1,364 research outputs found
Transcranial magnetic stimulation, causal structure-function mapping and networks of functional relevance
No full textTranscranial magnetic stimulation is now a well-established tool for inducing transient changes in brain activity non-invasively in conscious human volunteers. During the past couple of years, the ability to actively interfere with neural processing during behavioral performance has been used increasingly for the investigation of causal brain-behavior relationships in higher cognitive functions. The simultaneous combination of transcranial magnetic stimulation with methods of functional brain imaging, however, promises to be of especially great value for our understanding of the human brain, as it provides the opportunity to stimulate brain circuits while simultaneously monitoring changes in brain activity and behavior. Such an approach could help us to identify brain networks of functional relevance, and might enable causal brain-behavior inferences across the entire brain
Parietal cortex and spatial cognition
No full textThe parietal cortex consists of several prominent anatomical regions in the posterior part of the human brain. Although very heterogeneous stimuli and tasks activate parietal brain regions, a large body of empirical evidence points to a particular role of the posterior parietal cortex in spatial cognition. This article aims at providing a comprised overview regarding the existing evidence on the functional architecture of posterior parietal cortex and its relation to spatial cognition abilities. The article summarizes and systematically compares evidence from lesion, human functional brain imaging, and human functional brain interference studies, providing the whole range from early neuropsychological insights to latest state-of-the-art multimodal functional imaging and multivariate brain connectivity approaches. As for this latter type of evidence, the article outlines in more detail how our group has recently applied: (i) combined TMS & fMRI, (ii) data-driven multivariate fMRI, and (iii) effective brain connectivity analyses in order to functionally segregate the specific contribution of various parietal sub-regions for particular spatial sub-functions. Based on these recent findings, it is proposed that we are now at the verge of applying these new analytical frameworks in human functional brain imaging in order to functionally fractionate brain regions which are conventionally modelled as functional units, e.g. areas within the posterior parietal cortex, into distinct subdivisions with different functional contributions
Using non-invasive brain interference as a tool for mimicking spatial neglect in healthy volunteers.
No full textVisuospatial processing refers to the spatial perception, recognition and analysis of visual input. Human functional brain imaging studies have consistently revealed the involvement of fronto-parietal brain areas during the execution of visuospatial tasks. Just as the execution of these tasks activates fronto-parietal regions in the healthy brain, lesions to those structures, e.g. after stroke or brain injury, cause specific spatial deficits. The most prominent of these is known as spatial neglect. There are several competing theories on the neural mechanisms underlying spatial neglect. Although each of these theories postulates different underlying physiological mechanisms, they all account in their own way for the fact that the prevalence of neglect is much higher following right hemisphere lesions. This makes it difficult to distinguish between the different models at a behavioural level. Until today, it was impossible to empirically address these matters and to provide direct and conclusive empirical evidence in favour of one of the competing theories of spatial neglect. This review article describes the neural correlates of intact visuospatial processing as revealed by non-invasive functional brain imaging studies. It subsequently focuses on the approach of using the non-invasive brain inference technique of transcranial magnetic brain stimulation (TMS) to transiently and reversibly disrupt neural activity in these visuospatial processing-related brain regions. Using this approach, we can now imitate specific spatial deficits and neglect-like symptoms in healthy volunteers. Mimicking and manipulating the spatial deficits following unilateral brain lesions, under controlled experimental conditions, may allow for the development of new therapeutic interventions for parietal stroke patients suffering from real spatial neglect. The perspective is to use non-invasive brain interference to guide and promote functional recovery on a brain-system level in stroke and neglect patients, based on knowledge directly derived from fundamental brain research in healthy volunteers
Tracking the mind's image in the brain: Combining evidence from fMRI and rTMS: a multi-methodological approach to the experimental investigation of functional brain-behavior-relationships in the domain of visuospatial processing and visual imagery.
No full textToponymical lexics in the pre-war period of A.T. Tvardovskiy’s creative work
No full textThe pre-war period (1926-1940) of A.T. Tvaedovskiy’s creative work, the great poet of the 20yh century, born in the Smolensk Region, is a period of his rising as an insuperable master of word, a people’s tribune, the time when the main traits of his poetry were developed and when his formation as a founder of the Smolensk Poetic School occurred. One of the central themes of the SPS poets, and first of all, A.T. Tvardovskiy himself, was the theme of “the minor” and “the big”. Motherland, which was materialized in significant motives through a system of toponyms. i.e. the names of geograpphical places. The article analyzes a system of macro- and mictrotoponyms and demonstrates their part in revealing of the thematical content of numerous pre-war poems (A Trip to Zagorye, 1939, Station Pochinok, 1936, and others), as well the first epical poem of the author Strana Muraviya (1936)
The hybrid model of attentional control : new insights into hemispheric asymmetries inferred from TMS research
Full text linkSeveral competing theories on the mechanisms underlying attentional control have emerged over the years that, despite their substantial differences, all emphasize the importance of hemispheric asymmetries. Transcranial magnetic stimulation (TMS) has proven particularly successful in teasing them apart by selective perturbation of the dorsal and ventral fronto-parietal network. We here critically review the TMS literature and show that hemispheric asymmetries within the dorsal attention network differ between parietal and frontal cortex. Specifically, posterior parietal cortex seems to be characterized by a contralateral bias of each hemisphere and competition between them. In contrast, the right frontal eye field seems to be involved in shifting attention toward both hemifields, whereas left frontal eye field is only involved on shifting attention toward the contralateral hemifield. In the light of presented evidence, we propose to revise the functional-anatomical model originally proposed by Corbetta and Shulman (2011, 2001) and introduce a hybrid model of hemispheric asymmetries in attentional control
Combining TMS and functional imaging in cognitive brain research: Possibilities and limitations
No full textTranscranial magnetic stimulation (TMS) is a widely used tool for the non-invasive study of basic neurophysiological processes and the relationship between brain and behavior. We review the physical and physiological background of TMS and discuss the large body of perceptual and cognitive studies, mainly in the visual domain, that have been performed with TMS in the past 15 years. We compare TMS with other neurophysiological and neuropsychological research tools and propose that TMS, compared with the classical neuropsychological lesion studies, can make its own unique contribution. As the main focus of this review, we describe the different approaches of combining TMS with functional neuroimaging techniques. We also discuss important shortcomings of TMS, especially the limited knowledge concerning its physiological effects, which often make the interpretation of TMS results ambiguous. We conclude with a critical analysis of the resulting conceptual and methodological limitations that the investigation of functional brain-behavior relationships still has to face. We argue that while some of the methodological limitations of TMS applied alone can be overcome by combination with functional neuroimaging, others will persist until its physical and physiological effects can be controlled
Dissecting hemisphere-specific contributions to visual spatial imagery using parametric brain mapping
No full textIn the current study we aimed to empirically test previously proposed accounts of a division of labour between the left and right posterior parietal cortices during visuospatial mental imagery. The representation of mental images in the brain has been a topic of debate for several decades. Although the posterior parietal cortex is involved bilaterally, previous studies have postulated that hemispheric specialisation might result in a division of labour between the left and right parietal cortices. In the current fMRI study, we used an elaborated version of a behaviourally-controlled spatial imagery paradigm, the mental clock task, which involves mental image generation and a subsequent spatial comparison between two angles. By systematically varying the difference between the two angles that are mentally compared, we induced a symbolic distance effect: smaller differences between the two angles result in higher task difficulty. We employed parametrically weighed brain imaging to reveal brain areas showing a graded activation pattern in accordance with the induced distance effect. The parametric difficulty manipulation influenced behavioural data and brain activation patterns in a similar matter. Moreover, since this difficulty manipulation only starts to play a role from the angle comparison phase onwards, it allows for a top-down dissociation between the initial mental image formation, and the subsequent angle comparison phase of the spatial imagery task. Employing parametrically weighed fMRI analysis enabled us to top-down disentangle brain activation related to mental image formation, and activation reflecting spatial angle comparison. The results provide first empirical evidence for the repeatedly proposed division of labour between the left and right posterior parietal cortices during spatial imagery. (C) 2014 Elsevier Inc. All rights reserved
The default mode network and the working memory network are not anti-correlated during all phases of a working memory task.
Full text linkIntroductionThe default mode network and the working memory network are known to be anti-correlated during sustained cognitive processing, in a load-dependent manner. We hypothesized that functional connectivity among nodes of the two networks could be dynamically modulated by task phases across time.MethodsTo address the dynamic links between default mode network and the working memory network, we used a delayed visuo-spatial working memory paradigm, which allowed us to separate three different phases of working memory (encoding, maintenance, and retrieval), and analyzed the functional connectivity during each phase within and between the default mode network and the working memory network networks.ResultsWe found that the two networks are anti-correlated only during the maintenance phase of working memory, i.e. when attention is focused on a memorized stimulus in the absence of external input. Conversely, during the encoding and retrieval phases, when the external stimulation is present, the default mode network is positively coupled with the working memory network, suggesting the existence of a dynamically switching of functional connectivity between "task-positive" and "task-negative" brain networks.ConclusionsOur results demonstrate that the well-established dichotomy of the human brain (anti-correlated networks during rest and balanced activation-deactivation during cognition) has a more nuanced organization than previously thought and engages in different patterns of correlation and anti-correlation during specific sub-phases of a cognitive task. This nuanced organization reinforces the hypothesis of a direct involvement of the default mode network in cognitive functions, as represented by a dynamic rather than static interaction with specific task-positive networks, such as the working memory network
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