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The neural correlates of developmental dyslexia: a new meta-analysis of PET and fMRI activation studies
No full textINTRODUZIONE
Developmental dyslexia has been the focus of much functional anatomical research. The main trust of this work is that typical developmental dyslexics have a dysfunction of the phonological and orthography to phonology conversion systems, in which the left occipito-temporal cortex has a crucial role.
It remains to be seen whether there is a systematic co-occurrence of dysfunctional patterns of different functional systems perhaps converging on the same brain regions associated with the reading deficit. Such evidence would be relevant for theories like, for example, the magnocellular/attentional or the motor/cerebellar ones, which postulate a more basic and anatomically distributed disorder in dyslexia.
METODO
We addressed this issue with a meta-analysis of all the imaging literature published until September 2013 using a combination of hierarchical clustering and activation likelihood estimates.
RISULTATI
The clustering analysis on 2360 peaks identified 193 clusters, 92 of which proved significant for spatial extent. Following binomial tests on the clusters, we found a normal-control specific (i.e. reduced involvement in dyslexics) left hemispheric network involving the left inferior frontal, premotor, supramarginal cortices and the left infero-temporal and fusiform region: these were specific for reading and the visual-to-phonology processes. There was also a more dorsal left fronto-parietal network: these clusters included peaks from tasks involving phonological manipulation, but also motoric or visuo-spatial perception/attention. No cluster was identified in area V5 for no task. No significant effects were found for cerebellar clusters either.
CONCLUSIONI
We conclude that the available literature demonstrates a specific lack of activation of the left occipitotemporal cortex in dyslexics that is specific for reading and reading-like behaviours and for visuo-phonological tasks. Additional deficits may be associated with dorsal fronto-parietal deficits
The neural correlates of developmental dyslexia: a new meta-analysis of 48 neuroimaging studies
No full textOver the last two decades, developmental dyslexia has been the focus of much research using functional neuroimaging. A wide range of paradigms, tackling different neurocognitive domains, has been used to assess its neural correlates. The main trust of this work is that typical developmental dyslexics have dysfunction of the phonological and orthography to phonology conversion systems, normally housed in the left occipitotemporal cortex. It remains to be seen whether, besides this well replicated finding, there is a systematic co-occurrence of dysfunctional patterns of different functional systems perhaps converging on the same brain regions associated with the reading deficit. Such evidence would be relevant for theories of dyslexia like, for example, the magnocellular one. To address this problem, we performed a meta-analysis based on an optimized hierarchical clustering algorithm (Cattinelli et al., 2012) which automatically grouped 1982 activation peaks, extracted from 48 neuroimaging studies (fMRI and PET), into clusters in which the activation peaks had minimized spatial variance. The data was based on the literature published up to December 2011 including experiments on reading but also on phonological awareness, motor control, visual motion perception and so forth.
The clustering analysis identified 82 clusters. The functional role of the clusters was assessed on the basis of statistical criteria. In particular, the binomial test was used to identify which clusters showed a specific activation effect for dyslexics rather than for controls.
The left inferior parietal lobule, the left middle temporal gyrus, the left fusiform gyrus and the left cerebellum showed a specific association with the normal control groups, not being active in the dyslexics; on the other hand early subdivisions of visual cortices, bilaterally, the left insula and the right opercular portion of the inferior frontal gyrus showed a specific association with the dyslexic subjects.
A qualitative analysis of each cluster was also performed to evaluate the distribution of the activations peaks in relation to the experimental task (e.g. reading, phonological awareness, motor learning, visual motion discrimination, etc.).
We found that the aforementioned difference in left fusiform gyrus was selectively due to a lack of commitment to reading in adult dyslexics while the same region showed occasional activation for more basic visual tasks. On the other hand, the specific activation of early visual cortices in dyslexics was associated with a variety of visual tasks with reading tasks playing a major role.
We conclude that the available literature demonstrates a specific lack of activation of the left occipitotemporal cortex in dyslexics that is specific for reading and for visuo-phonological tasks. The larger early occipital activations in dyslexics may represent a compensatory effort for the visual analysis of printed words in the absence of a higher-level visual-word form neural expertise.
References
Cattinelli I., Borghese A.N., Gallucci M., Paulesu E. (In Press) Reading the reading brain: a new meta-analysis of functional imaging data of reading. J. Neurolinguistic
A meta-analysis of functional neuroimaging studies on developmental dyslexia across European orthographies: the ADOD model
Full text linkAccording to the “classic” and the “new” model, developmental dyslexia (DD) is associated with dysfunctions of the left temporoparietal (TP), ventral occipitotemporal (vOT) and frontal brain circuits. However, these models make different anatomo-functional predictions about the effects of age and orthographic depth on the neural correlates of DD. To test the influence of age and orthographic depth and their interaction on the neurobiology of reading we meta-analyzed 34 fMRI studies by combining the CluB and the GingerALE methods. Our meta-analytic results challenged both models and allowed us to generate a refined neurocognitive framework called the “Anatomo-functional, Developmental, and Orthographic Depth (ADOD) model of DD”. The ADOD model describes the interacting effects of age and orthography on the neurobiology of DD and suggests brand new conceptions on the role of the left TP cortex in reading together with a subtler parcellation of the vOT areas according to a rostro-caudal gradient
Reading the dyslexic brain: Multiple dysfunctional routes revealed by a new meta-analysis of PET and fMRI activation studies
No full textDevelopmental dyslexia has been the focus of much functional anatomical research. The main trust of this work is that typical developmental dyslexics have a dysfunction of the phonological and orthography to phonology conversion systems, in which the left occipito-temporal cortex has a crucial role. It remains to be seen whether there is a systematic co-occurrence of dysfunctional patterns of different functional systems perhaps converging on the same brain regions associated with the reading deficit. Such evidence would be relevant for theories like, for example, the magnocellular/attentional or the motor/cerebellar ones, which postulate a more basic and anatomically distributed disorder in dyslexia. We addressed this issue with a meta-analysis of all the imaging literature published until September 2013 using a combination of hierarchical clustering and activation likelihood estimation methods. The clustering analysis on 2360 peaks identified 193 clusters, 92 of which proved spatially significant. Following binomial tests on the clusters, we found left hemispheric network specific for normal controls (i.e., of reduced involvement in dyslexics) including the left inferior frontal, premotor, supramarginal cortices and the left infero-temporal and fusiform regions: these were preferentially associated with reading and the visual-to-phonology processes. There was also a more dorsal left fronto-parietal network: these clusters included peaks from tasks involving phonological manipulation, but also motoric or visuo-spatial perception/attention. No cluster was identified in area V5 for no task, nor cerebellar clusters showed a reduced association with dyslexics. We conclude that the examined literature demonstrates a specific lack of activation of the left occipito-temporal cortex in dyslexia particularly for reading and reading-like behaviors and for visuo-phonological tasks. Additional deficits of motor and attentional systems relevant for reading may be associated with altered functionality of dorsal left fronto-parietal corte
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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