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1.
Curr Opin Physiol ; 16: 50-60, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32923755

RESUMO

The human brain contains 100 billion neurons, and each neuron can have up to 200,000 connections to other neurons. Recent advancements in neuroscience-ranging from molecular studies in animal models to behavioral studies in humans-have given us deeper insights into the development of this extraordinarily intricate system. Studies show a complex interaction between biological predispositions and environment; while the gross neuroanatomy and low-level functions develop early prior to receiving environmental inputs, functional selectivity is shaped through experience, governed by the maturation of local excitatory and inhibitory circuits and synaptic plasticity during sensitive periods early in development. Plasticity does not end with the closing of the early sensitive period - the environment continues to play an important role in learning throughout the lifespan. Recent work delineating the cascade of events that initiates, controls and ends sensitive periods, offers new hope of eventually being able to remediate various clinical conditions by selectively reopening plasticity.

2.
Sci Rep ; 9(1): 9199, 2019 06 24.
Artigo em Inglês | MEDLINE | ID: mdl-31235711

RESUMO

Degenerative retinal diseases such as retinitis pigmentosa and macular degeneration cause irreversible vision loss in more than 10 million people worldwide. Retinal prostheses, now implanted in over 250 patients worldwide, electrically stimulate surviving cells in order to evoke neuronal responses that are interpreted by the brain as visual percepts ('phosphenes'). However, instead of seeing focal spots of light, current implant users perceive highly distorted phosphenes that vary in shape both across subjects and electrodes. We characterized these distortions by asking users of the Argus retinal prosthesis system (Second Sight Medical Products Inc.) to draw electrically elicited percepts on a touchscreen. Using ophthalmic fundus imaging and computational modeling, we show that elicited percepts can be accurately predicted by the topographic organization of optic nerve fiber bundles in each subject's retina, successfully replicating visual percepts ranging from 'blobs' to oriented 'streaks' and 'wedges' depending on the retinal location of the stimulating electrode. This provides the first evidence that activation of passing axon fibers accounts for the rich repertoire of phosphene shape commonly reported in psychophysical experiments, which can severely distort the quality of the generated visual experience. Overall our findings argue for more detailed modeling of biological detail across neural engineering applications.


Assuntos
Eletrodos Implantados , Degeneração Macular/cirurgia , Fosfenos , Retinite Pigmentosa/cirurgia , Próteses Visuais , Idoso , Simulação por Computador , Estimulação Elétrica , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Modelos Neurológicos , Células Ganglionares da Retina/citologia , Percepção Visual
3.
Proc Natl Acad Sci U S A ; 116(20): 10081-10086, 2019 05 14.
Artigo em Inglês | MEDLINE | ID: mdl-31036666

RESUMO

Previous studies report that human middle temporal complex (hMT+) is sensitive to auditory motion in early-blind individuals. Here, we show that hMT+ also develops selectivity for auditory frequency after early blindness, and that this selectivity is maintained after sight recovery in adulthood. Frequency selectivity was assessed using both moving band-pass and stationary pure-tone stimuli. As expected, within primary auditory cortex, both moving and stationary stimuli successfully elicited frequency-selective responses, organized in a tonotopic map, for all subjects. In early-blind and sight-recovery subjects, we saw evidence for frequency selectivity within hMT+ for the auditory stimulus that contained motion. We did not find frequency-tuned responses within hMT+ when using the stationary stimulus in either early-blind or sight-recovery subjects. We saw no evidence for auditory frequency selectivity in hMT+ in sighted subjects using either stimulus. Thus, after early blindness, hMT+ can exhibit selectivity for auditory frequency. Remarkably, this auditory frequency tuning persists in two adult sight-recovery subjects, showing that, in these subjects, auditory frequency-tuned responses can coexist with visually driven responses in hMT+.


Assuntos
Córtex Auditivo/fisiologia , Percepção Auditiva/fisiologia , Cegueira/fisiopatologia , Percepção de Movimento/fisiologia , Lobo Occipital/fisiologia , Adulto , Córtex Auditivo/diagnóstico por imagem , Estudos de Casos e Controles , Feminino , Humanos , Imagem por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Lobo Occipital/diagnóstico por imagem
4.
J Neurosci ; 39(26): 5143-5152, 2019 06 26.
Artigo em Inglês | MEDLINE | ID: mdl-31010853

RESUMO

Early loss of vision is classically linked to large-scale cross-modal plasticity within occipital cortex. Much less is known about the effects of early blindness on auditory cortex. Here, we examine the effects of early blindness on the cortical representation of auditory frequency within human primary and secondary auditory areas using fMRI. We observe that 4 individuals with early blindness (2 females), and a group of 5 individuals with anophthalmia (1 female), a condition in which both eyes fail to develop, have lower response amplitudes and narrower voxelwise tuning bandwidths compared with a group of typically sighted individuals. These results provide some of the first evidence in human participants for compensatory plasticity within nondeprived sensory areas as a result of sensory loss.SIGNIFICANCE STATEMENT Early blindness has been linked to enhanced perception of the auditory world, including auditory localization and pitch perception. Here we used fMRI to compare neural responses with auditory stimuli within auditory cortex across sighted, early blind, and anophthalmic individuals, in whom both eyes fail to develop. We find more refined frequency tuning in blind subjects, providing some of the first evidence in human subjects for compensation within nondeprived primary sensory areas as a result of blindness early in life.


Assuntos
Anoftalmia/diagnóstico por imagem , Córtex Auditivo/diagnóstico por imagem , Percepção Auditiva/fisiologia , Cegueira/diagnóstico por imagem , Plasticidade Neuronal/fisiologia , Estimulação Acústica , Adulto , Anoftalmia/fisiopatologia , Córtex Auditivo/fisiopatologia , Cegueira/fisiopatologia , Feminino , Neuroimagem Funcional , Humanos , Imagem por Ressonância Magnética , Masculino , Pessoa de Meia-Idade
5.
Cereb Cortex ; 29(10): 4321-4333, 2019 09 13.
Artigo em Inglês | MEDLINE | ID: mdl-30561529

RESUMO

Blindness early in life induces permanent alterations in brain anatomy, including reduced surface area of primary visual cortex (V1). Bilateral enucleation early in development causes greater reductions in primary visual cortex surface area than at later times. However, the time at which cortical surface area expansion is no longer sensitive to enucleation is not clearly established, despite being an important milestone for cortical development. Using histological and MRI techniques, we investigated how reductions in the surface area of V1 depends on the timing of blindness onset in rats, ferrets and humans. To compare data across species, we translated ages of all species to a common neuro-developmental event-time (ET) scale. Consistently, blindness during early cortical expansion induced large (~40%) reductions in V1 surface area, in rats and ferrets, while blindness occurring later had diminishing effects. Longitudinal measurements on ferrets confirmed that early enucleation disrupted cortical expansion, rather than inducing enhanced pruning. We modeled the ET associated with the conclusion of the effect of blindness on surface area at maturity (ETc), relative to the normal conclusion of visual cortex surface area expansion, (ETdev). A final analysis combining our data with extant published data confirmed that ETc occurred well before ETdev.


Assuntos
Cegueira/patologia , Cegueira/fisiopatologia , Furões/anatomia & histologia , Furões/crescimento & desenvolvimento , Privação Sensorial/fisiologia , Córtex Visual/crescimento & desenvolvimento , Córtex Visual/patologia , Idade de Início , Animais , Córtex Cerebral/crescimento & desenvolvimento , Córtex Cerebral/patologia , Humanos , Ratos , Especificidade da Espécie
6.
Annu Rev Vis Sci ; 4: 337-356, 2018 09 15.
Artigo em Inglês | MEDLINE | ID: mdl-29975591

RESUMO

Early blindness causes fundamental alterations of neural function across more than 25% of cortex-changes that span the gamut from metabolism to behavior and collectively represent one of the most dramatic examples of plasticity in the human brain. The goal of this review is to describe how the remarkable behavioral and neuroanatomical compensations demonstrated by blind individuals provide insights into the extent, mechanisms, and limits of human brain plasticity.


Assuntos
Cegueira/fisiopatologia , Córtex Cerebral/fisiologia , Plasticidade Neuronal/fisiologia , Privação Sensorial/fisiologia , Retroalimentação Sensorial/fisiologia , Humanos
8.
Nature ; 555(7695): 165, 2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-32095010
9.
Front Psychol ; 8: 1983, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-29184522

RESUMO

Here we show that, using functional magnetic resonance imaging (fMRI) blood-oxygen level dependent (BOLD) responses in human primary auditory cortex, it is possible to reconstruct the sequence of tones that a person has been listening to over time. First, we characterized the tonotopic organization of each subject's auditory cortex by measuring auditory responses to randomized pure tone stimuli and modeling the frequency tuning of each fMRI voxel as a Gaussian in log frequency space. Then, we tested our model by examining its ability to work in reverse. Auditory responses were re-collected in the same subjects, except this time they listened to sequences of frequencies taken from simple songs (e.g., "Somewhere Over the Rainbow"). By finding the frequency that minimized the difference between the model's prediction of BOLD responses and actual BOLD responses, we were able to reconstruct tone sequences, with mean frequency estimation errors of half an octave or less, and little evidence of systematic biases.

10.
J Neural Eng ; 14(5): 051003, 2017 10.
Artigo em Inglês | MEDLINE | ID: mdl-28612755

RESUMO

The 'bionic eye'-so long a dream of the future-is finally becoming a reality with retinal prostheses available to patients in both the US and Europe. However, clinical experience with these implants has made it apparent that the visual information provided by these devices differs substantially from normal sight. Consequently, the ability of patients to learn to make use of this abnormal retinal input plays a critical role in whether or not some functional vision is successfully regained. The goal of the present review is to summarize the vast basic science literature on developmental and adult cortical plasticity with an emphasis on how this literature might relate to the field of prosthetic vision. We begin with describing the distortion and information loss likely to be experienced by visual prosthesis users. We then define cortical plasticity and perceptual learning, and describe what is known, and what is unknown, about visual plasticity across the hierarchy of brain regions involved in visual processing, and across different stages of life. We close by discussing what is known about brain plasticity in sight restoration patients and discuss biological mechanisms that might eventually be harnessed to improve visual learning in these patients.


Assuntos
Aprendizagem/fisiologia , Plasticidade Neuronal/fisiologia , Optogenética/métodos , Córtex Visual/fisiologia , Percepção Visual/fisiologia , Próteses Visuais , Humanos , Optogenética/tendências , Próteses Visuais/tendências
11.
J Vis ; 17(2): 4, 2017 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-28196374

RESUMO

Visual neuroscience has traditionally focused much of its attention on understanding the response properties of single neurons or neuronal ensembles. The visual white matter and the long-range neuronal connections it supports are fundamental in establishing such neuronal response properties and visual function. This review article provides an introduction to measurements and methods to study the human visual white matter using diffusion MRI. These methods allow us to measure the microstructural and macrostructural properties of the white matter in living human individuals; they allow us to trace long-range connections between neurons in different parts of the visual system and to measure the biophysical properties of these connections. We also review a range of findings from recent studies on connections between different visual field maps, the effects of visual impairment on the white matter, and the properties underlying networks that process visual information supporting visual face recognition. Finally, we discuss a few promising directions for future studies. These include new methods for analysis of MRI data, open datasets that are becoming available to study brain connectivity and white matter properties, and open source software for the analysis of these data.


Assuntos
Imagem de Difusão por Ressonância Magnética/métodos , Fibras Nervosas/fisiologia , Neurônios/fisiologia , Vias Visuais/fisiologia , Substância Branca/diagnóstico por imagem , Mapeamento Encefálico/métodos , Humanos , Transtornos da Visão/fisiopatologia , Campos Visuais/fisiologia
12.
Front Hum Neurosci ; 10: 324, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27458357

RESUMO

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.

13.
J Neurosci ; 35(36): 12366-82, 2015 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-26354906

RESUMO

Early visual areas have neuronal receptive fields that form a sampling mosaic of visual space, resulting in a series of retinotopic maps in which the same region of space is represented in multiple visual areas. It is not clear to what extent the development and maintenance of this retinotopic organization in humans depend on retinal waves and/or visual experience. We examined the corticocortical receptive field organization of resting-state BOLD data in normally sighted, early blind, and anophthalmic (in which both eyes fail to develop) individuals and found that resting-state correlations between V1 and V2/V3 were retinotopically organized for all subject groups. These results show that the gross retinotopic pattern of resting-state connectivity across V1-V3 requires neither retinal waves nor visual experience to develop and persist into adulthood. Significance statement: Evidence from resting-state BOLD data suggests that the connections between early visual areas develop and are maintained even in the absence of retinal waves and visual experience.


Assuntos
Anoftalmia/fisiopatologia , Cegueira/fisiopatologia , Córtex Cerebral/fisiologia , Potenciais da Membrana , Percepção Visual , Adulto , Mapeamento Encefálico , Estudos de Casos e Controles , Córtex Cerebral/fisiopatologia , Potenciais Evocados Visuais , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Retina/fisiologia , Retina/fisiopatologia , Campos Visuais
14.
Philos Trans R Soc Lond B Biol Sci ; 370(1677): 20140208, 2015 Sep 19.
Artigo em Inglês | MEDLINE | ID: mdl-26240423

RESUMO

An extraordinary variety of sight recovery therapies are either about to begin clinical trials, have begun clinical trials, or are currently being implanted in patients. However, as yet we have little insight into the perceptual experience likely to be produced by these implants. This review focuses on methodologies, such as optogenetics, small molecule photoswitches and electrical prostheses, which use artificial stimulation of the retina to elicit percepts. For each of these technologies, the interplay between the stimulating technology and the underlying neurophysiology is likely to result in distortions of the perceptual experience. Here, we describe some of these potential distortions and discuss how they might be minimized either through changes in the encoding model or through cortical plasticity.


Assuntos
Transtornos da Visão/terapia , Percepção Visual/fisiologia , Terapia por Estimulação Elétrica/métodos , Humanos , Modelos Biológicos , Optogenética/métodos , Retina/citologia , Retina/fisiologia , Transtornos da Visão/fisiopatologia , Transtornos da Visão/psicologia , Próteses Visuais
15.
J Neurophysiol ; 114(3): 1725-33, 2015 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-26180125

RESUMO

Congenital blindness leads to large-scale functional and structural reorganization in the occipital cortex, but relatively little is known about the neurochemical changes underlying this cross-modal plasticity. To investigate the effect of complete and early visual deafferentation on the concentration of metabolites in the pericalcarine cortex, (1)H magnetic resonance spectroscopy was performed in 14 sighted subjects and 5 subjects with bilateral anophthalmia, a condition in which both eyes fail to develop. In the pericalcarine cortex, where primary visual cortex is normally located, the proportion of gray matter was significantly greater, and levels of choline, glutamate, glutamine, myo-inositol, and total creatine were elevated in anophthalmic relative to sighted subjects. Anophthalmia had no effect on the structure or neurochemistry of a sensorimotor cortex control region. More gray matter, combined with high levels of choline and myo-inositol, resembles the profile of the cortex at birth and suggests that the lack of visual input from the eyes might have delayed or arrested the maturation of this cortical region. High levels of choline and glutamate/glutamine are consistent with enhanced excitatory circuits in the anophthalmic occipital cortex, which could reflect a shift toward enhanced plasticity or sensitivity that could in turn mediate or unmask cross-modal responses. Finally, it is possible that the change in function of the occipital cortex results in biochemical profiles that resemble those of auditory, language, or somatosensory cortex.


Assuntos
Anoftalmia/metabolismo , Córtex Visual/metabolismo , Adulto , Estudos de Casos e Controles , Colina/metabolismo , Creatina/metabolismo , Feminino , Ácido Glutâmico/metabolismo , Glutamina/metabolismo , Humanos , Inositol/metabolismo , Masculino , Córtex Somatossensorial/metabolismo
16.
Neuroimage ; 119: 187-96, 2015 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-26123373

RESUMO

Here, we examine overlap between tactile and visual motion BOLD responses within the human MT+ complex. Although several studies have reported tactile responses overlapping with hMT+, many used group average analyses, leaving it unclear whether these responses were restricted to subregions of hMT+. Moreover, previous studies either employed a tactile task or passive stimulation, leaving it unclear whether or not tactile responses in hMT+ are simply the consequence of visual imagery. Here, we carried out a replication of one of the classic papers finding tactile responses in hMT+. We mapped MT and MST in individual subjects using visual field localizers. We then examined responses to tactile motion on the arm, either presented passively or in the presence of a visual task performed at fixation designed to minimize visualization of the concurrent tactile stimulation. To our surprise, without a visual task, we found only weak tactile motion responses in MT (6% of voxels showing tactile responses) and MST (2% of voxels). With an unrelated visual task designed to withdraw attention from the tactile modality, responses in MST were reduced to almost nothing (<1% regions). Consistent with previous results, we did observe tactile responses in STS regions superior and anterior to hMT+. Despite the lack of individual overlap, group-averaged responses produced strong spurious overlap between tactile and visual motion responses within hMT+ that resembled those observed in previous studies. The weak nature of tactile responses in hMT+ (and their abolition by withdrawal of attention) suggests that hMT+ may not serve as a supramodal motion processing module.


Assuntos
Percepção de Movimento/fisiologia , Lobo Temporal/fisiologia , Percepção do Tato/fisiologia , Adulto , Mapeamento Encefálico , Feminino , Humanos , Imagem por Ressonância Magnética , Masculino , Estimulação Luminosa , Estimulação Física , Adulto Jovem
18.
Psychol Sci ; 26(4): 393-401, 2015 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-25740284

RESUMO

In 2000, monocular vision was restored to M. M., who had been blind between the ages of 3 and 46 years. Tests carried out over 2 years following the surgery revealed impairments of 3-D form, object, and face processing and an absence of object- and face-selective blood-oxygen-level-dependent responses in ventral visual cortex. In the present research, we reexamined M. M. to test for experience-dependent recovery of visual function. Behaviorally, M. M. remains impaired in 3-D form, object, and face processing. Accordingly, we found little to no evidence of the category-selective organization within ventral visual cortex typically associated with face, body, scene, or object processing. We did observe remarkably normal object selectivity within lateral occipital cortex, consistent with M. M.'s previously reported shape-discrimination performance. Together, these findings provide little evidence for recovery of high-level visual function after more than a decade of visual experience in adulthood.


Assuntos
Cegueira/fisiopatologia , Plasticidade Neuronal/fisiologia , Visão Monocular/fisiologia , Córtex Visual/fisiopatologia , Adulto , Cegueira/terapia , Humanos , Masculino , Pessoa de Meia-Idade , Reconhecimento Visual de Modelos/fisiologia
19.
J Neurophysiol ; 113(7): 2889-99, 2015 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-25673746

RESUMO

Lack of visual input early in life results in occipital cortical responses to auditory and tactile stimuli. However, it remains unclear whether cross-modal plasticity also occurs in subcortical pathways. With the use of functional magnetic resonance imaging, auditory responses were compared across individuals with congenital anophthalmia (absence of eyes), those with early onset (in the first few years of life) blindness, and normally sighted individuals. We find that the superior colliculus, a "visual" subcortical structure, is recruited by the auditory system in congenital and early onset blindness. Additionally, auditory subcortical responses to monaural stimuli were altered as a result of blindness. Specifically, responses in the auditory thalamus were equally strong to contralateral and ipsilateral stimulation in both groups of blind subjects, whereas sighted controls showed stronger responses to contralateral stimulation. These findings suggest that early blindness results in substantial reorganization of subcortical auditory responses.


Assuntos
Vias Auditivas/fisiopatologia , Percepção Auditiva , Cegueira/fisiopatologia , Encéfalo/fisiopatologia , Rede Nervosa/fisiopatologia , Plasticidade Neuronal , Adulto , Período Crítico Psicológico , Feminino , Humanos , Masculino , Adulto Jovem
20.
Neuroimage ; 105: 428-39, 2015 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-25449742

RESUMO

Here we describe a method for measuring tonotopic maps and estimating bandwidth for voxels in human primary auditory cortex (PAC) using a modification of the population Receptive Field (pRF) model, developed for retinotopic mapping in visual cortex by Dumoulin and Wandell (2008). The pRF method reliably estimates tonotopic maps in the presence of acoustic scanner noise, and has two advantages over phase-encoding techniques. First, the stimulus design is flexible and need not be a frequency progression, thereby reducing biases due to habituation, expectation, and estimation artifacts, as well as reducing the effects of spatio-temporal BOLD nonlinearities. Second, the pRF method can provide estimates of bandwidth as a function of frequency. We find that bandwidth estimates are narrower for voxels within the PAC than in surrounding auditory responsive regions (non-PAC).


Assuntos
Córtex Auditivo/fisiologia , Percepção Auditiva/fisiologia , Mapeamento Encefálico/métodos , Adulto , Feminino , Humanos , Imagem por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Adulto Jovem
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