A sensitive period for language in the visual cortex: distinct patterns of plasticity in congenitally versus late blind adults

Similar Computational Hierarchies for Reading and Speech in the Occipital Cortex of Sighed and Blind: Converging Evidence from fMRI and Chronometric TMS

High-level perception results from interactions between hierarchical brain systems responsive to gradually increasing feature complexities. During reading, the initial evaluation of simple visual features in the early visual cortex (EVC) is followed by orthographic and lexical computations in the ventral occipitotemporal cortex (vOTC). While similar visual regions are engaged in tactile Braille reading in congenitally blind people, it is unclear whether the visual network maintains or reorganizes its hierarchy for reading in this population. Combining fMRI and chronometric transcranial magnetic stimulation (TMS), our study revealed a clear correspondence between sighted and blind individuals (both male and female) on how their occipital cortices functionally supports reading and speech processing. Using fMRI, we first observed that vOTC, but not EVC, showed an enhanced response to lexical vs nonlexical information in both groups and sensory modalities. Using TMS, we further found that, in both groups, the processing of written words and pseudowords was disrupted by the EVC stimulation at both early and late time windows. In contrast, the vOTC stimulation disrupted the processing of these written stimuli only when applied at late time windows, again in both groups. In the speech domain, we observed TMS effects only for meaningful words and only in the blind participants. Overall, our results suggest that, while the responses in the deprived visual areas might extend their functional response to other sensory modalities, the computational gradients between early and higher-order occipital regions are retained, at least for reading.

Visual cortical thickness increases with prolonged artificial vision restoration

The Argus II retinal prosthesis restores visual perception to late blind individuals. It has been shown that structural changes occur in the brain due to late-onset blindness, including cortical thinning in visual cortical regions. Following vision restoration, it is not yet known whether visual regions are reinvigorated and regain a normal cortical thickness or retain the diminished thickness from blindness. We evaluated the cortical thicknesses of 10 Argus II participants, 10 blind participants, and 13 sighted participants. The Argus II patients on average had a thicker left cuneus cortex and lateral occipital cortex relative to the blind patients. The duration of the Argus II use significantly partially correlated with thicker visual cortical regions in the left hemisphere. Furthermore, in the 2 case studies (scanned before and after implantation), the patient with longer device use (44.5 months) had an increase in the cortical thickness of visual regions, whereas the shorter-using patient did not (6.5 months). Overall, the Argus II participants' cortical thickness was on average significantly rejuvenated in 2 higher visual regions, and participants using the implant for a longer duration had thicker visual regions. This research raises the possibility of structural plasticity reversing visual cortical atrophy in vision restoration participants.

Visual experience affects neural correlates of audio-haptic integration: A case study of non-sighted individuals

The ability to reduce sensory uncertainty by integrating information across different senses develops late in humans and depends on cross-modal, sensory experience during childhood and adolescence. While the dependence of audio-haptic integration on vision suggests cross-modal neural reorganization, evidence for such changes is lacking. Furthermore, little is known about the neural processes underlying audio-haptic integration even in sighted adults. Here, we examined electrophysiological correlates of audio-haptic integration in sighted adults (n = 29), non-sighted adults (n = 7), and sighted adolescents (n = 12) using a data-driven electrical neuroimaging approach. In sighted adults, optimal integration performance was predicted by topographical and super-additive strength modulations around 205-285 ms. Data from four individuals who went blind before the age of 8-9 years suggests that they achieved optimal integration via different, sub-additive mechanisms at earlier processing stages. Sighted adolescents showed no robust multisensory modulations. Late-blind adults, who did not show behavioral benefits of integration, demonstrated modulations at early latencies. Our findings suggest a critical period for the development of optimal audio-haptic integration dependent on visual experience around the late childhood and early adolescence.

Neural specialization for 'visual' concepts emerges in the absence of vision

The 'different-body/different-concepts hypothesis' central to some embodiment theories proposes that the sensory capacities of our bodies shape the cognitive and neural basis of our concepts. We tested this hypothesis by comparing behavioral semantic similarity judgments and neural signatures (fMRI) of 'visual' categories ('living things,' or animals, e.g., tiger, and light events, e.g., sparkle) across congenitally blind (n = 21) and sighted (n = 22) adults. Words referring to 'visual' entities/nouns and events/verbs (animals and light events) were compared to less vision-dependent categories from the same grammatical class (animal vs. place nouns, light vs. sound, mouth, and hand verbs). Within-category semantic similarity judgments about animals (e.g., sparrow vs. finch) were partially different across groups, consistent with the idea that sighted people rely on visually learned information to make such judgments about animals. However, robust neural specialization for living things in temporoparietal semantic networks, including in the precuneus, was observed in blind and sighted people alike. For light events, which are directly accessible only through vision, behavioral judgments were indistinguishable across groups. Neural responses to light events were also similar across groups: in both blind and sighted people, the left middle temporal gyrus (LMTG+) responded more to event concepts, including light events, compared to entity concepts. Multivariate patterns of neural activity in LMTG+ distinguished among different event types, including light events vs. other event types. In sum, we find that neural signatures of concepts previously attributed to visual experience do not require vision. Across a wide range of semantic types, conceptual representations develop independent of sensory experience.

A Whole-Brain Topographic Ontology

It is a common view that the intricate array of specialized domains in the ventral visual pathway is innately prespecified. What this review postulates is that it is not. We explore the origins of domain specificity, hypothesizing that the adult brain emerges from an interplay between a domain-general map-based architecture, shaped by intrinsic mechanisms, and experience. We argue that the most fundamental innate organization of cortex in general, and not just the visual pathway, is a map-based topography that governs how the environment maps onto the brain, how brain areas interconnect, and ultimately, how the brain processes information.

The mechanism of human color vision and potential implanted devices for artificial color vision

Vision plays a major role in perceiving external stimuli and information in our daily lives. The neural mechanism of color vision is complicated, involving the co-ordinated functions of a variety of cells, such as retinal cells and lateral geniculate nucleus cells, as well as multiple levels of the visual cortex. In this work, we reviewed the history of experimental and theoretical studies on this issue, from the fundamental functions of the individual cells of the visual system to the coding in the transmission of neural signals and sophisticated brain processes at different levels. We discuss various hypotheses, models, and theories related to the color vision mechanism and present some suggestions for developing novel implanted devices that may help restore color vision in visually impaired people or introduce artificial color vision to those who need it.

The impact of early and late blindness on language and verbal working memory: A brain-constrained neural model

Neural circuits related to language exhibit a remarkable ability to reorganize and adapt in response to visual deprivation. Particularly, early and late blindness induce distinct neuroplastic changes in the visual cortex, repurposing it for language and semantic processing. Interestingly, these functional changes provoke a unique cognitive advantage - enhanced verbal working memory, particularly in early blindness. Yet, the underlying neuromechanisms and the impact on language and memory-related circuits remain not fully understood. Here, we applied a brain-constrained neural network mimicking the structural and functional features of the frontotemporal-occipital cortices, to model conceptual acquisition in early and late blindness. The results revealed differential expansion of conceptual-related neural circuits into deprived visual areas depending on the timing of visual loss, which is most prominent in early blindness. This neural recruitment is fundamentally governed by the biological principles of neural circuit expansion and the absence of uncorrelated sensory input. Critically, the degree of these changes is constrained by the availability of neural matter previously allocated to visual experiences, as in the case of late blindness. Moreover, we shed light on the implication of visual deprivation on the neural underpinnings of verbal working memory, revealing longer reverberatory neural activity in 'blind models' as compared to the sighted ones. These findings provide a better understanding of the interplay between visual deprivations, neuroplasticity, language processing and verbal working memory.

Reconsidering Luria's speech mediation: Verbalization and haptic picture identification in children with congenital total blindness

Current accounts of behavioral and neurocognitive correlates of plasticity in blindness are just beginning to incorporate the role of speech and verbal production. We assessed Vygotsky/Luria's speech mediation hypothesis, according to which speech activity can become a mediating tool for perception of complex stimuli, specifically, for encoding tactual/haptic spatial patterns which convey pictorial information (haptic pictures). We compared verbalization in congenitally totally blind (CTB) and age-matched sighted but visually impaired (VI) children during a haptic picture naming task which included two repeated, test-retest, identifications. The children were instructed to explore 10 haptic schematic pictures of objects (e.g., cup) and body parts (e.g., face) and provide (without experimenter's feedback) their typical name. Children's explorations and verbalizations were videorecorded and transcribed into audio segments. Using the Computerized Analysis of Language (CLAN) program, we extracted several measurements from the observed verbalizations, including number of utterances and words, utterance/word duration, and exploration time. Using the Word2Vec natural language processing technique we operationalized semantic content from the relative distances between the names provided. Furthermore, we conducted an observational content analysis in which three judges categorized verbalizations according to a rating scale assessing verbalization content. Results consistently indicated across all measures that the CTB children were faster and semantically more precise than their VI counterparts in the first identification test, however, the VI children reached the same level of precision and speed as the CTB children at retest. Overall, the task was harder for the VI group. Consistent with current neuroscience literature, the prominent role of speech in CTB and VI children's data suggests that an underlying cross-modal involvement of integrated brain networks, notably associated with Broca's network, likely also influenced by Braille, could play a key role in compensatory plasticity via the mediational mechanism postulated by Luria.

Developing cortex is functionally pluripotent: Evidence from blindness

How rigidly does innate architecture constrain function of developing cortex? What is the contribution of early experience? We review insights into these questions from visual cortex function in people born blind. In blindness, occipital cortices are active during auditory and tactile tasks. What 'cross-modal' plasticity tells us about cortical flexibility is debated. On the one hand, visual networks of blind people respond to higher cognitive information, such as sentence grammar, suggesting drastic repurposing. On the other, in line with 'metamodal' accounts, sighted and blind populations show shared domain preferences in ventral occipito-temporal cortex (vOTC), suggesting visual areas switch input modality but perform the same or similar perceptual functions (e.g., face recognition) in blindness. Here we bring these disparate literatures together, reviewing and synthesizing evidence that speaks to whether visual cortices have similar or different functions in blind and sighted people. Together, the evidence suggests that in blindness, visual cortices are incorporated into higher-cognitive (e.g., fronto-parietal) networks, which are a major source long-range input to the visual system. We propose the connectivity-constrained experience-dependent account. Functional development is constrained by innate anatomical connectivity, experience and behavioral needs. Infant cortex is pluripotent, the same anatomical constraints develop into different functional outcomes.

The role of the left ventral occipitotemporal cortex in speech processing-The influence of visual deprivation

The role of the left ventral occipitotemporal cortex (vOT) in reading is well-established in both sighted and blind readers. Its role in speech processing remains only partially understood. Here, we test the involvement of the left vOT in phonological processing of spoken language in the blind (N = 50, age: 6.76-60.32) and in the sighted (N = 54, age: 6.79-59.83) by means of whole-brain and region-of-interest (including individually identified) fMRI analyses. We confirm that the left vOT is sensitive to phonological processing (shows greater involvement in rhyming compared to control spoken language task) in both blind and sighted participants. However, in the sighted, the activation was observed only during the rhyming task and in the speech-specific region of the left vOT, pointing to task and modality specificity. In contrast, in the blind group, the left vOT was active during speech processing irrespective of task and in both speech and reading-specific vOT regions. Only in the blind, the left vOT presented a higher degree of sensitivity to phonological processing than other language nodes in the left inferior frontal and superior temporal cortex. Our results suggest a changed development of the left vOT sensitivity to spoken language, resulting from visual deprivation.

Embodied language of emotions: Predicting human intuitions with linguistic distributions in blind and sighted individuals

Recent constructionist theories have suggested that language and sensory experience play a crucial role not only in how individuals categorise emotions but also in how they experience and shape them, helping to acquire abstract concepts that are used to make sense of bodily perceptions associated with specific emotions. Here, we aimed to investigate the role of sensory experience in conceptualising bodily felt emotions by asking 126 Italian blind participants to freely recall in which part of the body they commonly feel specific emotions (N = 15). Participants varied concerning visual experience in terms of blindness onset (i.e., congenital vs late) and degree of visual experience (i.e., total vs partial sensory loss). Using an Italian semantic model to estimate to what extent discrete emotions are associated with body parts in language experience, we found that all participants' reports correlated with the model predictions. Interestingly, blind - and especially congenitally blind - participants' responses were more strongly correlated with the model, suggesting that language might be one of the possible compensative mechanisms for the lack of visual feedback in constructing bodily felt emotions. Our findings present theoretical implications for the study of emotions, as well as potential real-world applications for blind individuals, by revealing, on the one hand, that vision plays an essential role in the construction of felt emotions and the way we talk about our related bodily (emotional) experiences. On the other hand, evidence that blind individuals rely more strongly on linguistic cues suggests that vision is a strong cue to acquire emotional information from the surrounding world, influencing how we experience emotions. While our findings do not suggest that blind individuals experience emotions in an atypical and dysfunctional way, they nonetheless support the view that promoting the use of non-visual emotional signs and body language since early on might help the blind child to develop a good emotional awareness as well as good emotion regulation abilities.

Articulation-Function-Associated Cortical Developmental Changes in Patients with Cleft Lip and Palate

Cleft lip and palate (CLP) is one of the most common craniofacial malformations. Overall, 40–80% of CLP patients have varying degrees of articulation problems after palatoplasty. Previous studies revealed abnormal articulation-related brain function in CLP patients. However, the association between articulation disorders and cortical structure development in CLP patients remains unclear. Twenty-six CLP adolescents (aged 5–14 years; mean 8.88 years; female/male 8/18), twenty-three CLP adults (aged 18–35 years; mean 23.35 years; female/male 6/17), thirty-seven healthy adolescents (aged 5–16 years; mean 9.89 years; female/male 5/16), and twenty-two healthy adults (aged 19–37 years; mean 24.41 years; female/male 19/37) took part in the experiment. The current study aims to investigate developmental changes in cortical structures in CLP patients with articulation disorders using both structural and functional magnetic resonance imaging (MRI). Our results reveal the distinct distribution of abnormal cortical structures in adolescent and adult CLP patients. We also found that the developmental pattern of cortical structures in CLP patients differed from the pattern in healthy controls (delayed cortical development in the left lingual gyrus (t = 4.02, cluster-wise p < 0.05), inferior temporal cortex (z = −4.36, cluster-wise p < 0.05) and right precentral cortex (t = 4.19, cluster-wise p < 0.05)). Mediation analysis identified the cortical thickness of the left pericalcarine cortex as the mediator between age and articulation function (partial mediation effect (a*b = −0.48), 95% confident interval (−0.75, −0.26)). In conclusion, our results demonstrate an abnormal developmental pattern of cortical structures in CLP patients, which is directly related to their articulation disorders.

Diverging patterns of plasticity in the nucleus basalis of Meynert in early- and late-onset blindness

Plasticity in the brain is impacted by an individual's age at the onset of the blindness. However, what drives the varying degrees of plasticity remains largely unclear. One possible explanation attributes the mechanisms for the differing levels of plasticity to the cholinergic signals originating in the nucleus basalis of Meynert. This explanation is based on the fact that the nucleus basalis of Meynert can modulate cortical processes such as plasticity and sensory encoding through its widespread cholinergic projections. Nevertheless, there is no direct evidence indicating that the nucleus basalis of Meynert undergoes plastic changes following blindness. Therefore, using multiparametric magnetic resonance imaging, we examined if the structural and functional properties of the nucleus basalis of Meynert differ between early blind, late blind and sighted individuals. We observed that early and late blind individuals had a preserved volumetric size and cerebrovascular reactivity in the nucleus basalis of Meynert. However, we observed a reduction in the directionality of water diffusion in both early and late blind individuals compared to sighted individuals. Notably, the nucleus basalis of Meynert presented diverging patterns of functional connectivity between early and late blind individuals. This functional connectivity was enhanced at both global and local (visual, language and default-mode networks) levels in the early blind individuals, but there were little-to-no changes in the late blind individuals when compared to sighted controls. Furthermore, the age at onset of blindness predicted both global and local functional connectivity. These results suggest that upon reduced directionality of water diffusion in the nucleus basalis of Meynert, cholinergic influence may be stronger for the early blind compared to the late blind individuals. Our findings are important to unravelling why early blind individuals present stronger and more widespread cross-modal plasticity compared to late blind individuals.

Impact of blindness onset on the representation of sound categories in occipital and temporal cortices

The ventral occipito-temporal cortex (VOTC) reliably encodes auditory categories in people born blind using a representational structure partially similar to the one found in vision (Mattioni et al.,2020). Here, using a combination of uni- and multivoxel analyses applied to fMRI data, we extend our previous findings, comprehensively investigating how early and late acquired blindness impact on the cortical regions coding for the deprived and the remaining senses. First, we show enhanced univariate response to sounds in part of the occipital cortex of both blind groups that is concomitant to reduced auditory responses in temporal regions. We then reveal that the representation of the sound categories in the occipital and temporal regions is more similar in blind subjects compared to sighted subjects. What could drive this enhanced similarity? The multivoxel encoding of the 'human voice' category that we observed in the temporal cortex of all sighted and blind groups is enhanced in occipital regions in blind groups , suggesting that the representation of vocal information is more similar between the occipital and temporal regions in blind compared to sighted individuals. We additionally show that blindness does not affect the encoding of the acoustic properties of our sounds (e.g. pitch, harmonicity) in occipital and in temporal regions but instead selectively alter the categorical coding of the voice category itself. These results suggest a functionally congruent interplay between the reorganization of occipital and temporal regions following visual deprivation, across the lifespan.

Naturalistic stimuli reveal a sensitive period in cross modal responses of visual cortex: Evidence from adult-onset blindness

How do life experiences impact cortical function? In people who are born blind, the "visual" cortices are recruited during nonvisual tasks, such as Braille reading and sound localization. Do visual cortices have a latent capacity to respond to nonvisual information throughout the lifespan? Alternatively, is there a sensitive period of heightened plasticity that makes visual cortex repurposing especially possible during childhood? To gain insight into these questions, we leveraged meaningful naturalistic auditory stimuli to simultaneously engage a broad range of cognitive domains and quantify cross-modal responses across congenitally blind (n = 22), adult-onset blind (vision loss >18 years-of-age, n = 14) and sighted (n = 22) individuals. During fMRI scanning, participants listened to two types of meaningful naturalistic auditory stimuli: excerpts from movies and a spoken narrative. As controls, participants heard the same narrative with the sentences shuffled and the narrative played backwards (i.e., meaningless sounds). We correlated the voxel-wise timecourses of different participants within condition and group. For all groups, all stimulus conditions induced synchrony in auditory cortex while only the narrative stimuli synchronized responses in higher-cognitive fronto-parietal and temporal regions. As previously reported, inter-subject synchrony in visual cortices was higher in congenitally blind than sighted blindfolded participants and this between-group difference was particularly pronounced for meaningful stimuli (movies and narrative). Critically, visual cortex synchrony was no higher in adult-onset blind than sighted blindfolded participants and did not increase with blindness duration. Sensitive period plasticity enables cross-modal repurposing in visual cortices.

Inflammatory Subtypes in Antipsychotic-Naïve First-Episode Schizophrenia are Associated with Altered Brain Morphology and Topological Organization

BACKGROUND

Peripheral inflammation is implicated in schizophrenia, however, not all individuals demonstrate inflammatory alterations. Recent studies identified inflammatory subtypes in chronic psychosis with high inflammation having worse cognitive performance and displaying neuroanatomical enlargement compared to low inflammation subtypes. It is unclear if inflammatory subtypes exist earlier in the disease course, thus, we aim to identify inflammatory subtypes in antipsychotic naïve First-Episode Schizophrenia (FES).

METHODS

12 peripheral inflammatory markers, clinical, cognitive, and neuroanatomical measures were collected from a naturalistic study of antipsychotic-naïve FES patients. A combination of unsupervised principal component analysis and hierarchical clustering was used to categorize inflammatory subtypes from their cytokine data (17 FES High, 30 FES Low, and 33 healthy controls (HCs)). Linear regression analysis was used to assess subtype differences. Neuroanatomical correlations with clinical and cognitive measures were performed using partial Spearman correlations. Graph theoretical analyses were performed to assess global and local network properties across inflammatory subtypes.

RESULTS

The FES High group made up 36% of the FES group and demonstrated significantly greater levels of IL1β, IL6, IL8, and TNFα compared to FES Low, and higher levels of IL1β and IL8 compared to HCs. FES High had greater right parahippocampal, caudal anterior cingulate, and bank superior sulcus thicknesses compared to FES Low. Compared to HCs, FES Low showed smaller bilateral amygdala volumes and widespread cortical thickness. FES High and FES Low groups demonstrated less efficient topological organization compared to HCs. Individual cytokines and/or inflammatory signatures were positively associated with cognition and symptom measures.

CONCLUSIONS

Inflammatory subtypes are present in antipsychotic-naïve FES and are associated with inflammation-mediated cortical expansion. These findings support our previous findings in chronic psychosis and point towards a connection between inflammation and blood-brain barrier disruption. Thus, identifying inflammatory subtypes may provide a novel therapeutic avenue for biomarker-guided treatment involving anti-inflammatory medications.

Desynchronized white matter function and structure in drug-naive first-episode major depressive disorder patients

BACKGROUND

Major depressive disorder (MDD) is a highly prevalent mental disease. Using magnetic resonance imaging (MRI), although numerous studies have revealed the alterations in structure and function of grey matter (GM), few studies focused on the synchronization of white matter (WM) structure and function in MDD. The aim of this study was to investigate whether functional and structural abnormalities of WM play an essential role in the neurobiological mechanisms of MDD.

METHODS

Gradient-echo imaging sequences at 3.0T were used to gather resting state functional MRI (rsfMRI) data, which were performed on 33 drug-naive first-episode MDD patients and 34 healthy controls (HCs). After data preprocessed, amplitude of low frequency fluctuation (ALFF) of WM was calculated. ALFF values in different frequency bands were analyzed, including typical (0.01-0.15 Hz) band, slow-4 (0.027-0.073 Hz) and slow-5 (0.01-0.027 Hz) bands. In addition, the fractional anisotropy (FA) values in WM in 23 patients and 26 HCs were examined using tract-based spatial statistics (TBSS) and tractography based on diffusion tensor imaging (DTI). Pearson correlation analysis was applied to analyze the relationships between ALFF values and Hamilton Depression Scale (HAMD) and Hamilton Anxiety Scale (HAMA).

RESULTS

Compared with the HCs, MDD patients showed decreased ALFF values in posterior thalamic radiation (PTR) and superior longitudinal fasciculus (SLF) in slow-5 frequency band, no significant differences of ALFF values were found in typical and slow-4 frequency bands. In addition, there were no significant differences in FA values with TBSS analysis as well as the number of fibers in PTR and SLF with tractography analysis between two groups. Further correlation analysis showed that the ALFF value in SLF was negatively correlated with HAMA-2 score (r = -0.548, p _FDR = 0.037) in patients.

CONCLUSION

Our results indicated that WM dysfunction may be associated with the pathophysiological mechanism of depression. Our study also suggested that the functional damage of the WM may precedes the structural damage in first-episode MDD patients. Furthermore, for mental disorders, slow-5 frequency band may be a more sensitive functional indicator for early detection of abnormal spontaneous brain activity in WM.

Cortical morphometric correlational networks associated with cognitive deficits in first episode schizophrenia

Schizophrenia (SCZ) is a chronic cognitive and behavioral disorder associated with abnormal cortical activity during information processing. Several brain structures associated with the seven performance domains evaluated using the MATRICS (Measurement and Treatment Research to Improve Cognition in Schizophrenia) Consensus Cognitive Battery (MCCB) have shown cortical volume loss in first episode schizophrenia (FES) patients. However, the relationship between morphological organization and MCCB performance remains unclear. Therefore, in the current observational study, high-resolution structural MRI scans were collected from 50 FES patients, and the morphometric correlation network (MCN) using cortical volume was established to characterize the cortical pattern associated with poorer MCCB performance. We also investigated topological properties, such as the modularity, the degree and the betweenness centrality. Our findings show structural volume was directly and strongly associated with the cognitive deficits of FES patients in the precuneus, anterior cingulate, and fusiform gyrus, as well as the prefrontal, parietal, and sensorimotor cortices. The medial orbitofrontal, fusiform, and superior frontal gyri were not only identified as the predominant nodes with high degree and betweenness centrality in the MCN, but they were also found to be critical in performance in several of the MCCB domains. Together, these results suggest a widespread cortical network is altered in FES patients and that performance on the MCCB domains is associated with the core pathophysiology of SCZ.

Investigating the neurochemistry of the human visual system using magnetic resonance spectroscopy

Biochemical processes underpin the structure and function of the visual cortex, yet our understanding of the fundamental neurochemistry of the visual brain is incomplete. Proton magnetic resonance spectroscopy (¹H-MRS) is a non-invasive brain imaging tool that allows chemical quantification of living tissue by detecting minute differences in the resonant frequency of molecules. Application of MRS in the human brain in vivo has advanced our understanding of how the visual brain consumes energy to support neural function, how its neural substrates change as a result of disease or dysfunction, and how neural populations signal during perception and plasticity. The aim of this review is to provide an entry point to researchers interested in investigating the neurochemistry of the visual system using in vivo measurements. We provide a basic overview of MRS principles, and then discuss recent findings in four topics of vision science: (i) visual perception, plasticity in the (ii) healthy and (iii) dysfunctional visual system, and (iv) during visual stimulation. Taken together, evidence suggests that the neurochemistry of the visual system provides important novel insights into how we perceive the world.

Reduced Functional Connectivity in Children With Congenital Cataracts Using Resting-State Electroencephalography Measurement

Objectives

Numerous task-based functional magnetic resonance imaging studies indicate the presence of compensatory functional improvement in patients with congenital cataracts. However, there is neuroimaging evidence that shows decreased sensory perception or cognition information processing related to visual dysfunction, which favors a general loss hypothesis. This study explored the functional connectivity between visual and other networks in children with congenital cataracts using resting state electroencephalography.

Methods

Twenty-one children with congenital cataracts (age: 8.02 ± 2.03 years) and thirty-five sex- and age-matched normal sighted controls were enrolled to investigate functional connectivity between the visual cortex and the default mode network, the salience network, and the cerebellum network during resting state electroencephalography (eyes closed) recordings.

Result

The congenital cataract group was less active, than the control group, in the occipital, temporal, frontal and limbic lobes in the theta, alpha, beta1 and beta2 frequency bands. Additionally, there was reduced alpha-band connectivity between the visual and somatosensory cortices and between regions of the frontal and parietal cortices associated with cognitive and attentive control.

Conclusion

The results indicate abnormalities in sensory, cognition, motion and execution functional connectivity across the developing brains of children with congenital cataracts when compared with normal controls. Reduced frontal alpha activity and alpha-band connectivity between the visual cortex and salience network might reflect attenuated inhibitory information flow, leading to higher attentional states, which could contribute to adaptation of environmental change in this group of patients.

Substance use initiation and the prediction of subsequent academic achievement

Academic performance significantly influences educational advancement, career opportunities, and life outcomes. The extent to which adolescent substance use and brain morphology predict academic achievement has not been extensively explored. We examined grade point average (GPA) at the time alcohol and cannabis use often starts (7th - 9th grade) and subsequently during 11th and 12th grade in a 170 physically healthy adolescents in a longitudinal study. Covariance analysis examined predictive features from 36 metrics of middle school academic performance and initiation of alcohol and cannabis use. Using a machine learning approach, GPA from 7th, 8th, and 9th grade strongly predicted 11th and 12th grade GPA, followed in predictive power by alcohol use age of onset. A machine learning approach determined 16 (from 336) baseline neuroimaging features that reflected lower thickness, area, or volume in average high school GPA drinkers compared to nondrinkers. Features that distinguished average performing drinkers from nondrinkers suggested accelerated gray matter loss during adolescence for drinkers, while high performing drinkers compared to nondrinkers may have attenuated gray matter maturation. Additional possibilities are discussed.

The Effect of Congenital and Acquired Bilateral Anophthalmia on Brain Structure

The aim of this study was to compare the pattern of changes in brain structure resulting from congenital and acquired bilateral anophthalmia. Brain structure was investigated using 3T magnetic resonance imaging (MRI) in Oxford (congenital) or Manchester (acquired). T1-weighted structural and diffusion-weighted scans were acquired from people with anophthalmia and sighted control participants. Differences in grey matter between the groups were quantified using voxel-based morphometry and differences in white matter microstructure using tract-based spatial statistics. Quantification of optic nerve volume and cortical thickness in visual regions was also performed in all groups. The optic nerve was reduced in volume in both anophthalmic populations, but to a greater extent in the congenital group and anophthalmia acquired at an early age. A similar pattern was found for the white matter microstructure throughout the occipitotemporal regions of the brain, suggesting a greater reduction of integrity with increasing duration of anophthalmia. In contrast, grey matter volume changes differed between the two groups, with the acquired anophthalmia group showing a decrease in the calcarine sulcus, corresponding to the area that would have been peripheral primary visual cortex. In contrast, the acquired anophthalmia group showed a decrease in grey matter volume in the calcarine sulcus corresponding to the area that would have been peripheral primary visual cortex. There are both qualitative and quantitative differences in structural brain changes in congenital and acquired anophthalmia, indicating differential effects of development and degeneration.

Neural network for Braille reading and the speech-reading convergence in the blind: Similarities and differences to visual reading

All writing systems represent units of spoken language. Studies on the neural correlates of reading in different languages show that this skill relies on access to brain areas dedicated to speech processing. Speech-reading convergence onto a common perisylvian network is therefore considered universal among different writing systems. Using fMRI, we test whether this holds true also for tactile Braille reading in the blind. The neural networks for Braille and visual reading overlapped in the left ventral occipitotemporal (vOT) cortex. Even though we showed similar perisylvian specialization for speech in both groups, blind subjects did not engage this speech system for reading. In contrast to the sighted, speech-reading convergence in the blind was absent in the perisylvian network. Instead, the blind engaged vOT not only in reading but also in speech processing. The involvement of the vOT in speech processing and its engagement in reading in the blind suggests that vOT is included in a modality independent language network in the blind, also evidenced by functional connectivity results. The analysis of individual speech-reading convergence suggests that there may be segregated neuronal populations in the vOT for speech processing and reading in the blind.

Sensitive periods in cortical specialization for language: insights from studies with Deaf and blind individuals

Studies with Deaf and blind individuals demonstrate that linguistic and sensory experiences during sensitive periods have potent effects on neurocognitive basis of language. Native users of sign and spoken languages recruit similar fronto-temporal systems during language processing. By contrast, delays in sign language access impact proficiency and the neural basis of language. Analogously, early but not late-onset blindness modifies the neural basis of language. People born blind recruit 'visual' areas during language processing, show reduced left-lateralization of language and enhanced performance on some language tasks. Sensitive period plasticity in and outside fronto-temporal language systems shapes the neural basis of language.

V1 Projection Zone Signals in Human Macular Degeneration Depend on Task Despite Absence of Visual Stimulus

Identifying the plastic and stable components of the visual cortex after retinal loss is an important topic in visual neuroscience and neuro-ophthalmology.^1-5 Humans with juvenile macular degeneration (JMD) show significant blood-oxygen-level-dependent (BOLD) responses in the primary visual area (V1) lesion projection zone (LPZ),⁶ despite the absence of the feedforward signals from the degenerated retina. Our previous study⁷ reported that V1 LPZ responds to full-field visual stimuli during the one-back task (OBT), not during passive viewing, suggesting the involvement of task-related feedback signals. Aiming to clarify whether visual inputs to the intact retina are necessary for the LPZ responses, here, we measured BOLD responses to tactile and auditory stimuli for both JMD patients and control participants with and without OBT. Participants were instructed to close their eyes during the experiment for the purpose of eliminating retinal inputs. Without OBT, no V1 responses were detected in both groups of participants. With OBT, to the contrary, both stimuli caused substantial V1 responses in JMD patients, but not controls. Furthermore, we also found that the task-dependent activity in V1 LPZ became less pronounced when JMD patients opened their eyes, suggesting that task-related feedback signals can be partially suppressed by residual feedforward signals. Modality-independent V1 LPZ responses only in the task condition suggest that V1 LPZ responses reflect task-related feedback signals rather than reorganized feedforward visual inputs.

Adversarial brain multiplex prediction from a single brain network with application to gender fingerprinting

Brain connectivity networks, derived from magnetic resonance imaging (MRI), non-invasively quantify the relationship in function, structure, and morphology between two brain regions of interest (ROIs) and give insights into gender-related connectional differences. However, to the best of our knowledge, studies on gender differences in brain connectivity were limited to investigating pairwise (i.e., low-order) relationships across ROIs, overlooking the complex high-order interconnectedness of the brain as a network. A few recent works on neurological disorders addressed this limitation by introducing the brain multiplex which is composed of a source network intra-layer, a target intra-layer, and a convolutional interlayer capturing the high-level relationship between both intra-layers. However, brain multiplexes are built from at least two different brain networks hindering their application to connectomic datasets with single brain networks (e.g., functional networks). To fill this gap, we propose Adversarial Brain Multiplex Translator (ABMT), the first work for predicting brain multiplexes from a source network using geometric adversarial learning to investigate gender differences in the human brain. Our framework comprises: (i) a geometric source to target network translator mimicking a U-Net architecture with skip connections, (ii) a conditional discriminator which distinguishes between predicted and ground truth target intra-layers, and finally (iii) a multi-layer perceptron (MLP) classifier which supervises the prediction of the target multiplex using the subject class label (e.g., gender). Our experiments on a large dataset demonstrated that predicted multiplexes significantly boost gender classification accuracy compared with source networks and unprecedentedly identify both low and high-order gender-specific brain multiplex connections. Our ABMT source code is available on GitHub at https://github.com/basiralab/ABMT.

Sensitive Period for Cognitive Repurposing of Human Visual Cortex

Studies of sensory loss are a model for understanding the functional flexibility of human cortex. In congenital blindness, subsets of visual cortex are recruited during higher-cognitive tasks, such as language and math tasks. Is such dramatic functional repurposing possible throughout the lifespan or restricted to sensitive periods in development? We compared visual cortex function in individuals who lost their vision as adults (after age 17) to congenitally blind and sighted blindfolded adults. Participants took part in resting-state and task-based fMRI scans during which they solved math equations of varying difficulty and judged the meanings of sentences. Blindness at any age caused "visual" cortices to synchronize with specific frontoparietal networks at rest. However, in task-based data, visual cortices showed regional specialization for math and language and load-dependent activity only in congenital blindness. Thus, despite the presence of long-range functional connectivity, cognitive repurposing of human cortex is limited by sensitive periods.

Reduced perceptual narrowing in synesthesia

Synesthesia is a neurologic trait in which specific inducers, such as sounds, automatically elicit additional idiosyncratic percepts, such as color (thus "colored hearing"). One explanation for this trait-and the one tested here-is that synesthesia results from unusually weak pruning of cortical synaptic hyperconnectivity during early perceptual development. We tested the prediction from this hypothesis that synesthetes would be superior at making discriminations from nonnative categories that are normally weakened by experience-dependent pruning during a critical period early in development-namely, discrimination among nonnative phonemes (Hindi retroflex /d̪a/ and dental /ɖa/), among chimpanzee faces, and among inverted human faces. Like the superiority of 6-mo-old infants over older infants, the synesthetic groups were significantly better than control groups at making all the nonnative discriminations across five samples and three testing sites. The consistent superiority of the synesthetic groups in making discriminations that are normally eliminated during infancy suggests that residual cortical connectivity in synesthesia supports changes in perception that extend beyond the specific synesthetic percepts, consistent with the incomplete pruning hypothesis.

A sensitive period in the neural phenotype of language in blind individuals

Congenital blindness modifies the neural basis of language: "visual" cortices respond to linguistic information, and fronto-temporal language networks are less left-lateralized. We tested the hypothesis that this plasticity follows a sensitive period by comparing the neural basis of sentence processing between adult-onset blind (AB, n = 16), congenitally blind (CB, n = 22) and blindfolded sighted adults (n = 18). In Experiment 1, participants made semantic judgments for spoken sentences and, in a control condition, solved math equations. In Experiment 2, participants answered "who did what to whom" yes/no questions for grammatically complex (with syntactic movement) and simpler sentences. In a control condition, participants performed a memory task with non-words. In both experiments, visual cortices of CB and AB but not sighted participants responded more to sentences than control conditions, but the effect was much larger in the CB group. Only the "visual" cortex of CB participants responded to grammatical complexity. Unlike the CB group, the AB group showed no reduction in left-lateralization of fronto-temporal language network, relative to the sighted. These results suggest that congenital blindness modifies the neural basis of language differently from adult-onset blindness, consistent with a developmental sensitive period hypothesis.

Neuroplasticity in cerebral visual impairment (CVI): Assessing functional vision and the neurophysiological correlates of dorsal stream dysfunction

Cerebral visual impairment (CVI) results from perinatal injury to visual processing structures and pathways and is the most common individual cause of pediatric visual impairment and blindness in developed countries. While there is mounting evidence demonstrating extensive neuroplastic reorganization in early onset, profound ocular blindness, how the brain reorganizes in the setting of congenital damage to cerebral (i.e. retro-geniculate) visual pathways remains comparatively poorly understood. Individuals with CVI exhibit a wide range of visual deficits and, in particular, present with impairments of higher order visual spatial processing (referred to as "dorsal stream dysfunction") as well as object recognition (associated with processing along the ventral stream). In this review, we discuss the need for ongoing work to develop novel, neuroscience-inspired approaches to investigate functional visual deficits in this population. We also outline the role played by advanced structural and functional neuroimaging in helping to elucidate the underlying neurophysiology of CVI, and highlight key differences with regard to patterns of neural reorganization previously described in ocular blindness.

A conceptual framework for plasticity in the developing brain

In this chapter, we highlight the various definitions of early brain plasticity commonly used in the scientific literature. We then present a conceptual framework of early brain plasticity that focuses on plasticity at the level of the synapse (synaptic plasticity) and the level of the network (connectivity). The proposed framework is organized around three main domains through which current theories and principles of early brain plasticity can be integrated: (1) the mechanisms of plasticity and constraints at the synaptic level and network connectivity, (2) the importance of temporal considerations related to the development of the immature brain, and (3) the functions early brain plasticity serve. We then apply this framework to discuss some clinical disorders caused by and/or associated with impaired plasticity mechanisms. We propose that a careful examination of the relationship between mechanisms, constraints, and functions of early brain plasticity in health and disease may provide an integrative understanding of the current theories and principles generated by experimental and observational studies.

Influence of Visual Deprivation on Auditory Spectral Resolution, Temporal Resolution, and Speech Perception

We evaluated whether blind subjects have advantages in auditory spectral resolution, temporal resolution, and speech perception in noise compared with sighted subjects. We also compared psychoacoustic performance between early blind (EB) subjects and late blind (LB) subjects. Nineteen EB subjects, 16 LB subjects, and 20 sighted individuals were enrolled. All subjects were right-handed with normal and symmetric hearing thresholds and without cognitive impairments. Three psychoacoustic measurements of the subjects’ right ears were performed via an inserted earphone to determine spectral-ripple discrimination (SRD), temporal modulation detection (TMD), and speech recognition threshold (SRT) in noisy conditions. Acoustic change complex (ACC) responses were recorded during passive listening to standard ripple-inverted ripple stimuli. EB subjects exhibited better SRD than did LB (p = 0.020) and sighted (p = 0.003) subjects. TMD was better in EB (p < 0.001) and LB (p = 0.007) subjects compared with sighted subjects. SRD was positively correlated with the duration of blindness (r = 0.386, p = 0.024). Acoustic change complex data for ripple noise change at the Cz and Fz electrodes showed trends toward significant correlations with the behavioral results. In conclusion, compared with sighted subjects, EB subjects showed advantages in terms of auditory spectral and temporal resolution, while LB subjects showed an advantage in temporal resolution exclusively. These findings suggest that it might take longer for auditory spectral resolution to functionally enhance following visual deprivation compared to temporal resolution. Alternatively, a critical period of very young age may be required for auditory spectral resolution to improve following visual deprivation.

Alterations of the Brain Microstructure and Corresponding Functional Connectivity in Early-Blind Adolescents

Although evidence from studies on blind adults indicates that visual deprivation early in life leads to structural and functional disruption and reorganization of the brain, whether young blind people show similar patterns remains unknown. Therefore, this study is aimed at exploring the structural and functional alterations of the brain of early-blind adolescents (EBAs) compared to normal-sighted controls (NSCs) and investigating the effects of residual light perception on brain microstructure and function in EBAs. We obtained magnetic resonance imaging (MRI) data from 23 EBAs (8 with residual light perception (LPs), 15 without light perception (NLPs)) and 21 NSCs (age range 11-19 years old). Whole-brain voxel-based analyses of diffusion tensor imaging metrics and region-of-interest analyses of resting-state functional connectivity (RSFC) were performed to compare patterns of brain microstructure and the corresponding RSFC between the groups. The results showed that structural disruptions of LPs and NLPs were mainly located in the occipital visual pathway. Compared with NLPs, LPs showed increased fractional anisotropy (FA) in the superior frontal gyrus and reduced diffusivity in the caudate nucleus. Moreover, the correlations between FA of the occipital cortices or mean diffusivity of the lingual gyrus and age were consistent with the development trajectory of the brain in NSCs, but inconsistent or even opposite in EBAs. Additionally, we found functional, but not structural, reorganization in NLPs compared with NSCs, suggesting that functional neuroplasticity occurs earlier than structural neuroplasticity in EBAs. Altogether, these findings provided new insights into the mechanisms underlying the neural reorganization of the brain in adolescents with early visual deprivation.

Impact of years of blindness on neural circuits underlying auditory spatial representation

Early visual deprivation impacts negatively on spatial bisection abilities. Recently, an early (50-90 ms) ERP response, selective for sound position in space, has been observed in the visual cortex of sighted individuals during the spatial but not the temporal bisection task. Here, we clarify the role of vision on spatial bisection abilities and neural correlates by studying late blind individuals. Results highlight that a shorter period of blindness is linked to a stronger contralateral activation in the visual cortex and a better performance during the spatial bisection task. Contrarily, not lateralized visual activation and lower performance are observed in individuals with a longer period of blindness. To conclude, the amount of time spent without vision may gradually impact on neural circuits underlying the construction of spatial representations in late blind participants. These findings suggest a key relationship between visual deprivation and auditory spatial abilities in humans.

Differences in Emotion Recognition From Body and Face Cues Between Deaf and Hearing Individuals

Deaf individuals may compensate for the lack of the auditory input by showing enhanced capacities in certain visual tasks. Here we assessed whether this also applies to recognition of emotions expressed by bodily and facial cues. In Experiment 1, we compared deaf participants and hearing controls in a task measuring recognition of the six basic emotions expressed by actors in a series of video-clips in which either the face, the body, or both the face and body were visible. In Experiment 2, we measured the weight of body and face cues in conveying emotional information when intense genuine emotions are expressed, a situation in which face expressions alone may have ambiguous valence. We found that deaf individuals were better at identifying disgust and fear from body cues (Experiment 1) and in integrating face and body cues in case of intense negative genuine emotions (Experiment 2). Our findings support the capacity of deaf individuals to compensate for the lack of the auditory input enhancing perceptual and attentional capacities in the spared modalities, showing that this capacity extends to the affective domain.

Cortical phase locking to accelerated speech in blind and sighted listeners prior to and after training

Cross-correlation of magnetoencephalography (MEG) with time courses derived from the speech signal has shown differences in phase-locking between blind subjects able to comprehend accelerated speech and sighted controls. The present training study contributes to disentangle the effects of blindness and training. Both subject groups (baseline: n = 16 blind, 13 sighted; trained: 10 blind, 3 sighted) were able to enhance speech comprehension up to ca. 18 syllables per second. MEG responses phase-locked to syllable onsets were captured in five pre-defined source locations comprising left and right auditory cortex (A1), right visual cortex (V1), left inferior frontal gyrus (IFG) and left pre-supplementary motor area. Phase locking in A1 was consistently increased while V1 showed opposite training effects in blind and sighted subjects. Also the IFG showed some group differences indicating enhanced top-down strategies in sighted subjects while blind subjects may have a more fine-grained bottom-up resolution for accelerated speech.

Brain (re)organization following visual loss

The study of the neural consequences of sensory loss provides a unique window into the brain's functional and organizational principles. Although the blind visual cortex has been implicated in the cross-modal processing of nonvisual inputs for quite some time, recent research has shown that certain cortical organizational principles are preserved even in the case of complete sensory loss. Furthermore, a growing body of work has shown that markers of neuroplasticity extend to neuroanatomical metrics that include cortical thickness and myelinization. Although our understanding of the mechanisms that underlie sensory deprivation-driven cross-modal plasticity is improving, several critical questions remain unanswered. The specific pathways that underlie the rerouting of nonvisual information, for instance, have not been fully elucidated. The fact that important cross-modal recruitment occurs following transient deprivation in sighted individuals suggests that significant rewiring following blindness may not be required. Furthermore, there are marked individual differences regarding the magnitude and functional relevance of the cross-modal reorganization. It is also not clear to what extent precise environmental factors may play a role in establishing the degree of reorganization across individuals, as opposed to factors that might specifically relate to the cause or the nature of the visual loss. In sum, although many unresolved questions remain, sensory deprivation continues to be an excellent model for studying the plastic nature of the brain. This article is categorized under: Psychology > Brain Function and Dysfunction Psychology > Perception and Psychophysics Neuroscience > Plasticity.

On the role of visual experience in mathematical development: Evidence from blind mathematicians

Advanced mathematical reasoning, regardless of domain or difficulty, activates a reproducible set of bilateral brain areas including intraparietal, inferior temporal and dorsal prefrontal cortex. The respective roles of genetics, experience and education in the development of this math-responsive network, however, remain unresolved. Here, we investigate the role of visual experience by studying the exceptional case of three professional mathematicians who were blind from birth (n = 1) or became blind during childhood (n = 2). Subjects were scanned with fMRI while they judged the truth value of spoken mathematical and nonmathematical statements. Blind mathematicians activated the classical network of math-related areas during mathematical reflection, similar to that found in a group of sighted professional mathematicians. Thus, brain networks for advanced mathematical reasoning can develop in the absence of visual experience. Additional activations were found in occipital cortex, even in individuals who became blind during childhood, suggesting that either mental imagery or a more radical repurposing of visual cortex may occur in blind mathematicians.

Are Supramodality and Cross-Modal Plasticity the Yin and Yang of Brain Development? From Blindness to Rehabilitation

Research in blind individuals has primarily focused for a long time on the brain plastic reorganization that occurs in early visual areas. Only more recently, scientists have developed innovative strategies to understand to what extent vision is truly a mandatory prerequisite for the brain's fine morphological architecture to develop and function. As a whole, the studies conducted to date in sighted and congenitally blind individuals have provided ample evidence that several "visual" cortical areas develop independently from visual experience and do process information content regardless of the sensory modality through which a particular stimulus is conveyed: a property named supramodality. At the same time, lack of vision leads to a structural and functional reorganization within "visual" brain areas, a phenomenon known as cross-modal plasticity. Cross-modal recruitment of the occipital cortex in visually deprived individuals represents an adaptative compensatory mechanism that mediates processing of non-visual inputs. Supramodality and cross-modal plasticity appears to be the "yin and yang" of brain development: supramodal is what takes place despite the lack of vision, whereas cross-modal is what happens because of lack of vision. Here we provide a critical overview of the research in this field and discuss the implications that these novel findings have for the development of educative/rehabilitation approaches and sensory substitution devices (SSDs) in sensory-impaired individuals.

Structural brain connectivity and cognitive ability differences: A multivariate distance matrix regression analysis

Neuroimaging research involves analyses of huge amounts of biological data that might or might not be related with cognition. This relationship is usually approached using univariate methods, and, therefore, correction methods are mandatory for reducing false positives. Nevertheless, the probability of false negatives is also increased. Multivariate frameworks have been proposed for helping to alleviate this balance. Here we apply multivariate distance matrix regression for the simultaneous analysis of biological and cognitive data, namely, structural connections among 82 brain regions and several latent factors estimating cognitive performance. We tested whether cognitive differences predict distances among individuals regarding their connectivity pattern. Beginning with 3,321 connections among regions, the 36 edges better predicted by the individuals' cognitive scores were selected. Cognitive scores were related to connectivity distances in both the full (3,321) and reduced (36) connectivity patterns. The selected edges connect regions distributed across the entire brain and the network defined by these edges supports high-order cognitive processes such as (a) (fluid) executive control, (b) (crystallized) recognition, learning, and language processing, and (c) visuospatial processing. This multivariate study suggests that one widespread, but limited number, of regions in the human brain, supports high-level cognitive ability differences. Hum Brain Mapp 38:803-816, 2017. © 2016 Wiley Periodicals, Inc.

Autism Spectrum Disorders (ASD) in Blind Children: Very High Prevalence, Potentially Better Outlook

Autism spectrum disorders affected 19 of 38 unselected children at a school for the blind in Cordoba, Argentina. Autism was linked to total congenital blindness, not blindness' etiology, acquired or incomplete blindness, sex, overt brain damage, or socioeconomic status. Autism "recovery," had occurred in 4 verbal children. Congenital blindness causes profoundly deviant sensory experience and massive reorganization of brain connectivity. Its ≥ 30 times greater prevalence than in sighted children suggests a distinct pathogenesis. Unawareness of autism's high prevalence in blind individuals includes blindness' rarity, misunderstanding of autism as "disease" rather than dimensional behavioral diagnosis, reluctance to diagnose it in blind children, and ignorance of its potentially more favorable outcome. Future investigation may suggest interventions to prevent or mitigate it.

Absence of visual experience modifies the neural basis of numerical thinking

In humans, the ability to reason about mathematical quantities depends on a frontoparietal network that includes the intraparietal sulcus (IPS). How do nature and nurture give rise to the neurobiology of numerical cognition? We asked how visual experience shapes the neural basis of numerical thinking by studying numerical cognition in congenitally blind individuals. Blind (n = 17) and blindfolded sighted (n = 19) participants solved math equations that varied in difficulty (e.g., 27 - 12 = x vs. 7 - 2 = x), and performed a control sentence comprehension task while undergoing fMRI. Whole-cortex analyses revealed that in both blind and sighted participants, the IPS and dorsolateral prefrontal cortices were more active during the math task than the language task, and activity in the IPS increased parametrically with equation difficulty. Thus, the classic frontoparietal number network is preserved in the total absence of visual experience. However, surprisingly, blind but not sighted individuals additionally recruited a subset of early visual areas during symbolic math calculation. The functional profile of these "visual" regions was identical to that of the IPS in blind but not sighted individuals. Furthermore, in blindness, number-responsive visual cortices exhibited increased functional connectivity with prefrontal and IPS regions that process numbers. We conclude that the frontoparietal number network develops independently of visual experience. In blindness, this number network colonizes parts of deafferented visual cortex. These results suggest that human cortex is highly functionally flexible early in life, and point to frontoparietal input as a mechanism of cross-modal plasticity in blindness.

Early Blindness Results in Developmental Plasticity for Auditory Motion Processing within Auditory and Occipital Cortex

Early blind subjects exhibit superior abilities for processing auditory motion, which are accompanied by enhanced BOLD responses to auditory motion within hMT+ and reduced responses within right planum temporale (rPT). Here, by comparing BOLD responses to auditory motion in hMT+ and rPT within sighted controls, early blind, late blind, and sight-recovery individuals, we were able to separately examine the effects of developmental and adult visual deprivation on cortical plasticity within these two areas. We find that both the enhanced auditory motion responses in hMT+ and the reduced functionality in rPT are driven by the absence of visual experience early in life; neither loss nor recovery of vision later in life had a discernable influence on plasticity within these areas. Cortical plasticity as a result of blindness has generally be presumed to be mediated by competition across modalities within a given cortical region. The reduced functionality within rPT as a result of early visual loss implicates an additional mechanism for cross modal plasticity as a result of early blindness—competition across different cortical areas for functional role.

The Effect of Early Visual Deprivation on the Neural Bases of Auditory Processing

Transient congenital visual deprivation affects visual and multisensory processing. In contrast, the extent to which it affects auditory processing has not been investigated systematically. Research in permanently blind individuals has revealed brain reorganization during auditory processing, involving both intramodal and crossmodal plasticity. The present study investigated the effect of transient congenital visual deprivation on the neural bases of auditory processing in humans. Cataract-reversal individuals and normally sighted controls performed a speech-in-noise task while undergoing functional magnetic resonance imaging. Although there were no behavioral group differences, groups differed in auditory cortical responses: in the normally sighted group, auditory cortex activation increased with increasing noise level, whereas in the cataract-reversal group, no activation difference was observed across noise levels. An auditory activation of visual cortex was not observed at the group level in cataract-reversal individuals. The present data suggest prevailing auditory processing advantages after transient congenital visual deprivation, even many years after sight restoration.

SIGNIFICANCE STATEMENT

The present study demonstrates that people whose sight was restored after a transient period of congenital blindness show more efficient cortical processing of auditory stimuli (here speech), similarly to what has been observed in congenitally permanently blind individuals. These results underscore the importance of early sensory experience in permanently shaping brain function.

"Visual" Cortex of Congenitally Blind Adults Responds to Syntactic Movement

Human cortex is comprised of specialized networks that support functions, such as visual motion perception and language processing. How do genes and experience contribute to this specialization? Studies of plasticity offer unique insights into this question. In congenitally blind individuals, "visual" cortex responds to auditory and tactile stimuli. Remarkably, recent evidence suggests that occipital areas participate in language processing. We asked whether in blindness, occipital cortices: (1) develop domain-specific responses to language and (2) respond to a highly specialized aspect of language-syntactic movement. Nineteen congenitally blind and 18 sighted participants took part in two fMRI experiments. We report that in congenitally blind individuals, but not in sighted controls, "visual" cortex is more active during sentence comprehension than during a sequence memory task with nonwords, or a symbolic math task. This suggests that areas of occipital cortex become selective for language, relative to other similar higher-cognitive tasks. Crucially, we find that these occipital areas respond more to sentences with syntactic movement but do not respond to the difficulty of math equations. We conclude that regions within the visual cortex of blind adults are involved in syntactic processing. Our findings suggest that the cognitive function of human cortical areas is largely determined by input during development.

SIGNIFICANCE STATEMENT

Human cortex is made up of specialized regions that perform different functions, such as visual motion perception and language processing. How do genes and experience contribute to this specialization? Studies of plasticity show that cortical areas can change function from one sensory modality to another. Here we demonstrate that input during development can alter cortical function even more dramatically. In blindness a subset of "visual" areas becomes specialized for language processing. Crucially, we find that the same "visual" areas respond to a highly specialized and uniquely human aspect of language-syntactic movement. These data suggest that human cortex has broad functional capacity during development, and input plays a major role in determining functional specialization.