Diffusion-Weighted Magnetic Resonance Imaging as a Cancer Biomarker: Consensus and Recommendations

http://www.mpi.nl/world/materials/publications/Levelt/Indefrey_Levelt2004.pdf

The spatial and temporal signatures of word production components.

This paper elaborates on the components of a working definition of developmental dyslexia. It follows the general format of a paper by Lyon published in Annals of Dyslexia in 1995, which elaborated on a working definition proposed in 1994 (Lyon, 1995). The current definition agreed on by the work group updates and expands on the working definition from 1994.

A Definition of Dyslexia.

https://www.cogsci.ucsd.edu/~coulson/CNL/vwfa-review.pdf

The visual word form area: expertise for reading in the fusiform gyrus

http://ecuanst.weebly.com/uploads/6/0/6/0/60601319/cognitive_rehabilitation-_meta-analysis_and_review.pdf

Evidence-based cognitive rehabilitation: updated review of the literature from 2003 through 2008.

The inferior occipitotemporal brain areas, especially in the left hemisphere, have been shown to be involved in the processing of written words and letter strings. This processing probably occurs within 200 ms after presentation of the letter string. It has also been suggested that this activation may differ between fluent and dyslexic readers. Using whole-head magnetoencephalography, we studied the spatiotemporal dynamics of brain processes evoked by visually presented letter strings in 12 healthy adult subjects. Our achromatic stimuli consisted of rectangular patches in which single letters, two-letter syllables, four-letter words, or symbol strings of equal length were embedded and to which variable noise was added. This manipulation dissociated three different response patterns. The first of these patterns took place approximately 100 ms after stimulus onset, originated in areas surrounding the V1 cortex and was distributed along the ventral visual stream, extending laterally as far as V4v. This response was systematically modulated by noise but was insensitive to the stimulus content, suggesting involvement in early visual analysis. The second pattern took place approximately 150 ms after stimulus onset and was concentrated in the inferior occipitotemporal region with left-hemisphere dominance. This activation showed a preference for letter strings, and its strength and timing correlated with the speed at which the subjects were able to read words aloud. The third pattern also occurred in the time window approximately 150 ms after stimulus onset, but originated mainly in the right occipital area. Like the second pattern, it was modulated by string length, but showed no preference for letters compared with symbols. The present data strongly support the special role of the left inferior occipitotemporal cortex in visual word processing within 200 ms after stimulus onset.

Dynamics of letter string perception in the human occipitotemporal cortex

Recent studies have yielded contradictory evidence on whether visual speech perception (watching articulatory gestures) can activate the human primary auditory cortex. To circumvent confounds due to inter-individual anatomical variation, we defined our subjects' Heschl's gyri and assessed blood oxygenation-dependent signal changes at 3 T within this confined region during visual speech perception and observation of moving circles. Visual speech perception activated Heschl's gyri in nine subjects, with activation in seven of them extending to the area of primary auditory cortex. Activation was significantly stronger during visual speech perception than during observation of the moving circles. Further, a significant hemisphere by stimulus interaction occurred, suggesting left Heschl's gyrus specialization for visual speech processing.

Primary auditory cortex activation by visual speech: an fMRI study at 3 T.

Neuroimaging studies have revealed that the functional organization of reading differs between developmentally dyslexic and nonimpaired individuals However, it is not clear how early in the reading process the differences between fluent and dyslexic readers start to emerge We studied cortical activity of ten dyslexic adults using magnetoencephalography (MEG), as they silently read words or viewed symbol-strings which were clearly visible or degraded with Gaussian noise This method has previously been used to dissociate between analysis of local features and pre-lexical word processing in fluent adult readers Signals peaking around 100 ms after stimulus onset and originating in the postero-medial extrastriate cortex were associated with increasing local luminance contrast in the noise patches These early visual responses were similar in dyslexic and non-impaired readers In contrast, the letter-string-specific responses peaking around 150 ms predominantly in the left inferior occipito-temporal cortex in fluent readers were undetectable in dyslexic readers Thus, while the early visual processing seems intact in dyslexic adults, the pattern of cortical activation starts to differ from that of fluent readers at the point where letter-stringspecific signals first emerge during reading

Dissociation of Normal Feature Analysis and Deficient Processing of Letter-strings in Dyslexic Adults

Neurones in the human inferior occipitotemporal cortex respond to specific categories of images, such as numbers, letters and faces, within 150-200 ms. Here we identify the locus in time when stimulus-specific analysis emerges by comparing the dynamics of face and letter-string perception in the same 10 individuals. An ideal paradigm was provided by our previous study on letter-strings, in which noise-masking of stimuli revealed putative visual feature processing at 100 ms around the occipital midline followed by letter-string-specific activation at 150 ms in the left inferior occipitotemporal cortex. In the present study, noise-masking of cartoon-like faces revealed that the response at 100 ms increased linearly with the visual complexity of the images, a result that was similar for faces and letter-strings. By 150 ms, faces and letter-strings had entered their own stimulus-specific processing routes in the inferior occipitotemporal cortex, with identical timing and large spatial overlap. However, letter-string analysis lateralized to the left hemisphere, whereas face processing occurred more bilaterally or with right-hemisphere preponderance. The inferior occipitotemporal activations at approximately 150 ms, which take place after the visual feature analysis at approximately 100 ms, are likely to represent a general object-level analysis stage that acts as a rapid gateway to higher cognitive processing.

Dynamics of visual feature analysis and object-level processing in face versus letter-string perception.

We describe a study where a specific treatment method for word-finding difficulty (so-called contextual priming technique, which combines massive repetition priming with semantic priming) was applied with three chronic left hemisphere-damaged aphasics. Both before and after treatment, which focused on naming of a series of pictures, naming-related brain activity was measured by magnetoencephalography (MEG). Due to its excellent temporal resolution and good spatial resolution, we were able to track treatment-induced changes in cortical activity. All three subjects showed improved naming of the trained items. In all subjects, a single source area, located in the left inferior parietal lobe, close to the lesioned area, displayed statistically significant training-induced changes. This effect was of long latency as it started 300-600 msec after picture presentation. The change in activation was specific to training, as it could not be accounted for by variation of cortical dynamics associated with increased proportion of correct answers. Our interpretation is that the training effect reflects more effective phonological encoding and storage of the trained items through the engagement of a left hemispheric word-learning system. This is in line with recent functional imaging studies, which have linked left inferior parietal lobe activity to the phonological storage component of the verbal working memory, as well as with theoretical arguments stating that the primary role of the phonological loop is to acquire new words. Finally, the MEG results showed no evidence of increased right hemisphere participation following training, supporting the view that restoration of language-related networks in the damaged left hemisphere is crucial for anomia recovery.

/pdf/adult-brain-plasticity-elicited-by-anomia-treatment-daq4a5dgdi.pdf

Antti Tarkiainen

Papers

Dynamics of letter string perception in the human occipitotemporal cortex

Primary auditory cortex activation by visual speech: an fMRI study at 3 T.

Dissociation of Normal Feature Analysis and Deficient Processing of Letter-strings in Dyslexic Adults

Dynamics of visual feature analysis and object-level processing in face versus letter-string perception.

Adult Brain Plasticity Elicited by Anomia Treatment