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tDCS modulates the activity of the neuronal networks to induce the desired behavioural changes. Two factors determine its effectiveness- (1) whether the network being stimulated is relevant to the task, and (2) if there is a scope for improvement in behavioral performance. To explore this, both dorsal (sub-lexical) and ventral (lexical) reading networks were stimulated (20 min, 2 mA) in 25 healthy young volunteers. Participants performed two reading tasks with different levels of lexical involvement: word fragment completion tasks (WCT) and word association tasks (WAT), while event-related potentials (ERPs) were recorded simultaneously. The study used a within-subject design over three sessions, comparing various electrode montages targeting the dorsal pathway's left inferior parietal lobule or the ventral reading pathway's left middle temporal lobule, as well as sham stimulation. The impact of tDCS sessions (dorsal, ventral, & sham) and task type (WCT & WAT) on priming effects (primed vs. unprimed) of behavioral performance (accuracy and reaction times), and ERP parameters (N400 amplitudes and latencies) were statistically analyzed.It was found that tDCS modulated the performance of WAT only (a task with a lower priming effect). The failure to modulate WCT (larger priming effect) indicated that tDCS was effective for conditions with room for improvement compared to a task where performance has reached the ceiling. Ventral stimulation enhanced accuracy in the WAT condition and shortened the N400 latency of the priming effect. In contrast, dorsal stimulation delayed the priming effect reaction time in the WAT condition and enhanced the N400 amplitude. To conclude, enhancement in performance due to tDCS occurs when the network (ventral) being stimulated aligns with the cognitive demands of the task and there is a scope for improvement. [ABSTRACT FROM AUTHOR]

Language outcomes after speech and language therapy in post-stroke aphasia are challenging to predict. This study examines behavioral language measures and resting state fMRI (rsfMRI) as predictors of treatment outcome. Fifty-seven patients with chronic aphasia were recruited and treated for one of three aphasia impairments: anomia, agrammatism, or dysgraphia. Treatment effect was measured by performance on a treatment-specific language measure, assessed before and after three months of language therapy. Each patient also underwent an additional 27 language assessments and a rsfMRI scan at baseline. Patient scans were decomposed into 20 components by group independent component analysis, and the fractional amplitude of low-frequency fluctuations (fALFF) was calculated for each component time series. Post-treatment performance was modelled with elastic net regression, using pre-treatment performance and either behavioral language measures or fALFF imaging predictors. Analysis showed strong performance for behavioral measures in anomia (R2 = 0.948, n = 28) and for fALFF predictors in agrammatism (R2 = 0.876, n = 11) and dysgraphia (R2 = 0.822, n = 18). Models of language outcomes after treatment trained using rsfMRI features may outperform models trained using behavioral language measures in some patient populations. This suggests that rsfMRI may have prognostic value for aphasia therapy outcomes. [ABSTRACT FROM AUTHOR]

Previous research has shown that the components of Chinese characters (e.g., semantic components, phonetic components, and radicals) serve as processing units in reading. One outstanding question concerns the existence of amodal orthographic representations that unify multiple, form-specific character components, similar to the abstract letter identities (ALIs) that unify case-specific letter forms (A/a) in Roman script. Although Chinese does not have case, a subset of semantic radicals have multiple forms (e.g., 氵–水 are both "water" radicals), allowing for a test of the existence of Abstract Radical Identities (ARIs) that unify the multiple forms. In Experiment 1, a visual same–different judgement task was used to detect the presence of ARI representations. Evidence for ARIs was provided by the finding that radical pairs with different forms but the same radical identity were judged to be visually different more slowly than matched pairs of different forms with different radical identities. In Experiment 2, we evaluated ARI effects in real character reading. A lexical decision priming task compared prime–target character pairs containing radicals with the same identity but different forms (e.g., 泄–泉) with matched prime–target character pairs with unrelated radicals (e.g., 無–泉). Inhibitory priming was observed only in the same-identity radical condition compared with the unrelated condition. These combined results provide, for the first time, evidence of format-free representations of orthographic units in Chinese characters—abstract radical identities (ARIs). [ABSTRACT FROM AUTHOR]

Given the increased interest in the functional human connectome, a number of computer simulation studies have sought to develop a better quantitative understanding of the effects of focal lesions on the brain's functional network organization. However, there has been little work evaluating the predictions of this simulation work vis a vis real lesioned connectomes. One of the few relevant studies reported findings from real chronic focal lesions that only partially confirmed simulation predictions. We hypothesize that these discrepancies arose because although the effects of focal lesions likely consist of two components: short-term node subtraction and long-term network re-organization, previous simulation studies have primarily modeled only the short-term consequences of the subtraction of lesioned nodes and their connections. To evaluate this hypothesis, we compared network properties (modularity, participation coefficient, within-module degree) between real functional connectomes obtained from chronic stroke participants and "pseudo-lesioned" functional connectomes generated by subtracting the same sets of lesioned nodes/connections from healthy control connectomes. We found that, as we hypothesized, the network properties of real-lesioned connectomes in chronic stroke differed from those of the pseudo-lesioned connectomes which instantiated only the short-term consequences of node subtraction. Reflecting the long-term consequences of focal lesions, we found re-organization of the neurotopography of global and local hubs in the real but not the pseudo-lesioned connectomes. We conclude that the long-term network re-organization that occurs in response to focal lesions involves changes in functional connectivity within the remaining intact neural tissue that go well beyond the short-term consequences of node subtraction. [ABSTRACT FROM AUTHOR]

Fluent, adult readers of alphabetic languages encounter hundreds of millions of individual letters. What is the impact of such extensive experience on the perception and identification of letters? Recent evidence indicates that expert and naïve observers perceive letters differently. Here, we focus on the relationship between expertise and letter complexity (number of visual features) and distinctiveness (overlap in features with the other letters of the alphabet). Using a same-different letter judgement task, we examined the performance of individuals with high levels of expertise with Roman letters, but with different amounts of experience with the Arabic alphabet. The results reveal a trade-off between letter complexity and distinctiveness, such that while naïve individuals are sensitive only to letter complexity and not distinctiveness, the opposite is true for individuals with high expertise with an alphabet. These findings reveal a learning trajectory in which, with increasing experience, the influence of letter complexity is supplanted by distinctiveness, which requires an understanding of the relationship of each letter to the other possible letter shapes in the alphabet as a whole. [ABSTRACT FROM AUTHOR]

In three experiments, we examined whether similar principles apply to written and spoken production. Using a blocked cyclic written picture naming paradigm, we replicated the semantic interference effects previously reported in spoken production (Experiment 1). Using a written spelling-to-dictation blocked cyclic naming task, we also demonstrated that these interference effects disappear when the task does not require semantically-mediated lexical selection (Experiment 2). Results are parallel to those reported for the analogous spoken production task of reading aloud. Similar results were observed in written spelling to dictation regardless of whether stimuli consisted of words with high or low probability phoneme-to-grapheme correspondences (Experiment 3) revealing the important role of non-semantically-mediated spelling routes in written word production. Overall, our results support the view that similar mechanisms underlie written and spoken production. This includes an incremental learning mechanism underlying semantically-mediated lexical selection that produces long-lived interference effects when multiple semantically similar items are repeatedly named. [ABSTRACT FROM AUTHOR]

Past research has demonstrated interference effects when words are named in the context of multiple items that share a meaning. This interference has been explained within various incremental learning accounts of word production, which propose that each attempt at mapping semantic features to lexical items induces slight but persistent changes that result in cumulative interference. We examined whether similar interference-generating mechanisms operate during the mapping of lexical items to segments by examining the production of words in the context of others that share segments. Previous research has shown that initial-segment overlap amongst a set of target words produces facilitation, not interference. However, this initial-segment facilitation is likely due to strategic preparation, an external factor that may mask underlying interference. In the present study, we applied a novel manipulation in which the segmental overlap across target items was distributed unpredictably across word positions, in order to reduce strategic response preparation. This manipulation led to interference in both spoken (Exp. 1) and written (Exp. 2) production. We suggest that these findings are consistent with a competitive learning mechanism that applies across stages and modalities of word production. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

We describe the complex pattern of spared and impaired performance observed in a neurologically impaired subject on a number of letter processing tasks including: written letter naming, alphabetization, matching across typecase and font, oral and written spelling to dictation, and across-case letter priming. The observed dissociation in performance between the naming of written letters and the naming of letters in oral spelling as well as the dissociation between oral spelling and written spelling are shown to support a model of letter processing in which a distinction is drawn between visuo-spatial and abstract levels of letter representation. We also describe symmetrical deficits in the reading and writing of letters. These can be understood: in reading, as the result of an impairment to the processes which mediate the conversion of visuo-spatial letter representations to abstract representations, and in writing, as a deficit to the processes which negotiate the apparently reverse operation. This finding is interpreted within the context of the notions of neural and functional proximity and we raise the possibility that processes which perform distinct computations may, nonetheless, share certain computational resources. [ABSTRACT FROM AUTHOR]

Modulating higher cognitive functions like reading with transcranial direct current stimulation (tDCS) can be challenging as reading involves regions in the dorsal and ventral cortical areas that lie in close proximity. If the two pathways are stimulated simultaneously, the function of dorsal pathway (predominantly used for graphophonological conversion) might interfere with the function of the ventral pathway (used for semantics), and vice-versa. To achieve functional specificity in tDCS for investigating the two pathways of reading, it is important to stimulate each pathway per session such that the spread of current across the cortical areas due to the two montages has minimal overlap. The present study intends to achieve this by introducing a systematic approach for tDCS analysis. We employed the COMETS2 software to simulate 10 montage configurations (5 for each pathway) for three electrode sizes: 5 × 5, 3 × 3, and 5 × 7 cm2. This diversity in montage configuration is chosen since previous studies found the position and the size of anode and cathode to play an important role. The values of the magnitude of current density (MCD) obtained from the configuration were used to calculate: (i) average MCD in each cortical lobe, (ii) number of overlapping coordinates, and (iii) cortical areas with high MCD. The measures (i) and (iii) ascertained the current spread by each montage within a cortical lobe, and (ii) verified the overlap of the spread of current between a pair of montages. The analyses show that a montage using the electrode size of 5 × 5 cm2 with the anode at CP5 and cathode at CZ, and another with anode at TP7 and cathode at nape of the neck are optimal choices for dorsal and ventral pathways, respectively. To verify, we cross-validated the results with ROAST. This systematic approach was helpful in reducing the ambiguity of montage selection prior to conducting a tDCS study. [ABSTRACT FROM AUTHOR]

Multiple neurocognitive processes are involved in the highly complex task of producing written words. Yet, little is known about the neural pathways that support spelling in healthy adults. We assessed the associations between performance on a difficult spelling-to-dictation task and microstructural properties of language-related white matter pathways, in a sample of 73 native English-speaking neurotypical adults. Participants completed a diffusion magnetic resonance imaging scan and a cognitive assessment battery. Using constrained spherical deconvolution modeling and probabilistic tractography, we reconstructed dorsal and ventral white matter tracts of interest, bilaterally, in individual participants. Spelling associations were found in both dorsal and ventral stream pathways. In high-performing spellers, spelling scores significantly correlated with fractional anisotropy (FA) within the left inferior longitudinal fasciculus, a ventral stream pathway. In low-performing spellers, spelling scores significantly correlated with FA within the third branch of the right superior longitudinal fasciculus, a dorsal pathway. An automated analysis of spelling errors revealed that high- and low- performing spellers also differed in their error patterns, diverging primarily in terms of the orthographic distance between their errors and the correct spelling, compared to the phonological plausibility of their spelling responses. The results demonstrate the complexity of the neurocognitive architecture of spelling. The distinct white matter associations and error patterns detected in low- and high- performing spellers suggest that they rely on different cognitive processes, such that high-performing spellers rely more on lexical-orthographic representations, while low-performing spellers rely more on phoneme-to-grapheme conversion. [ABSTRACT FROM AUTHOR]