Development of spatial integration depends on top-down and interhemispheric connections that can be perturbed in migraine: a DCM analysis.

In humans, spatial integration develops slowly, continuing through childhood into adolescence. On the assumption that this protracted course depends on the formation of networks with slowly developing top-down connections, we compared effective connectivity in the visual cortex between 13 children (age 7-13) and 14 adults (age 21-42) using a passive perceptual task. The subjects were scanned while viewing bilateral gratings, which either obeyed Gestalt grouping rules [colinear gratings (CG)] or violated them [non-colinear gratings (NG)]. The regions of interest for dynamic causal modeling were determined from activations in functional MRI contrasts stimuli > background and CG > NG. They were symmetrically located in V1 and V3v areas of both hemispheres. We studied a common model, which contained reciprocal intrinsic and modulatory connections between these regions. An analysis of effective connectivity showed that top-down modulatory effects generated at an extrastriate level and interhemispheric modulatory effects between primary visual areas (all inhibitory) are significantly weaker in children than in adults, suggesting that the formation of feedback and interhemispheric effective connections continues into adolescence. These results are consistent with a model in which spatial integration at an extrastriate level results in top-down messages to the primary visual areas, where they are supplemented by lateral (interhemispheric) messages, making perceptual encoding more efficient and less redundant. Abnormal formation of top-down inhibitory connections can lead to the reduction of habituation observed in migraine patients

Inhibition in early Alzheimer's disease: an fMRI-based study of effective connectivity.

Changes of functional connectivity in prodromal and early Alzheimer's disease can arise from compensatory and/or pathological processes. We hypothesized that i) there is impairment of effective inhibition associated with early Alzheimer's disease that may lead to ii) a paradoxical increase of functional connectivity. To this end we analyzed effective connectivity in 14 patients and 16 matched controls using dynamic causal modeling of functional MRI time series recorded during a visual inter-hemispheric integration task. By contrasting co-linear with non co-linear bilateral gratings, we estimated inhibitory top-down effects within the visual areas. The anatomical areas constituting the functional network of interest were identified with categorical functional MRI contrasts (Stimuli>Baseline and Co-linear gratings>Non co-linear gratings), which implicated V1 and V3v in both hemispheres. A model with reciprocal excitatory intrinsic connections linking these four regions and modulatory inhibitory effects exerted by V3v on V1 optimally explained the functional MRI time series in both subject groups. However, Alzheimer's disease was associated with significantly weakened intrinsic and modulatory connections. Top-down inhibitory effects, previously detected as relative deactivations of V1 in young adults, were observed neither in our aged controls nor in patients. We conclude that effective inhibition weakens with age and more so in early Alzheimer's disease

Text Data-Hiding for Digital and Printed Documents: Theoretical and Practical Considerations

In this paper, we propose a new theoretical framework for the data-hiding problem of digital and printed text documents. We explain how this problem can be seen as an instance of the well-known Gel'fand-Pinsker problem. The main idea for this interpretation is to consider a text character as a data structure consisting of multiple quantifiable features such as shape, position, orientation, size, color, etc. We also introduce color quantization, a new semi-fragile text data-hiding method that is fully automatable, has high information embedding rate, and can be applied to both digital and printed text documents. The main idea of this method is to quantize the color or luminance intensity of each character in such a manner that the human visual system is not able to distinguish between the original and quantized characters, but it can be easily performed by a specialized reader machine. We also describe halftone quantization, a related method that applies mainly to printed text documents. Since these methods may not be completely robust to printing and scanning, an outer coding layer is proposed to solve this issue. Finally, we describe a practical implementation of the color quantization method and present experimental results for comparison with other existing methods

A Theoretical Framework for Data-Hiding in Digital and Printed Text Documents

In this work, we consider the text data-hiding problem as a particular instance of the well-known Gel’fand-Pinsker problem [1]. The text, where some message m ∈ M is to be hidden, is represented by x and called cover text. Each component xi, i = 1,2,...,N, of x represents one character from this text. Here, we define a character as an element from a given language alphabet (e.g. the latin alphabet {A, B,..., Z}). To be more precise, we conceive each character xi as a data structure consisting of multiple component fields (features): name, shape, position, orientation, size, color, etc. Assuming the knowledge of the conditional probability distribution p(u|x), |M||J | codewords u are generated independently at random and located into |M | bins, each of them with |J | codewords. Once generated, the codebook is revealed to both the encoder and the decoder. Given m to be communicated, the encoder produces the watermark w by finding first a jointly strongly typical pair (x,u(m,j)), where u(m,j) is the j-th codeword inside the bin corresponding to m, and then, by using a deterministic mapping w = ϕ N (x,u). The influence o

A Theoretical Framework for Data-Hiding Data Hiding in Digital and Printed Text Documents

• Is the problem of text data-hiding data hiding too difficult to solve? • Answer depends on the application requirements: • If robust data-hiding is required (e.g. copyright protection): probably YES, the attacker can always use Optical Character Recognition. • If either semi-fragile or fragile data-hiding is required (e.g. identification, authentication and tamper proofing): NO • Goals: • New theoretical framework for the text data-hiding problem. • New semi-fragile text data-hiding method, color quantization, that is fully automatable, has high information embedding rate, is resistant to printing and scanning, and can be applied to both digital and printed text documents. Gel’fand Gel fand-Pinske

Demyelination in mild cognitive impairment suggests progression path to Alzheimer's disease.

The preclinical Alzheimer's disease (AD) - amnestic mild cognitive impairment (MCI) - is manifested by phenotypes classified into exclusively memory (single-domain) MCI (sMCI) and multiple-domain MCI (mMCI). We suggest that typical MCI-to-AD progression occurs through the sMCI-to-mMCI sequence as a result of the extension of initial pathological processes. To support this hypothesis, we assess myelin content with a Magnetization Transfer Ratio (MTR) in 21 sMCI and 21 mMCI patients and in 42 age-, sex-, and education-matched controls. A conjunction analysis revealed MTR reduction shared by sMCI and mMCI groups in the medial temporal lobe and posterior structures including white matter (WM: splenium, posterior corona radiata) and gray matter (GM: hippocampus; parahippocampal and lingual gyri). A disjunction analysis showed the spread of demyelination to prefrontal WM and insula GM in executive mMCI. Our findings suggest that demyelination starts in the structures affected by neurofibrillary pathology; its presence correlates with the clinical picture and indicates the method of MCI-to-AD progression. In vivo staging of preclinical AD can be developed in terms of WM/GM demyelination