model with the BOLD signal to investigate training-induced changes in neuromotor coupling. Univariate analysis showed an increase in BOLD signal in the ipsilesional hemisphere in two subjects and a decrease in activity in the other two subjects. Seed voxel based functional connectivity analysis revealed an increase in connectivity between ipsilesional motor cortex and bilateral sensorimotor cortex during finger movements in all four subjects. Hemispheric laterality index values showed a tendency to decrease reflecting a reduction in the over-dominance of the contralesional hemisphere. The study is novel in terms of 1) tracking finger movement during a motor task in the scanner, 2) monitoring motor performance during the experiment and 3) giving online visual feedback of subjects’ movement. This pilot study introduces a novel approach to study neural plasticity by combining measures of regional intensity...

Functional magnetic resonance imaging evaluation of brain function reorganization in cerebral stroke patients after constraint-induced movement therapy★

Zhao, Jun; Zhang, Tong; Xu, Jianmin; Wang, Mingli; Zhao, Shengjie
Fonte: Medknow Publications & Media Pvt Ltd Publicador: Medknow Publications & Media Pvt Ltd
Tipo: Artigo de Revista Científica
Publicado em 25/05/2012 Português
Relevância na Pesquisa
36.12%
In this study, stroke patients received constraint-induced movement therapy for 3 weeks. Before and after constraint-induced movement therapy, the flexibility of their upper limbs on the affected side was assessed using the Wolf motor function test, and daily use of their affected limbs was assessed using the movement activities log, and cerebral functional reorganization was assessed by functional magnetic resonance imaging. The Wolf motor function test score and the movement activities log quantity and quality scores were significantly increased, while action performance time in the Wolf motor function test was significantly decreased after constraint-induced movement therapy. By functional magnetic resonance imaging examination, only scattered activation points were visible on the affected side before therapy. In contrast, the volume of the activated area was increased after therapy. The activation volume in the sensorimotor area was significantly different before and after therapy, and the activation area increased and appeared adjusted. In addition to the activated area around the lesions being decreased, there were also some new activated areas, including the supplementary movement area, premotor area and the ipsilateral sensorimotor area. Our findings indicate that constraint-induced movement therapy significantly improves the movement ability and daily use of the affected upper limbs in stroke patients and promotes cerebral functional reorganization.

Reorganization of the human motor cortex by sensory signals: A selective review

Miles, T.
Fonte: Blackwell Publishing Asia Publicador: Blackwell Publishing Asia
Tipo: Artigo de Revista Científica
Publicado em //2005 Português
Relevância na Pesquisa
36.02%
1. The normal human motor cortex can be made to reorganize by repeated stimulation of proprioceptive inputs, with or without concurrent stimulation of the motor cortex by transcranial magnetic nerve stimulation. Appropriate stimulation induces a focal increase in the excitability of corticospinal projections to specific muscles and, possibly, an increase in the area of the cortex projecting to those muscles. 2. We have shown that repeated stimulation on several successive days causes this ‘plastic’ reorganization to persist for at least several days. We have also used this approach to determine whether increases in the excitability of the motor cortex can be induced in stroke patients (in whom cortical excitability is usually depressed) and whether this is accompanied by functional changes. 3. The results of these studies were mixed but, in patients in whom plastic changes were induced, there were improvements and sometimes marked improvements in both motor function and some electrophysiological parameters. The reasons for the inconsistent results are not clear, but do not appear to relate to the site, size or nature of the lesion.; Timothy S Miles; The definitive version is available at www.blackwell-synergy.com

Phantomschmerz und kortikale Reorganisation: praeventive und therapeutische Effekte eines NMDA-Antagonisten; Phantom limb pain and cortical reorganization: preventive and therapeutical effects of an NMDA-antagonist

Wiech, Katja
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
Português
Relevância na Pesquisa
36.25%
Nach Amputation einer Extremität treten bei vielen Patienten Phantomschmerzen (PS) auf. Grundlage dieser Schmerzen ist eine Sensibilisierung schmerzrelevanter Strukturen, an der NMDA-Rezeptoren beteiligt sind. In der vorliegenden Studie wurde der analgetische Effekt eines NMDA-Antagonisten auf chronische PS sowie eine mögliche präventive Wirkung bei akuten Patienten untersucht. In beiden Teilstudien wurde der NMDA-Antagonist Memantine über 4 Wochen eingenommen und doppelblind gegen ein Plazebopräparat getestet. Bei Patienten mit chronischem PS tritt unter Memantine keine Schmerzreduktion ein. In der Präventionsstudie berichten dagegen die Patienten, die zusätzlich zum NMDA-Antagonisten über 7 Tage eine Regionalanästhesie erhielten, weniger PS als die Vergleichsgruppe, die mit einer Kombination aus Regionalanästhesie und Plazebopräparat versorgt wurde. In der Gesamtgruppe der akuten Patienten zeigte sich, daß die Prävention umso erfolgreicher ist, je früher nach der Amputation die Behandlung beginnt. In vorherigen Studien variierte die Phantomschmerzintensität mit einer Reorganisation im primären somatosensorischen Kortex. Bei den chronischen Patienten der vorliegenden Studie verstärkt sich diese kortikale Reorganisation (kR) unter der Einnahme von Memantine. Die Zunahme tritt unabhängig von Veränderungen der Schmerzintensität auf. Bei den akuten Patienten unterscheiden sich die Personen...

Investigation of the dorsal stream hypothesis in Williams syndrome

Bernardino, Inês
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
26.48%
O Síndrome de Williams (SW) é uma perturbação genética rara do neurodesenvolvimento caracterizada por alterações sensoriais, cognitivas e neuroanatómicas. Esta patologia constitui, por isso, um modelo ímpar para investigar a natureza modular (ou não) dos processos cognitivos, dado que proporciona uma oportunidade rara de estudo das relações entre genes, cérebro e comportamento. O SW tem suscitado interesse no domínio das neurociências cognitivas, devido ao seu perfil cognitivo peculiar, caracterizado por funções preservadas no domínio da linguagem e do reconhecimento facial em oposição a consideráveis défices de coerência visual e de perceção visuo-espacial. No SW verifica-se um viés a favor do processamento visual local, falhando ao mesmo tempo na integração desta informação local que é determinante para a perceção de coerência global. Estas dissociações funcionais no domínio cognitivo têm sido estudadas a par com dissociações ao nível do funcionamento neuronal particularmente no que diz respeito às vias de processamento visual dorsal e ventral. Contudo, o debate persiste e os correlatos neuroanatómicos e neurofisiológicos destes défices não estão ainda estabelecidos. O foco desta tese prende-se com a investigação de múltiplos níveis de processamento visual associados às vias dorsal e ventral no SW...

Dynamique cérébrale et réserve cognitive en situation d’attention sélective dans le vieillissement normal et les troubles de la cognition : approche neurofonctionnelle

Jennyfer, Ansado
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
Português
Relevância na Pesquisa
26.63%
La survenue de modifications cérébrales issues du vieillissement normal ou provoquées par la maladie d’Alzheimer entraîne un certain bouleversement de l’attention visuelle sélective, soit la capacité à centrer volontairement les mécanismes de perception sur un stimulus particulier en négligeant les stimuli non pertinents. A ces modifications viennent s’ajouter des phénomènes de réorganisations cérébrales qui peuvent s’illustrer sur l’axe inter-hémisphérique par une réduction de la latéralisation cérébrale dans le vieillissement normal et sur l’axe intra-hémisphérique par un accroissement de l’engagement des régions frontales et préfrontales dans le vieillissement normal et la maladie d’Alzheimer. Toutefois, les mécanismes sur lesquels reposent ces phénomènes de réorganisations cérébrales dans le vieillissement normal et la maladie d’Alzheimer dans le contexte de l’attention visuelle restent peu compris. Ce travail de thèse s’intéresse à la nature de la réorganisation cérébrale dans le vieillissement normal (inter-hémisphérique vs. intra-hémisphérique) en condition d’attention visuelle sélective et s’inscrit dans le modèle de la réserve cognitive afin de préciser la nature des mécanismes sous-jacents de la réorganisation cérébrale (réserve neurale vs. compensation neurale). Concernant la maladie d’Alzheimer...

Irreversible reorganization in a supercooled liquid originates from localised soft modes

Widmer-Cooper, Asaph; Perry, Heidi; Harrowell, Peter; Reichman, David R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/01/2009 Português
Relevância na Pesquisa
36.12%
The transition of a fluid to a rigid glass upon cooling is a common route of transformation from liquid to solid that embodies the most poorly understood features of both phases1,2,3. From the liquid perspective, the puzzle is to understand stress relaxation in the disordered state. From the perspective of solids, the challenge is to extend our description of structure and its mechanical consequences to materials without long range order. Using computer simulations, we show that the localized low frequency normal modes of a configuration in a supercooled liquid are causally correlated to the irreversible structural reorganization of the particles within that configuration. We also demonstrate that the spatial distribution of these soft local modes can persist in spite of significant particle reorganization. The consequence of these two results is that it is now feasible to construct a theory of relaxation length scales in glass-forming liquids without recourse to dynamics and to explicitly relate molecular properties to their collective relaxation.; Comment: Published online: 20 July 2008 | doi:10.1038/nphys1025 Available from http://www.nature.com/nphys/journal/v4/n9/abs/nphys1025.html

Universal Attractors of Reversible Aggregate-Reorganization Processes

Grosskinsky, Stefan; Timme, Marc; Naundorf, Bjoern
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.18%
We analyze a general class of reversible aggregate-reorganization processes. These processes are shown to exhibit globally attracting equilibrium distributions, which are \textit{universal}, i.e. identical for large classes of models. Furthermore, the analysis implies that for studies of equilibrium properties of \textit{any} such process, computationally expensive reorganization dynamics such as random walks can be replaced by more efficient, yet simpler methods. As a particular application, our results explain the recent observation of the formation of similar fractal aggregates from different initial structures by diffusive reorganization [Filoche and Sapoval, Phys. Rev. Lett. 85, 5118 (2000)].; Comment: 4 pages, 3 figures

Neural changes associated with semantic processing in healthy aging despite intact behavioral performance

Lacombe, Jacinthe; Jolicoeur, Pierre; Grimault, Stephan; Pineault, Jessica; Joubert, Sven
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
46.03%
Semantic memory recruits an extensive neural network including the left inferior prefrontal cortex (IPC) and the left temporoparietal region, which are involved in semantic control processes, as well as the anterior temporal lobe region (ATL) which is considered to be involved in processing semantic information at a central level. However, little is known about the underlying neuronal integrity of the semantic network in normal aging. Young and older healthy adults carried out a semantic judgment task while their cortical activity was recorded using magnetoencephalography (MEG). Despite equivalent behavioral performance, young adults activated the left IPC to a greater extent than older adults, while the latter group recruited the temporoparietal region bilaterally and the left ATL to a greater extent than younger adults. Results indicate that significant neuronal changes occur in normal aging, mainly in regions underlying semantic control processes, despite an apparent stability in performance at the behavioral level.