Effects of literacy in early visual and occipitotemporal areas of Chinese and French readers

Writing letters in two graphic systems: Behavioral and neural correlates in Latin-Arabic biscripters

Biscriptuality is the ability to read and write using two scripts. Despite the increasing number of biscripters, this phenomenon remains poorly understood. Here, we focused on investigating graphomotor processing in French-Arabic biscripters. We chose the French and Arabic alphabets because they have comparable visuospatial complexity and linguistic features, but differ dramatically in their graphomotor characteristics. In a first experiment we describe the graphomotor features of the two alphabets and showed that while Arabic and Latin letters are produced with the same velocity and fluency, Arabic letters require more pen lifts, contain more right-to-left strokes and clockwise curves, and take longer to write than Latin letters. These results suggest that Arabic and Latin letters are produced via different motor patterns. In a second experiment we used functional magnetic resonance imaging to ask whether writing the two scripts relies upon partially distinct or fully overlapping neural networks, and whether the elements of the previously described handwriting network are recruited to the same extent by the two scripts. We found that both scripts engaged the so-called "writing network", but that within the network, Arabic letters recruited the left superior parietal lobule (SPL) and the left primary motor cortex (M1) more strongly than Latin letters. Both regions have previously been identified as holding scale-invariant representations of letter trajectories. Arabic and Latin letters also activated distinct regions that do not belong to the writing network. Complementary analyses indicate that the differences observed between scripts at the neural level could be driven by the specific graphomotor features of each script. Overall, our results indicate that particular features of the practiced scripts can lead to different motor organization at both the behavioral and brain levels in biscripters.

Lexical and sublexical cortical tuning for print revealed by Steady-State Visual Evoked Potentials (SSVEPs) in early readers

There are multiple levels of processing relevant to reading that vary in their visual, sublexical, and lexical orthographic processing demands. Segregating distinct cortical sources for each of these levels has been challenging in EEG studies of early readers. To address this challenge, we applied recent advances in analyzing high-density EEG using Steady-State Visual Evoked Potentials (SSVEPs) via data-driven Reliable Components Analysis (RCA) in a group of early readers spanning from kindergarten to second grade. Three controlled stimulus contrasts-familiar words versus unfamiliar pseudofonts, familiar words versus pseudowords, and pseudowords versus nonwords-were used to isolate coarse print tuning, lexical processing, and sublexical orthography-related processing, respectively. First, three overlapping yet distinct neural sources-left vOT, dorsal parietal, and primary visual cortex were revealed underlying coarse print tuning. Second, we segregated distinct cortical sources for the other two levels of processing: lexical fine tuning over occipito-temporal/parietal regions; sublexical orthographic fine tuning over left occipital regions. Finally, exploratory group analyses based on children's reading fluency suggested that coarse print tuning emerges early even in children with limited reading knowledge, while sublexical and higher-level lexical processing emerge only in children with sufficient reading knowledge. RESEARCH HIGHLIGHTS: Cognitive processes underlying coarse print tuning, sublexical, and lexical fine tuning were examined in beginning readers. Three overlapping yet distinct neural sources-left ventral occipito-temporal (vOT), left temporo-parietal, and primary visual cortex-were revealed underlying coarse print tuning. Responses to sublexical orthographic fine tuning were found over left occipital regions, while responses to higher-level linguistic fine tuning were found over occipito-temporal/parietal regions. Exploratory group analyses suggested that coarse print tuning emerges in children with limited reading knowledge, while sublexical and higher-level linguistic fine tuning effects emerge in children with sufficient reading knowledge.

Does the visual word form area split in bilingual readers? A millimeter-scale 7-T fMRI study

In expert readers, a brain region known as the visual word form area (VWFA) is highly sensitive to written words, exhibiting a posterior-to-anterior gradient of increasing sensitivity to orthographic stimuli whose statistics match those of real words. Using high-resolution 7-tesla functional magnetic resonance imaging (fMRI), we ask whether, in bilingual readers, distinct cortical patches specialize for different languages. In 21 English-French bilinguals, unsmoothed 1.2-millimeters fMRI revealed that the VWFA is actually composed of several small cortical patches highly selective for reading, with a posterior-to-anterior word-similarity gradient, but with near-complete overlap between the two languages. In 10 English-Chinese bilinguals, however, while most word-specific patches exhibited similar reading specificity and word-similarity gradients for reading in Chinese and English, additional patches responded specifically to Chinese writing and, unexpectedly, to faces. Our results show that the acquisition of multiple writing systems can indeed tune the visual cortex differently in bilinguals, sometimes leading to the emergence of cortical patches specialized for a single language.

Graph theoretical analysis reveals the functional role of the left ventral occipito-temporal cortex in speech processing

The left ventral occipito-temporal cortex (left-vOT) plays a key role in reading. Interestingly, the area also responds to speech input, suggesting that it may have other functions beyond written word recognition. Here, we adopt graph theoretical analysis to investigate the left-vOT's functional role in the whole-brain network while participants process spoken sentences in different contexts. Overall, different connectivity measures indicate that the left-vOT acts as an interface enabling the communication between distributed brain regions and sub-networks. During simple speech perception, the left-vOT is systematically part of the visual network and contributes to the communication between neighboring areas, remote areas, and sub-networks, by acting as a local bridge, a global bridge, and a connector, respectively. However, when speech comprehension is explicitly required, the specific functional role of the area and the sub-network to which the left-vOT belongs change and vary with the quality of speech signal and task difficulty. These connectivity patterns provide insightful information on the contribution of the left-vOT in various contexts of language processing beyond its role in reading. They advance our general understanding of the neural mechanisms underlying the flexibility of the language network that adjusts itself according to the processing context.

Evolution of reading and face circuits during the first three years of reading acquisition

Although words and faces activate neighboring regions in the fusiform gyrus, we lack an understanding of how such category selectivity emerges during development. To investigate the organization of reading and face circuits at the earliest stage of reading acquisition, we measured the fMRI responses to words, faces, houses, and checkerboards in three groups of 60 French children: 6-year-old pre-readers, 6-year-old beginning readers and 9-year-old advanced readers. The results showed that specific responses to written words were absent prior to reading, but emerged in beginning readers, irrespective of age. Likewise, specific responses to faces were barely visible in pre-readers and continued to evolve in the 9-year-olds, yet primarily driven by age rather than by schooling. Crucially, the sectors of ventral visual cortex that become specialized for words and faces harbored their own functional connectivity prior to reading acquisition: the VWFA with left-hemispheric spoken language areas, and the FFA with the contralateral region and the amygdalae. The results support the view that reading acquisition occurs through the recycling of a pre-existing but plastic circuit which, in pre-readers, already connects the VWFA site to other distant language areas. We argue that reading acquisition does not compete with the face system directly, through a pruning of preexisting face responses, but indirectly, by hindering the slow growth of face responses in the left hemisphere, thus increasing a pre-existing right hemispheric bias.

The role of reading experience in atypical cortical tracking of speech and speech-in-noise in dyslexia

Dyslexia is a frequent developmental disorder in which reading acquisition is delayed and that is usually associated with difficulties understanding speech in noise. At the neuronal level, children with dyslexia were reported to display abnormal cortical tracking of speech (CTS) at phrasal rate. Here, we aimed to determine if abnormal tracking relates to reduced reading experience, and if it is modulated by the severity of dyslexia or the presence of acoustic noise. We included 26 school-age children with dyslexia, 26 age-matched controls and 26 reading-level matched controls. All were native French speakers. Children's brain activity was recorded with magnetoencephalography while they listened to continuous speech in noiseless and multiple noise conditions. CTS values were compared between groups, conditions and hemispheres, and also within groups, between children with mild and severe dyslexia. Syllabic CTS was significantly reduced in the right superior temporal gyrus in children with dyslexia compared with controls matched for age but not for reading level. Severe dyslexia was characterized by lower rapid automatized naming (RAN) abilities compared with mild dyslexia, and phrasal CTS lateralized to the right hemisphere in children with mild dyslexia and all control groups but not in children with severe dyslexia. Finally, an alteration in phrasal CTS was uncovered in children with dyslexia compared with age-matched controls in babble noise conditions but not in other less challenging listening conditions (non-speech noise or noiseless conditions); no such effect was seen in comparison with reading-level matched controls. Overall, our results confirmed the finding of altered neuronal basis of speech perception in noiseless and babble noise conditions in dyslexia compared with age-matched peers. However, the absence of alteration in comparison with reading-level matched controls demonstrates that such alterations are associated with reduced reading level, suggesting they are merely driven by reduced reading experience rather than a cause of dyslexia. Finally, our result of altered hemispheric lateralization of phrasal CTS in relation with altered RAN abilities in severe dyslexia is in line with a temporal sampling deficit of speech at phrasal rate in dyslexia.

Repetition Probability Effects for Chinese Characters and German Words in the Visual Word Form Area

The magnitude of repetition suppression (RS), measured by fMRI, is modulated by the probability of repetitions (P(rep)) for various sensory stimulus categories. It has been suggested that for visually presented simple letters this P(rep) effect depends on the prior practices of the participants with the stimuli. Here we tested further if previous experiences affect the neural mechanisms of RS, leading to the modulatory effects of stimulus P(rep), for more complex lexical stimuli as well. We measured the BOLD signal in the Visual Word Form Area (VWFA) of native Chinese and German participants and estimated the P(rep) effects for Chinese characters and German words. The results showed a significant P(rep) effect for stimuli of the mother tongue in both participant groups. Interestingly, Chinese participants, learning German as a second language, also showed a significant P(rep) modulation of RS for German words while the German participants who had no prior experiences with the Chinese characters showed no such effects. Our findings suggest that P(rep) effects on RS are manifest for visual word processing as well, but only for words of a language with which participants are highly familiar. These results support further the idea that predictive processes, estimated by P(rep) modulations of RS, require prior experiences.

The effects of stimulus inversion on the neural representations of Chinese character and face recognition

This study investigates whether stimulus inversion influences neural responses of Chinese character recognition similarly to its effect on face recognition in category-selective and object-related brain areas using functional magnetic resonance imaging. Participants performed a one-back matching task for simple (one radical) and compound (two radicals) Chinese characters and faces with upright and inverted orientations. Inverted stimuli produced slower response times with stronger activity within the fusiform gyrus (FG) than upright stimuli for faces and Chinese characters. While common inversion-related activation was identified in the left FG among stimulus types, we observed a significant inter-regional correlation between the left FG and the intraparietal sulcus for face inversion. Importantly, analyses of region-of-interest (ROI) multivariate pattern classification showed that classifiers trained on face inversion can decode the representations of character inversion in the character-selective ROI. However, this was not true for face inversion in face-selective ROIs when the classifiers were trained on characters. Similar activity patterns for character and face inversion were observed in the object-related ROIs. We also showed higher decoding accuracy for upright stimuli in the face-selective ROI than in the character-selective ROI but this was not true for inverted ones or when patterns were examined in the object-related ROIs. Together, our results support shared and distinct configural representations for character and face recognition in category-selective and object-related brain areas.

Acquired dyslexias following temporal lesions

The acquisition of reading by children is supported by deep changes in the brain systems devoted to vision and language. The left temporal lobe contributes critically to both systems, and lesions affecting it may therefore cause both peripheral vision-related and central language-related reading impairments. The diversity of peripheral dyslexias reflects the anatomical and functional division of the visual cortex into early visual regions, whose lesions have a limited impact on reading; ventral regions, whose lesions are mostly associated to Pure Alexia; and dorsal regions, whose lesions may yield spatial, neglect-related, and attentional dyslexias. Similarly, central alexias reflect the broad distinction, within language processes, between phonological and lexico-semantic components. Phonological and surface dyslexias roughly result from impairment of the former and the latter processes, respectively, while deep dyslexia may be seen as the association of both. In this chapter, we review such types of acquired dyslexias, their clinical features, pathophysiology, and anatomical correlates.

Nurturing the reading brain: home literacy practices are associated with children's neural response to printed words through vocabulary skills

Previous studies indicate that children are exposed to different literacy experiences at home. Although these disparities have been shown to affect children's literacy skills, it remains unclear whether and how home literacy practices influence brain activity underlying word-level reading. In the present study, we asked parents of French children from various socioeconomic backgrounds (n = 66; 8.46 ± 0.36 years, range 7.52-9.22; 20 girls) to report the frequency of home literacy practices. Neural adaptation to the repetition of printed words was then measured using functional magnetic resonance imaging (fMRI) in a subset of these children (n = 44; 8.49 ± 0.33 years, range 8.02-9.14; 13 girls), thereby assessing how sensitive was the brain to the repeated presentation of these words. We found that more frequent home literacy practices were associated with enhanced word adaptation in the left posterior inferior frontal sulcus (r = 0.32). We also found that the frequency of home literacy practices was associated with children's vocabulary skill (r = 0.25), which itself influenced the relation between home literacy practices and neural adaptation to words. Finally, none of these effects were observed in a digit adaptation task, highlighting their specificity to word recognition. These findings are consistent with a model positing that home literacy experiences may improve children's vocabulary skill, which in turn may influence the neural mechanisms supporting word-level reading.

Emergence of a compositional neural code for written words: Recycling of a convolutional neural network for reading

The visual word form area (VWFA) is a region of human inferotemporal cortex that emerges at a fixed location in the occipitotemporal cortex during reading acquisition and systematically responds to written words in literate individuals. According to the neuronal recycling hypothesis, this region arises through the repurposing, for letter recognition, of a subpart of the ventral visual pathway initially involved in face and object recognition. Furthermore, according to the biased connectivity hypothesis, its reproducible localization is due to preexisting connections from this subregion to areas involved in spoken-language processing. Here, we evaluate those hypotheses in an explicit computational model. We trained a deep convolutional neural network of the ventral visual pathway, first to categorize pictures and then to recognize written words invariantly for case, font, and size. We show that the model can account for many properties of the VWFA, particularly when a subset of units possesses a biased connectivity to word output units. The network develops a sparse, invariant representation of written words, based on a restricted set of reading-selective units. Their activation mimics several properties of the VWFA, and their lesioning causes a reading-specific deficit. The model predicts that, in literate brains, written words are encoded by a compositional neural code with neurons tuned either to individual letters and their ordinal position relative to word start or word ending or to pairs of letters (bigrams).

Distinct neural sources underlying visual word form processing as revealed by steady state visual evoked potentials (SSVEP)

EEG has been central to investigations of the time course of various neural functions underpinning visual word recognition. Recently the steady-state visual evoked potential (SSVEP) paradigm has been increasingly adopted for word recognition studies due to its high signal-to-noise ratio. Such studies, however, have been typically framed around a single source in the left ventral occipitotemporal cortex (vOT). Here, we combine SSVEP recorded from 16 adult native English speakers with a data-driven spatial filtering approach—Reliable Components Analysis (RCA)—to elucidate distinct functional sources with overlapping yet separable time courses and topographies that emerge when contrasting words with pseudofont visual controls. The first component topography was maximal over left vOT regions with a shorter latency (approximately 180 ms). A second component was maximal over more dorsal parietal regions with a longer latency (approximately 260 ms). Both components consistently emerged across a range of parameter manipulations including changes in the spatial overlap between successive stimuli, and changes in both base and deviation frequency. We then contrasted word-in-nonword and word-in-pseudoword to test the hierarchical processing mechanisms underlying visual word recognition. Results suggest that these hierarchical contrasts fail to evoke a unitary component that might be reasonably associated with lexical access.

Age of Acquisition of Mandarin Modulates Cortical Thickness in High-Proficient Cantonese-Mandarin Bidialectals

Previous studies showed that the onset age of second language acquisition (AoA-L2) can modulate brain structure of bilinguals. However, the underlying mechanism of anatomical plasticity induced by AoA-L2 is still a question in debate. In order to explore the issue, we recruited two groups of native Cantonese-Mandarin speakers, the early group began to speak in Mandarin at about 3.5 and the late group at about 6.5 years old. In addition, the early group had earlier experience in reading Chinese characters than the late group did. Through estimating the cortical thickness (CT), we found that (1) compared with the late group, the early group had thicker CT in the lateral occipital region, left middle temporal gyrus, and left parahippocampal region, which are all involved in visuospatial processing, probably reflecting the effect induced by the earlier or later experiences in processing the characters of Chinese for the two groups; and (2) compared with the late group, the early group had thicker CT in left superior parietal region, which is believed to be involved in language switching, maybe for the early group had the earlier experience in switching back and forth between Cantonese and Mandarin and therefore recruited the executive control network earlier. Our findings revealed the effects of the AoA-L2 in oral language acquisition as well as in written language acquisition as the main determinants of bilingual language structural representation in human brain.

Spatiotemporal dynamics of orthographic and lexical processing in the ventral visual pathway

Reading is a rapid, distributed process that engages multiple components of the ventral visual stream. To understand the neural constituents and their interactions that allow us to identify written words, we performed direct intra-cranial recordings in a large cohort of humans. This allowed us to isolate the spatiotemporal dynamics of visual word recognition across the entire left ventral occipitotemporal cortex. We found that mid-fusiform cortex is the first brain region sensitive to lexicality, preceding the traditional visual word form area. The magnitude and duration of its activation are driven by the statistics of natural language. Information regarding lexicality and word frequency propagates posteriorly from this region to visual word form regions and to earlier visual cortex, which, while active earlier, show sensitivity to words later. Further, direct electrical stimulation of this region results in reading arrest, further illustrating its crucial role in reading. This unique sensitivity of mid-fusiform cortex to sub-lexical and lexical characteristics points to its central role as the orthographic lexicon-the long-term memory representations of visual word forms.

Functional reorganization of the reading network in the course of foreign language acquisition

During foreign language acquisition neural representations of native language and foreign language assimilate. In the reading network, this assimilation leads to a shift from effortful processing to automated reading. Longitudinal studies can track this transition and reveal dynamics that might not become apparent in behavior. Here, we report results from a longitudinal functional magnetic resonance imaging (fMRI) study, which tracked functional changes in the reading network of beginning learners of Greek over one year. We deliberately chose Greek as foreign language that would have similar orthographic transparency but a different alphabet than the native language (Polish). fMRI scans with lexical and semantic decision tasks were performed at five different time points (every ~3 months). Classical language areas (the left inferior frontal gyrus, the left precentral gyrus, and the bilateral supplementary motor cortex), and cognitive control areas (left inferior parietal lobe and bilateral anterior cingulate cortex) showed stronger activation after the first months of instruction as compared to the activation before instruction. This pattern occured in both tasks. Task-related activity in the reading network remained constant throughout the remaining 6 months of learning and was also present in a follow-up scan 3 months after the end of the course. A similar pattern was demonstrated by the analysis of convergence between foreign and native languages occurring within the first months of learning. Additionally, in the lexical task, the extent of spatial overlap, between foreign and native language in Broca's area increased constantly from the beginning till the end of training. Our findings support the notion that reorganization of language networks is achieved after a relatively short time of foreign language instruction. We also demonstrate that cognitive control areas are recruited in foreign language reading at low proficiency levels. No apparent changes in the foreign or native reading network occur after the initial 3 months of learning. This suggests that task demand might be more important than proficiency in regulating the resources needed for efficient foreign language reading.

A universal reading network and its modulation by writing system and reading ability in French and Chinese children

Are the brain mechanisms of reading acquisition similar across writing systems? And do similar brain anomalies underlie reading difficulties in alphabetic and ideographic reading systems? In a cross-cultural paradigm, we measured the fMRI responses to words, faces, and houses in 96 Chinese and French 10-year-old children, half of whom were struggling with reading. We observed a reading circuit which was strikingly similar across languages and consisting of the left fusiform gyrus, superior temporal gyrus/sulcus, precentral and middle frontal gyri. Activations in some of these areas were modulated either by language or by reading ability, but without interaction between those factors. In various regions previously associated with dyslexia, reading difficulty affected activation similarly in Chinese and French readers, including the middle frontal gyrus, a region previously described as specifically altered in Chinese. Our analyses reveal a large degree of cross-cultural invariance in the neural correlates of reading acquisition and reading impairment.

Visual Processing Matters in Chinese Reading Acquisition and Early Mathematics

The main purpose of the present study was to investigate whether visual processing uniquely contributed to character reading and early mathematics in Chinese children. Eighty-two Chinese kindergarteners at K3 (mean age = 68 months, SD = 0.30) were followed up to grade one (mean age = 82 months, SD = 0.35) with an interval of 14 months. Nonverbal intelligence, inhibitory control, sustained attention, character reading, and mathematics were measured at kindergarten. Character reading and mathematics were assessed again at grade one. Results showed visual processing at kindergarten significantly predicted character reading at grade one after controlling for prior reading performance, inhibitory control, sustained attention, age, gender, and nonverbal IQ. Similarly, visual processing at kindergarten explained unique variance in early mathematics at grade one when prior mathematics performance and other covariates at kindergarten were controlled. These findings suggest that visual processing should serve as a domain-general precursor of children's performance in character reading and early mathematics and an important cognitive factor for later academic learning.

Advantage of detecting visual events in the right hemifield is affected by reading skill

Visual perception is often not homogenous across the visual field and can vary depending on situational demands. The reasons behind this inhomogeneity are not clear. Here we show that directing attention that is consistent with a western reading habit from left to right, results in a ~32% higher sensitivity to detect transient visual events in the right hemifield. This right visual field advantage was largely reduced in individuals with reading difficulties from developmental dyslexia. Similarly, visual detection became more symmetric in skilled readers, when attention was guided opposite to the reading pattern. Taken together, these findings highlight a higher sensitivity in the right visual field for detecting the onset of sudden visual events that is well accounted for by left hemisphere dominated reading habit.

Repetition enhancement to voice identities in the dog brain

In the human speech signal, cues of speech sounds and voice identities are conflated, but they are processed separately in the human brain. The processing of speech sounds and voice identities is typically performed by non-primary auditory regions in humans and non-human primates. Additionally, these processes exhibit functional asymmetry in humans, indicating the involvement of distinct mechanisms. Behavioural studies indicate analogue side biases in dogs, but neural evidence for this functional dissociation is missing. In two experiments, using an fMRI adaptation paradigm, we presented awake dogs with natural human speech that either varied in segmental (change in speech sound) or suprasegmental (change in voice identity) content. In auditory regions, we found a repetition enhancement effect for voice identity processing in a secondary auditory region - the caudal ectosylvian gyrus. The same region did not show repetition effects for speech sounds, nor did the primary auditory cortex exhibit sensitivity to changes either in the segmental or in the suprasegmental content. Furthermore, we did not find evidence for functional asymmetry neither in the processing of speech sounds or voice identities. Our results in dogs corroborate former human and non-human primate evidence on the role of secondary auditory regions in the processing of suprasegmental cues, suggesting similar neural sensitivity to the identity of the vocalizer across the mammalian order.

Reading Increases the Compositionality of Visual Word Representations

Reading causes widespread changes in the brain, but its effect on visual word representations is unknown. Learning to read may facilitate visual processing by forming specialized detectors for longer strings or by making word responses more predictable from single letters—that is, by increasing compositionality. We provided evidence for the latter hypothesis using experiments that compared nonoverlapping groups of readers of two Indian languages (Telugu and Malayalam). Readers showed increased single-letter discrimination and decreased letter interactions for bigrams during visual search. Importantly, these interactions predicted subjects’ overall reading fluency. In a separate brain-imaging experiment, we observed increased compositionality in readers, whereby responses to bigrams were more predictable from single letters. This effect was specific to the anterior lateral occipital region, where activations best matched behavior. Thus, learning to read facilitates visual processing by increasing the compositionality of visual word representations.

Dissociating the functions of superior and inferior parts of the left ventral occipito-temporal cortex during visual word and object processing

During word and object recognition, extensive activation has consistently been observed in the left ventral occipito-temporal cortex (vOT), focused around the occipito-temporal sulcus (OTs). Previous studies have shown that there is a hierarchy of responses from posterior to anterior vOT regions (along the y-axis) that corresponds with increasing levels of recognition - from perceptual to semantic processing, respectively. In contrast, the functional differences between superior and inferior vOT responses (i.e. along the z-axis) have not yet been elucidated. To investigate, we conducted an extensive review of the literature and found that peak activation for reading varies by more than 1 cm in the z-axis. In addition, we investigated functional differences between superior and inferior parts of left vOT by analysing functional MRI data from 58 neurologically normal skilled readers performing 8 different visual processing tasks. We found that group activation in superior vOT was significantly more sensitive than inferior vOT to the type of task, with more superior vOT activation when participants were matching visual stimuli for their semantic or perceptual content than producing speech to the same stimuli. This functional difference along the z-axis was compared to existing boundaries between cytoarchitectonic areas around the OTs. In addition, using dynamic causal modelling, we show that connectivity from superior vOT to anterior vOT increased with semantic content during matching tasks but not during speaking tasks whereas connectivity from inferior vOT to anterior vOT was sensitive to semantic content for matching and speaking tasks. The finding of a functional dissociation between superior and inferior parts of vOT has implications for predicting deficits and response to rehabilitation for patients with partial damage to vOT following stroke or neurosurgery.

Morphologic changes in the visual cortex of patients with anisometropic amblyopia: a surface-based morphometry study

Background

Amblyopia is generally considered a neurodevelopmental disorder that results from abnormal visual experiences in early childhood and may persist to adulthood. The neural basis of amblyopia has been a matter of interest for many decades, but the critical neural processing sites in amblyopia are not entirely understood. Although many functional neuroimaging studies have found abnormal neuronal responses both within and beyond V1, few studies have focused on the neurophysiologic abnormalities in the visual cortex from the viewpoint of potential structural reorganization. In this study, we used a well-validated and highly accurate surface-based method to examine cortical morphologic changes in the visual cortex using multiple parameters (including cortical thickness, surface area, volume and mean curvature).

Results

The cortical thicknesses of the bilateral V1, left V2, left ventral V3, left V4 and left V5/MT+ in patients were significantly thinner than that in controls. The mean curvature of the bilateral V1 was significantly increased in the patients compared with the controls. For the surface area and gray matter volume, no significant differences were found between patients and controls in all region of interests. The cortical thicknesses of the bilateral V1 were both negatively correlated with the amount of anisometropia. No significant correlations were found between any other surface parameters and clinical variables.

Conclusion

In addition to cortical thickness, the altered mean curvature of the cortex may indicate neuroanatomic impairments of the visual cortex in patients with anisometropic amblyopia. Moreover, the structural changes were bilateral in the primary visual cortex but were unilateral in the secondary and more senior visual cortex.

Orthographic Priming in Braille Reading as Evidence for Task-specific Reorganization in the Ventral Visual Cortex of the Congenitally Blind

The task-specific principle asserts that, following deafness or blindness, the deprived cortex is reorganized in a manner such that the task of a given area is preserved even though its input modality has been switched. Accordingly, tactile reading engages the ventral occipitotemporal cortex (vOT) in the blind in a similar way to regular reading in the sighted. Others, however, show that the vOT of the blind processes spoken sentence structure, which suggests that the task-specific principle might not apply to vOT. The strongest evidence for the vOT's engagement in sighted reading comes from orthographic repetition-suppression studies. Here, congenitally blind adults were tested in an fMRI repetition-suppression paradigm. Results reveal a double dissociation, with tactile orthographic priming in the vOT and auditory priming in general language areas. Reconciling our finding with other evidence, we propose that the vOT in the blind serves multiple functions, one of which, orthographic processing, overlaps with its function in the sighted.

Left-Hemisphere Delay of EEG Potentials Evoked by Standard Letter Stimuli During Rapid Serial Visual Presentation: Indicating Right-Hemisphere Advantage or Left-Hemisphere Load?

During rapid serial visual presentation (RSVP), two streams of letters simultaneously presented in the left and right visual fields (LVF and RVF) evoke visual potentials (VEPs) of EEG a few milliseconds earlier at the right (RH) than the left hemisphere (LH). This small LH VEP lag might be attributed to a RH advantage in initial processing of rapidly changing stimuli or to larger load of the LH by its specialized processing of letters from both visual fields simultaneously. In the present study, the two-stream condition was compared in two experiments to conditions with smaller instantaneous verbal load, namely with stimuli presented either solely or slightly earlier in the LVF or RVF. The RH advantage hypothesis predicts a LH VEP lag very similar to the standard two-stream condition when comparing between LH and RH VEPs contralateral to the single or earlier stream. The LH load hypothesis predicts shorter VEP latencies at the LH in the one-stream and earlier-stream than in the two-stream condition, resulting in an absent LH lag in those conditions. Results tended to be more in line with these latter predictions suggesting that in RSVP the LH might be more involved in partial processing of letters in search for target features. However, since the RH advantage hypothesis could not be reliably rejected these results might indicate a complex interplay between both hemispheres. This interplay would exploit the abilities of either hemisphere during the demanding processing of rapidly presented letters, both the LH advantage in letter processing and the RH advantage in visual perception at initial stages.

Integration and segregation of functional segmented anterior and posterior hippocampal networks in memory performance

PURPOSE

To determine the association between functional connectivity (FC) of functional-segmented anterior and posterior portions of the hippocampus and performance on verbal and visual memory tests in a young, healthy population.

METHODS

We recruited 100 healthy participants in the age of 19-29. Resting state fMRI data were acquired and voxel-wise correlation analysis was performed to functionally divide the hippocampus. We investigated the inter-hemispheric hippocampal-cortical functional connectivity after the participants took the assessment of episodic memory using verbal (California Verbal Learning Test II, CVLT-II) and visual subtests (Rey-Osterrieth Complex Figure, ROCF). The partial correlations were used to identify the association between the intra-hemispheric hippocampal-cortical mean resting correlation and memory performance.

RESULTS

The results showed that the anterior and posterior hippocampal networks involved differently in verbal and visual memory. Intra-hemispheric FC between left posterior hippocampus and posterior parahippocampal gyrus (PPHG) was positively correlated with CVLT-II Trail 2 Immediate Free Recall (r = 0.223, p = 0.029). Intra-hemispheric FC between left posterior hippocampus and posterior cingulate (PCC) was negatively correlated with ROCF Immediate Recall (r = -0.217 p = 0.034). Intra-hemispheric FC between left anterior hippocampus and temporal pole (TP) negatively correlated with ROCF Delayed Recall (r = -0.228, p = 0.025). Split half resampling procedure results showed some repeatability in our subjects.

CONCLUSION

The present results demonstrated that, the anterior hippocampus was specifically involved in the visual memory processing, whereas the posterior hippocampus contributed to both the verbal and visual memories, which may have implications for a functionally synergetic and dissociable role of the hippocampus in different kinds of memory.

Role-Specific Brain Activations in Leaders and Followers During Joint Action

Much of social interaction in human life requires that individuals perform different roles during joint actions, the most basic distinction being that between a leader and a follower. A number of neuroimaging studies have examined the brain networks for leading and following, but none have examined what effect prior expertise at these roles has on brain activations during joint motor tasks. Couple dancers (e.g., dancers of Tango, Salsa, and swing) are an ideal population in which examine such effects, since leaders and followers of partnered dances have similar overall levels of motor expertise at dancing, but can differ strikingly in their role-specific skill sets. To explore role-specific expertise effects on brain activations for the first time, we recruited nine skilled leaders and nine skilled followers of couple dances for a functional magnetic resonance imaging study. We employed a two-person scanning arrangement that allowed a more naturalistic interaction between two individuals. The dancers interacted physically with an experimenter standing next to the bore of the magnet so as to permit bimanual partnered movements. Together, they alternated between leading and following the joint movements. The results demonstrated that the brain activations during the acts of leading and following were enhanced by prior expertise at being a leader or follower, and that activity in task-specific brain areas tended to be positively correlated with the level of expertise at the corresponding role. These findings provide preliminary evidence that training at one role of a joint motor task can selectively enhance role-related brain activations.

Converging evidence for functional and structural segregation within the left ventral occipitotemporal cortex in reading

The ventral occipitotemporal cortex (vOTC) is crucial for recognizing visual patterns, and previous evidence suggests that there may be different subregions within the vOTC involved in the rapid identification of word forms. Here, we characterize vOTC reading circuitry using a multimodal approach combining functional, structural, and quantitative MRI and behavioral data. Two main word-responsive vOTC areas emerged: a posterior area involved in visual feature extraction, structurally connected to the intraparietal sulcus via the vertical occipital fasciculus; and an anterior area involved in integrating information with other regions of the language network, structurally connected to the angular gyrus via the posterior arcuate fasciculus. Furthermore, functional activation in these vOTC regions predicted reading behavior outside of the scanner. Differences in the microarchitectonic properties of gray-matter cells in these segregated areas were also observed, in line with earlier cytoarchitectonic evidence. These findings advance our understanding of the vOTC circuitry by linking functional responses to anatomical structure, revealing the pathways of distinct reading-related processes.

Cultural specialization of visual cortex

A growing body of evidence suggests culture influences how individuals perceive the world around them. This study investigates whether these cultural differences extend to a simple object viewing task and visual cortex by examining voxel pattern representations with multi-voxel pattern analysis (MVPA). During functional magnetic resonance imaging scanning, 20 East Asian and 20 American participants viewed photos of everyday items, equated for familiarity and conceptual agreement across cultures. Whole brain searchlight mapping with non-parametric statistical evaluation tested whether these stimuli evoked multi-voxel patterns that were distinct between cultural groups. We found that participants' cultural identities were successfully predicted from stimuli representations in visual cortex Brodmann areas 18 and 19. This result demonstrates culturally specialized visual cortex during a basic perceptual task ubiquitous to everyday life.

Dynamic Patterns of Brain Structure-Behavior Correlation Across the Lifespan

Although the brain/behavior correlation is one of the premises of cognitive neuroscience, there is still no consensus about the relationship between brain measures and cognitive function, and only little is known about the effect of age on this relationship. We investigated the age-associated variations on the spatial patterns of cortical thickness correlates of four cognitive domains. We showed that the spatial distribution of the cortical thickness correlates of each cognitive domain is distinctive and depicts varying age-association differences across the adult lifespan. Specifically, the present study provides evidence that distinct cognitive domains are associated with unique structural patterns in three adulthood periods: Early, middle, and late adulthood. These findings suggest a dynamic interaction between multiple neural substrates supporting each cognitive domain across the adult lifespan.

Attentional asymmetry between visual hemifields is related to habitual direction of reading and its implications for debate on cause and effects of dyslexia

A major controversy regarding dyslexia is whether any of the many visual and phonological deficits found to be correlated with reading difficulty cause the impairment or result from the reduced amount of reading done by dyslexics. We studied this question by comparing a visual capacity in the left and right visual hemifields in people habitually reading scripts written right-to-left or left-to-right. Selective visual attention is necessary for efficient visual search and also for the sequential recognition of letters in words. Because such attentional allocation during reading depends on the direction in which one is reading, asymmetries in search efficiency may reflect biases arising from the habitual direction of reading. We studied this by examining search performance in three cohorts: (a) left-to-right readers who read English fluently; (b) right-to-left readers fluent in reading Farsi but not any left-to-right script; and (c) bilingual readers fluent in English and in Farsi, Arabic, or Hebrew. Left-to-right readers showed better search performance in the right hemifield and right-to-left readers in the left hemifield, but bilingual readers showed no such asymmetries. Thus, reading experience biases search performance in the direction of reading, which has implications for the cause and effect relationships between reading and cognitive functions.

Diagnosing the Neural Circuitry of Reading

We summarize the current state of knowledge of the brain's reading circuits, and then we describe opportunities to use quantitative and reproducible methods for diagnosing these circuits. Neural circuit diagnostics-by which we mean identifying the locations and responses in an individual that differ significantly from measurements in good readers-can help parents and educators select the best remediation strategy. A sustained effort to develop and share diagnostic methods can support the societal goal of improving literacy.

Learning to read alters cortico-subcortical cross-talk in the visual system of illiterates

Learning to read is known to result in a reorganization of the developing cerebral cortex. In this longitudinal resting-state functional magnetic resonance imaging study in illiterate adults, we show that only 6 months of literacy training can lead to neuroplastic changes in the mature brain. We observed that literacy-induced neuroplasticity is not confined to the cortex but increases the functional connectivity between the occipital lobe and subcortical areas in the midbrain and the thalamus. Individual rates of connectivity increase were significantly related to the individual decoding skill gains. These findings crucially complement current neurobiological concepts of normal and impaired literacy acquisition.

Cultural Differences in Visual Search for Geometric Figures

While some studies suggest cultural differences in visual processing, others do not, possibly because the complexity of their tasks draws upon high-level factors that could obscure such effects. To control for this, we examined cultural differences in visual search for geometric figures, a relatively simple task for which the underlying mechanisms are reasonably well known. We replicated earlier results showing that North Americans had a reliable search asymmetry for line length: Search for long among short lines was faster than vice versa. In contrast, Japanese participants showed no asymmetry. This difference did not appear to be affected by stimulus density. Other kinds of stimuli resulted in other patterns of asymmetry differences, suggesting that these are not due to factors such as analytic/holistic processing but are based instead on the target-detection process. In particular, our results indicate that at least some cultural differences reflect different ways of processing early-level features, possibly in response to environmental factors.

Climbing Brain Levels of Organisation from Genes to Consciousness

Given the tremendous complexity of brain organisation, here I propose a strategy that dynamically links stages of brain organisation from genes to consciousness, at four privileged structural levels: genes; transcription factors (TFs)-gene networks; synaptic epigenesis; and long-range connectivity. These structures are viewed as nested and reciprocally inter-regulated, with a hierarchical organisation that proceeds on different timescales during the course of evolution and development. Interlevel bridging mechanisms include intrinsic variation-selection mechanisms, which offer a community of bottom-up and top-down models linking genes to consciousness in a stepwise manner.

Functional and Structural Neuroplasticity Induced by Short-Term Tactile Training Based on Braille Reading

Neuroplastic changes induced by sensory learning have been recognized within the cortices of specific modalities as well as within higher ordered multimodal areas. The interplay between these areas is not fully understood, particularly in the case of somatosensory learning. Here we examined functional and structural changes induced by short-term tactile training based of Braille reading, a task that requires both significant tactile expertise and mapping of tactile input onto multimodal representations. Subjects with normal vision were trained for 3 weeks to read Braille exclusively by touch and scanned before and after training, while performing a same-different discrimination task on Braille characters and meaningless characters. Functional and diffusion-weighted magnetic resonance imaging sequences were used to assess resulting changes. The strongest training-induced effect was found in the primary somatosensory cortex (SI), where we observed bilateral augmentation in activity accompanied by an increase in fractional anisotropy (FA) within the contralateral SI. Increases of white matter fractional anisotropy were also observed in the secondary somatosensory area (SII) and the thalamus. Outside of somatosensory system, changes in both structure and function were found in i.e., the fusiform gyrus, the medial frontal gyri and the inferior parietal lobule. Our results provide evidence for functional remodeling of the somatosensory pathway and higher ordered multimodal brain areas occurring as a result of short-lasting tactile learning, and add to them a novel picture of extensive white matter plasticity.

Visual sign phonology: insights into human reading and language from a natural soundless phonology

Among the most prevailing assumptions in science and society about the human reading process is that sound and sound-based phonology are critical to young readers. The child's sound-to-letter decoding is viewed as universal and vital to deriving meaning from print. We offer a different view. The crucial link for early reading success is not between segmental sounds and print. Instead the human brain's capacity to segment, categorize, and discern linguistic patterning makes possible the capacity to segment all languages. This biological process includes the segmentation of languages on the hands in signed languages. Exposure to natural sign language in early life equally affords the child's discovery of silent segmental units in visual sign phonology (VSP) that can also facilitate segmental decoding of print. We consider powerful biological evidence about the brain, how it builds sound and sign phonology, and why sound and sign phonology are equally important in language learning and reading. We offer a testable theoretical account, reading model, and predictions about how VSP can facilitate segmentation and mapping between print and meaning. We explain how VSP can be a powerful facilitator of all children's reading success (deaf and hearing)-an account with profound transformative impact on learning to read in deaf children with different language backgrounds. The existence of VSP has important implications for understanding core properties of all human language and reading, challenges assumptions about language and reading as being tied to sound, and provides novel insight into a remarkable biological equivalence in signed and spoken languages. WIREs Cogn Sci 2016, 7:366-381. doi: 10.1002/wcs.1404 For further resources related to this article, please visit the WIREs website.

Brain mechanisms of recovery from pure alexia: A single case study with multiple longitudinal scans

Pure alexia is an acquired reading disorder, typically due to a left occipito-temporal lesion affecting the Visual Word Form Area (VWFA). It is unclear whether the VWFA acts as a unique bottleneck for reading, or whether alternative routes are available for recovery. Here, we address this issue through the single-case longitudinal study of a neuroscientist who experienced pure alexia and participated in 17 behavioral, 9 anatomical, and 9 fMRI assessment sessions over a period of two years. The origin of the impairment was assigned to a small left fusiform lesion, accompanied by a loss of VWFA responsivity and by the degeneracy of the associated white matter pathways. fMRI experiments allowed us to image longitudinally the visual perception of words, as compared to other classes of stimuli, as well as the mechanisms of letter-by-letter reading. The progressive improvement of reading was not associated with the re-emergence of a new area selective to words, but with increasing responses in spared occipital cortex posterior to the lesion and in contralateral right occipital cortex. Those regions showed a non-specific increase of activations over time and an increase in functional correlation with distant language areas. Those results confirm the existence of an alternative occipital route for reading, bypassing the VWFA, but they also point to its key limitation: the patient remained a slow letter-by-letter reader, thus supporting the critical importance of the VWFA for the efficient parallel recognition of written words.

Chinese Character and English Word processing in children's ventral occipitotemporal cortex: fMRI evidence for script invariance

Learning to read is thought to involve the recruitment of left hemisphere ventral occipitotemporal cortex (OTC) by a process of "neuronal recycling", whereby object processing mechanisms are co-opted for reading. Under the same theoretical framework, it has been proposed that the visual word form area (VWFA) within OTC processes orthographic stimuli independent of culture and writing systems, suggesting that it is universally involved in written language. However, this "script invariance" has yet to be demonstrated in monolingual readers of two different writing systems studied under the same experimental conditions. Here, using functional magnetic resonance imaging (fMRI), we examined activity in response to English Words and Chinese Characters in 1st graders in the United States and China, respectively. We examined each group separately and found the readers of English as well as the readers of Chinese to activate the left ventral OTC for their respective native writing systems (using both a whole-brain and a bilateral OTC-restricted analysis). Critically, a conjunction analysis of the two groups revealed significant overlap between them for native writing system processing, located in the VWFA and therefore supporting the hypothesis of script invariance. In the second part of the study, we further examined the left OTC region responsive to each group's native writing system and found that it responded equally to Object stimuli (line drawings) in the Chinese-reading children. In English-reading children, the OTC responded much more to Objects than to English Words. Together, these results support the script invariant role of the VWFA and also support the idea that the areas recruited for character or word processing are rooted in object processing mechanisms of the left OTC.

Massive cortical reorganization in sighted Braille readers

The brain is capable of large-scale reorganization in blindness or after massive injury. Such reorganization crosses the division into separate sensory cortices (visual, somatosensory...). As its result, the visual cortex of the blind becomes active during tactile Braille reading. Although the possibility of such reorganization in the normal, adult brain has been raised, definitive evidence has been lacking. Here, we demonstrate such extensive reorganization in normal, sighted adults who learned Braille while their brain activity was investigated with fMRI and transcranial magnetic stimulation (TMS). Subjects showed enhanced activity for tactile reading in the visual cortex, including the visual word form area (VWFA) that was modulated by their Braille reading speed and strengthened resting-state connectivity between visual and somatosensory cortices. Moreover, TMS disruption of VWFA activity decreased their tactile reading accuracy. Our results indicate that large-scale reorganization is a viable mechanism recruited when learning complex skills.

DOI:http://dx.doi.org/10.7554/eLife.10762.001

According to most textbooks, our brain is divided into separate areas that are dedicated to specific senses. We have a visual cortex for vision, a tactile cortex for touch, and so on. However, researchers suspect that this division might not be as fixed as the textbooks say. For example, blind people can switch their 'leftover' visual cortex to non-visual purposes, such as reading Braille – a tactile alphabet.

Can this switch in functional organization also happen in healthy people with normal vision? To investigate this, Siuda-Krzywicka, Bola et al. taught a group of healthy, sighted people to read Braille by touch, and monitored the changes in brain activity that this caused using a technique called functional magnetic resonance imaging. According to textbooks, tactile reading should engage the tactile cortex. Yet, the experiment revealed that the brain activity critical for reading Braille by touch did not occur in the volunteers’ tactile cortex, but in their visual cortex.

Further experiments used a technique called transcranial magnetic stimulation to suppress the activity of the visual cortex of the volunteers. This impaired their ability to read Braille by touch. This is a clear-cut proof that sighted adults can re-program their visual cortex for non-visual, tactile purposes.

These results show that intensive training in a complex task can overcome the sensory division-of-labor of our brain. This indicates that our brain is much more flexible than previously thought, and that such flexibility might occur when we learn everyday, complex skills such as driving a car or playing a musical instrument.

The next question that follows from this work is: what enables the brain’s activity to change after learning to read Braille? To understand this, Siuda-Krzywicka, Bola et al. are currently exploring how the physical structure of the brain changes as a result of a person acquiring the ability to read Braille by touch.

DOI:http://dx.doi.org/10.7554/eLife.10762.002

Fusiform Gyrus Laterality in Writing Systems with Different Mapping Principles: An Artificial Orthography Training Study

Writing systems vary in many ways, making it difficult to account for cross-linguistic neural differences. For example, orthographic processing of Chinese characters activates the mid-fusiform gyri (mFG) bilaterally, whereas the processing of English words predominantly activates the left mFG. Because Chinese and English vary in visual processing (holistic vs. analytical) and linguistic mapping principle (morphosyllabic vs. alphabetic), either factor could account for mFG laterality differences. We used artificial orthographies representing English to investigate the effect of mapping principle on mFG lateralization. The fMRI data were compared for two groups that acquired foundational proficiency: one for an alphabetic and one for an alphasyllabic artificial orthography. Greater bilateral mFG activation was observed in the alphasyllabic versus alphabetic group. The degree of bilaterality correlated with reading fluency for the learned orthography in the alphasyllabic but not alphabetic group. The results suggest that writing systems with a syllable-based mapping principle recruit bilateral mFG to support orthographic processing. Implications for individuals with left mFG dysfunction will be discussed.

Orthographic processing deficits in developmental dyslexia: Beyond the ventral visual stream

Fast effortless reading has been associated with the Visual Word Form Area (VWFA), a region in the ventral visual stream that specializes in the recognition of letter strings. Several neuroimaging studies of dyslexia revealed an underactivation of this region. However, most of these studies used reading tasks and/or were carried out on adults. Given that fluent reading is severely impaired in dyslexics, any underactivation might simply reflect a well-established reading deficit in impaired readers and could be the consequence rather than the cause of dyslexia. Here, we designed a task that does not rely on reading per se but that tapped early visual orthographic processing that forms the basis of reading. Dyslexic children aged 8-12years and age-matched controls were asked to search for letters, digits, and symbols in 5-element strings (Experiment 1). This novel task was complemented by a classic task known to activate the VWFA, namely the passive viewing of pseudowords and falsefonts (Experiment 2). We found that in addition to significant group differences in the VWFA, dyslexic children showed a significant underactivation of the middle occipital gyrus (MOG) relative to the control group. Several areas in the MOG are known for their engagement in visuospatial processing, and it has been proposed that the MOG is necessary for ordering the symbols in unfamiliar strings. Our results suggest that the VWFA deficit might be secondary to an impairment of visuospatial processing in the MOG. We argue that efficient processing in MOG in the course of reading acquisition is critical for the development of effortless fast visual word recognition in the VWFA.

Expecting to See a Letter: Alpha Oscillations as Carriers of Top-Down Sensory Predictions

Predictions strongly influence perception. However, the neurophysiological processes that implement predictions remain underexplored. It has been proposed that high- and low-frequency neuronal oscillations act as carriers of sensory evidence and top-down predictions, respectively (von Stein and Sarnthein 2000; Bastos et al. 2012). However, evidence for the latter hypothesis remains scarce. In particular, it remains to be shown whether slow prestimulus alpha oscillations in task-relevant brain regions are stronger in the presence of predictions, whether they influence early categorization processes, and whether this interplay indeed boosts perception. Here, we directly address these questions by manipulating subjects' prior expectations about the identity of visually presented letters while collecting magnetoencephalographic recordings. We find that predictions lead to increased prestimulus alpha oscillations in a multisensory network representing grapheme/phoneme associations. Furthermore, alpha power interacts with stimulus degradation and top-down expectations to predict visibility ratings, and correlates with the amplitude of early sensory components (P1/N1m complex), suggesting a role in the selective amplification of predicted information. Our results thus indicate that low-frequency alpha oscillations can serve as a mechanism to carry and test sensory predictions about letters.