Brain Plasticity in Blind Subjects Centralizes Beyond the Modal Cortices

Reorganization of integration and segregation networks in brain-based visual impairment

Growing evidence suggests that cerebral connectivity changes its network organization by altering modular topology in response to developmental and environmental experience. However, changes in cerebral connectivity associated with visual impairment due to early neurological injury are still not fully understood. Cerebral visual impairment (CVI) is a brain-based visual disorder associated with damage and maldevelopment of retrochiasmal pathways and areas implicated in visual processing. In this study, we used a multimodal imaging approach and connectomic analyses based on structural (voxel-based morphometry; VBM) and resting state functional connectivity (rsfc) to investigate differences in weighted degree and link-level connectivity in individuals with CVI compared to controls with neurotypical development. We found that participants with CVI showed significantly reduced grey matter volume within the primary visual cortex and intraparietal sulcus (IPS) compared to controls. Participants with CVI also exhibited marked reorganization characterized by increased integration of visual connectivity to somatosensory and multimodal integration areas (dorsal and ventral attention regions) and lower connectivity from visual to limbic and default mode networks. Link-level functional changes in CVI were also associated with key clinical outcomes related to visual function and development. These findings provide early insight into how visual impairment related to early brain injury distinctly reorganizes the functional network architecture of the human brain.

Early attentional processing and cortical remapping strategies of tactile stimuli in adults with an early and late-onset visual impairment: A cross-sectional study

Neuroplastic changes appear in people with visual impairment (VI) and they show greater tactile abilities. Improvements in performance could be associated with the development of enhanced early attentional processes based on neuroplasticity. Currently, the various early attentional and cortical remapping strategies that are utilized by people with early (EB) and late-onset blindness (LB) remain unclear. Thus, more research is required to develop effective rehabilitation programs and substitution devices. Our objective was to explore the differences in spatial tactile brain processing in adults with EB, LB and a sighted control group (CG). In this cross-sectional study 27 participants with VI were categorized into EB (n = 14) and LB (n = 13) groups. They were then compared with a CG (n = 15). A vibrotactile device and event-related potentials (ERPs) were utilized while participants performed a spatial tactile line recognition task. The P100 latency and cortical areas of maximal activity were analyzed during the task. The three groups had no statistical differences in P100 latency (p>0.05). All subjects showed significant activation in the right superior frontal areas. Only individuals with VI activated the left superior frontal regions. In EB subjects, a higher activation was found in the mid-frontal and occipital areas. A higher activation of the mid-frontal, anterior cingulate cortex and orbitofrontal zones was observed in LB participants. Compared to the CG, LB individuals showed greater activity in the left orbitofrontal zone, while EB exhibited greater activity in the right superior parietal cortex. The EB had greater activity in the left orbitofrontal region compared to the LB. People with VI may not have faster early attentional processing. EB subjects activate the occipital lobe and right superior parietal cortex during tactile stimulation because of an early lack of visual stimuli and a multimodal information processing. In individuals with LB and EB the orbitofrontal area is activated, suggesting greater emotional processing.

Nonverbal hand movements serve self-related functions in blind individuals

OBJECTIVE

Blind individuals suffer from visual (i.e., sensory) deprivation. So-called "blindisms" (or "nervous" movements) have been described as the nonverbal consequence of such deprivation. However, the neuropsychological functions of such behaviours of blind individuals have not been investigated yet. We therefore analyzed the nonverbal hand movement and gestural behaviour of blind individuals with the hypothesis that their nonverbal expressions rather serve their own mental state than the nonverbal (/gestural) depiction of (mental) images.

METHODS

The (entire) nonverbal hand movement and gestural behaviour of right-handed healthy blind, (matched) sighted, and (matched) sighted/blindfolded individuals was analyzed during a standardized interview situation (about emotions and actions) by four independent (certified) raters employing the Neuropsychological Gesture (NEUROGES) Coding System.

RESULTS

The results show no difference of the overall hand movement activity between blind, sighted, and sighted/blindfolded individuals. Increased position shifts and on body focused hand movements were found in blind individuals when compared to sighted and sighted/blindfolded individuals. Sighted but neither blind nor sighted/blindfolded individuals increase egocentric deictic and pantomime gestures during the re-narration of an audio story.

DISCUSSION

Blind individuals seem to desynchronize during conversation (shifts), increase self-stimulation behaviour due to sensory deprivation (on body), but reduce the nonverbal transfer of mental images via hand gestures. We therefore conclude that nonverbal hand movements of blind individuals rather serve their own mental state but not for the transfer of mental images.

The Parietal Lobe in Alzheimer’s Disease and Blindness

The progressive aging of the population will notably increase the burden of those diseases which leads to a disabling situation, such as Alzheimer’s disease (AD) and ophthalmological diseases that cause a visual impairment (VI). Eye diseases that cause a VI raise neuroplastic processes in the parietal lobe. Meanwhile, the aforementioned lobe suffers a severe decline throughout AD. From this perspective, diving deeper into the particularities of the parietal lobe is of paramount importance. In this article, we discuss the functions of the parietal lobe, review the parietal anatomical and pathophysiological peculiarities in AD, and also describe some of the changes in the parietal region that occur after VI. Although the alterations in the hippocampus and the temporal lobe have been well documented in AD, the alterations of the parietal lobe have been less thoroughly explored. Recent neuroimaging studies have revealed that some metabolic and perfusion impairments along with a reduction of the white and grey matter could take place in the parietal lobe during AD. Conversely, it has been speculated that blinding ocular diseases induce a remodeling of the parietal region which is observable through the improvement of the integration of multimodal stimuli and in the increase of the volume of this cortical region. Based on current findings concerning the parietal lobe in both pathologies, we hypothesize that the increased activity of the parietal lobe in people with VI may diminish the neurodegeneration of this brain region in those who are visually impaired by oculardiseases.

Analysing the Influence of Selected Eye Dysfunctions on Palpation Abilities of Massage Therapists

Introduction: Palpation arises controversy in the field of physiotherapy. On the one hand, this method provides a lot of valuable information. On the other, issues related to its reliability still exist. Additionally, questions about factors affecting palpation and users’ dispositions should be taken into consideration. Research objectives: The main aim of the study was to determine the impact of visual impairment on the palpatory skills of massage therapists. Material and methods: The research involved 58 participants divided into 3 groups. The first group consisted of 23, visually-impaired massage therapists, the second one was made up of 22 massage therapists and the control group consisted of 13 people unrelated to massage. The subjects took the hair test, the weight test and the measurement of Static Two-Point Discrimination within the fingertips I-III, thenar and hypothenar. Results: The analysis does not show any significant differences between the first and second group. Statistics reveal differences between the group of massage practitioners (group 1 and 2) and the control group. Visual impairment was not the most influential factor in the study. Conclusions: The level of palpation skills may be modified in both visually-impaired and healthy people. However, mechanisms that allow these modifications remain unclear. On the basis of the research, visual impairment is not considered as the only factor affecting palpation skills. Experience in palpation may well be an equally important factor.

Beat Detection Recruits the Visual Cortex in Early Blind Subjects

Using functional magnetic resonance imaging, here we monitored the brain activity in 12 early blind subjects and 12 blindfolded control subjects, matched for age, gender and musical experience, during a beat detection task. Subjects were required to discriminate regular ("beat") from irregular ("no beat") rhythmic sequences composed of sounds or vibrotactile stimulations. In both sensory modalities, the brain activity differences between the two groups involved heteromodal brain regions including parietal and frontal cortical areas and occipital brain areas, that were recruited in the early blind group only. Accordingly, early blindness induced brain plasticity changes in the cerebral pathways involved in rhythm perception, with a participation of the visually deprived occipital brain areas whatever the sensory modality for input. We conclude that the visually deprived cortex switches its input modality from vision to audition and vibrotactile sense to perform this temporal processing task, supporting the concept of a metamodal, multisensory organization of this cortex.

Data-Driven Classification of Spectral Profiles Reveals Brain Region-Specific Plasticity in Blindness

Congenital blindness has been shown to result in behavioral adaptation and neuronal reorganization, but the underlying neuronal mechanisms are largely unknown. Brain rhythms are characteristic for anatomically defined brain regions and provide a putative mechanistic link to cognitive processes. In a novel approach, using magnetoencephalography resting state data of congenitally blind and sighted humans, deprivation-related changes in spectral profiles were mapped to the cortex using clustering and classification procedures. Altered spectral profiles in visual areas suggest changes in visual alpha-gamma band inhibitory-excitatory circuits. Remarkably, spectral profiles were also altered in auditory and right frontal areas showing increased power in theta-to-beta frequency bands in blind compared with sighted individuals, possibly related to adaptive auditory and higher cognitive processing. Moreover, occipital alpha correlated with microstructural white matter properties extending bilaterally across posterior parts of the brain. We provide evidence that visual deprivation selectively modulates spectral profiles, possibly reflecting structural and functional adaptation.

Brain Entropy During Aging Through a Free Energy Principle Approach

Neural complexity and brain entropy (BEN) have gained greater interest in recent years. The dynamics of neural signals and their relations with information processing continue to be investigated through different measures in a variety of noteworthy studies. The BEN of spontaneous neural activity decreases during states of reduced consciousness. This evidence has been showed in primary consciousness states, such as psychedelic states, under the name of "the entropic brain hypothesis." In this manuscript we propose an extension of this hypothesis to physiological and pathological aging. We review this particular facet of the complexity of the brain, mentioning studies that have investigated BEN in primary consciousness states, and extending this view to the field of neuroaging with a focus on resting-state functional Magnetic Resonance Imaging. We first introduce historic and conceptual ideas about entropy and neural complexity, treating the mindbrain as a complex nonlinear dynamic adaptive system, in light of the free energy principle. Then, we review the studies in this field, analyzing the idea that the aim of the neurocognitive system is to maintain a dynamic state of balance between order and chaos, both in terms of dynamics of neural signals and functional connectivity. In our exploration we will review studies both on acute psychedelic states and more chronic psychotic states and traits, such as those in schizophrenia, in order to show the increase of entropy in those states. Then we extend our exploration to physiological and pathological aging, where BEN is reduced. Finally, we propose an interpretation of these results, defining a general trend of BEN in primary states and cognitive aging.

Multisensory inclusive design with sensory substitution

Sensory substitution techniques are perceptual and cognitive phenomena used to represent one sensory form with an alternative. Current applications of sensory substitution techniques are typically focused on the development of assistive technologies whereby visually impaired users can acquire visual information via auditory and tactile cross-modal feedback. But despite their evident success in scientific research and furthering theory development in cognition, sensory substitution techniques have not yet gained widespread adoption within sensory-impaired populations. Here we argue that shifting the focus from assistive to mainstream applications may resolve some of the current issues regarding the use of sensory substitution devices to improve outcomes for those with disabilities. This article provides a tutorial guide on how to use research into multisensory processing and sensory substitution techniques from the cognitive sciences to design new inclusive cross-modal displays. A greater focus on developing inclusive mainstream applications could lead to innovative technologies that could be enjoyed by every person.

Posterior parietal cortex contributions to cross-modal brain plasticity upon sensory loss

Sensory loss causes compensatory behavior, like echolocation upon vision loss or improved visual motion detection upon deafness. This is enabled by recruitment of the deprived cortical area by the intact senses. Such cross-modal plasticity can however hamper rehabilitation via sensory substitution devices. To steer rehabilitation towards the desired outcome for the patient, having control over the cross-modal take-over is essential. Evidence accumulates to support a role for the posterior parietal cortex (PPC) in multimodal plasticity. This area shows increased activity after sensory loss, keeping similar functions but driven by other senses. Patient-specific factors like stress, social situation, age and attention, have a significant influence on the PPC and on cross-modal plasticity. We propose that understanding the response of the PPC to sensory loss and context is extremely important for determining the best possible implant-based therapies, and that mouse research holds potential to help unraveling the underlying anatomical, cellular and neuromodulatory mechanisms.

Neuroplasticity and Braille reading

This article brings review of the studies and their findings about neuroplasticity of the brain and Braille reading, as well as some connections between the two. The goal of the article is to combine knowledge from different disciplines, thus enabling development of new efficient programs in rehabilitation. A lot of research has shown the possibility of brain reorganization (plasticity), indicating the creation of new neuron connections in people with vision loss which relate to Braille reading, especially in late-onset vision loss.

Organization of the commissural fiber system in congenital and late-onset blindness

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Larger anterior commissure (AC) in congenitally (CB) and late blind (LB) subjects.

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Decreased fractional anisotropy (FA) of the posterior part of AC (pAC) in CB and LB.

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Decreased FA in pAC is paralleled by increased number of pAC streamlines in CB only.

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Selective reduction of the splenium of the corpus callosum (CC) in CB and LB.

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Reduction of splenium correlated with decrease in streamlines and tract volume.

We investigated the effects of blindness on the structural and functional integrity of the corpus callosum and the anterior commissure (AC), which together form the two major components of the commissural pathways. Twelve congenitally blind (CB), 15 late blind (LB; mean onset of blindness of 16.6 ± 8.9 years), and 15 matched normally sighted controls (SC) participated in a multimodal brain imaging study. Magnetic resonance imaging(MRI) data were acquired using a 3T scanner, and included a structural brain scan, resting state functional MRI, and diffusion-weighted imaging. We used tractography to divide the AC into its anterior (aAC) and posterior (pAC) branch. Virtual tract dissection was performed using a deterministic spherical deconvolution tractography algorithm. The corpus callosum was subdivided into five subregions based on the criteria described by Witelson and modified by Bermudez and Zatorre. Our data revealed decreased fractional anisotropy of the pAC in CB and LB compared to SC, together with an increase in the number of streamlines in CB only. In addition, the AC surface area was significantly larger in CB compared to SC and LB, and correlated with the number of streamlines in pAC (rho = 0.55) and tract volume (rho = 0.46). As for the corpus callosum, the splenial part was significantly smaller in CB and LB, and fewer streamlines passed through it. We did not find group differences in functional connectivity of cortical areas connected by fibers crossing any of the five callosal subregions. The present data suggest that the two main components of the commissural system undergo neuroplastic changes, irrespective of the age of onset of blindness, although the alterations observed in the AC are more important in congenital than late-onset blindness.

Neuroplasticity in visual impairments

The visual acuity loss enables the brain to access new pathways in the quest to overcome the visual limitation and this is wellknown as neuroplasticity which have mechanisms to cortical reorganization. In this review, we related the evidences about the neuroplasticity as well as cortical anatomical differences and functional repercussions in visual impairments. We performed a systematic review of PUBMED database, without date or status publication restrictions. The findings demonstrate that the visual impairment produce a compensatory sensorial effect, in which non-visual areas are related to both cross (visual congenital) and multimodal (late blind) neuroplasticity.

Balance in Blind Subjects: Cane and Fingertip Touch Induce Similar Extent and Promptness of Stance Stabilization

Subjects with low vision often use a cane when standing and walking autonomously in everyday life. One aim of this study was to assess differences in the body stabilizing effect produced by the contact of the cane with the ground or by the fingertip touch of a firm surface. Another aim was to estimate the promptness of balance stabilization (or destabilization) on adding (or withdrawing) the haptic input from cane or fingertip. Twelve blind subjects and two subjects with severe visual impairment participated in two experimental protocols while maintaining the tandem Romberg posture on a force platform. In one protocol, subjects lowered the cane to a second platform on the ground and lifted it in sequence at their own pace. In the other protocol, they touched an instrumented pad with the index finger and withdrew the finger from the pad in sequence. In both protocols, subjects were asked to exert a force not granting mechanical stabilization. Under steady-state condition, the finger touch or the contact of the cane with the ground significantly reduced (to ∼78% and ∼86%, respectively) the amplitude of medio-lateral oscillation of the centre of foot pressure (CoP). Oscillation then increased when haptic information was removed. The delay to the change in body oscillation after the haptic shift was longer for addition than withdrawal of the haptic information (∼1.4 s and ∼0.7 s, respectively; p < 0.001), but was not different between the two haptic conditions (finger and cane). Similar stabilizing effects of input from cane on the ground and from fingertip touch, and similar latencies to integrate haptic cue from both sources, suggest that the process of integration of the input for balance control is initiated by the haptic stimulus at the interface cane-hand. Use of a tool is as helpful as the fingertip input, and does not produce different stabilization. Further, the latencies to haptic cue integration (from fingertip or cane) are similar to those previously found in a group of sighted subjects, suggesting that integration delays for automatic balance stabilization are not modified by visual impairment. Haptic input from a tool is easily exploited by the neural circuits subserving automatic balance stabilization in blind people, and its use should be enforced by sensory-enhancing devices and appropriate training.

A novel paradigm to study spatial memory skills in blind individuals through the auditory modality

Spatial memory is a multimodal representation of the environment, which can be mediated by different sensory signals. Here we investigate how the auditory modality influences memorization, contributing to the mental representation of a scene. We designed an audio test inspired by a validated spatial memory test, the Corsi-Block test for blind individuals. The test was carried out in two different conditions, with non-semantic and semantic stimuli, presented in different sessions and displaced on an audio-tactile device. Furthermore, the semantic sounds were spatially displaced in order to reproduce an audio scene, explored by participants during the test. Thus, we verified if semantic rather than non-semantic sounds are better recalled and whether exposure to an auditory scene can enhance memorization skills. Our results show that sighted subjects performed better than blind participants after the exploration of the semantic scene. This suggests that blind participants focus on the perceived sound positions and do not use items’ locations learned during the exploration. We discuss these results in terms of the role of visual experience on spatial memorization skills and the ability to take advantage of semantic information stored in the memory.

Superior non-specific motor learning in the blind

It is well established that blindness induces changes in cerebral function and structure, namely affecting the somatomotor regions. However, the behavioural significance of these changes on the motor system, and on motor learning in particular, remains elusive. In this study, we used a modified version of the serial reaction time task (SRTT) with auditory cues to assess sequence specific and non-specific motor learning in blind adults and sighted controls, and compare them with sighted controls performing the classic visual SRTT. Our results show that the auditory SRTT faithfully replicates the typical learning pattern obtained with the visual SRTT. On the auditory SRTT, blind individuals consistently showed faster reaction times than sighted controls, being at par with sighted individuals performing the visual SRTT. On the other hand, blind participants displayed a particular pattern of motor learning in comparison to both sighted groups; while controls improved prominently on sequence specific learning, blind individuals displayed comparable performance on both specific and non-specific learning, markedly outperforming the control groups on non-specific learning. These results show that blindness, in addition to causing long-term changes in cortical organisation, can also influence dynamic neuroplastic mechanisms in systems beyond those typically associated with compensatory sensory processing.

Brain circuit-gene expression relationships and neuroplasticity of multisensory cortices in blind children

Sensory deprivation reorganizes neurocircuits in the human brain. The biological basis of such neuroplastic adaptations remains elusive. In this study, we applied two complementary graph theory-based functional connectivity analyses, one to evaluate whole-brain functional connectivity relationships and the second to specifically delineate distributed network connectivity profiles downstream of primary sensory cortices, to investigate neural reorganization in blind children compared with sighted controls. We also examined the relationship between connectivity changes and neuroplasticity-related gene expression profiles in the cerebral cortex. We observed that multisensory integration areas exhibited enhanced functional connectivity in blind children and that this reorganization was spatially associated with the transcription levels of specific members of the cAMP Response Element Binding protein gene family. Using systems-level analyses, this study advances our understanding of human neuroplasticity and its genetic underpinnings following sensory deprivation.