Sensory cortical organization and cross-modal plasticity in blind subjects

描述(申请人提供)：视觉剥夺是最极端的情况之一，导致大脑区域采用新的功能来应对环境限制，即补偿感觉通道的丧失。在视觉剥夺动物和盲人身上的研究早就证明了视觉皮质处理非视觉信息的跨模式招募。然而，关于重组的枕叶皮质的功能划分以及它在处理非视觉信息和高级认知功能中的确切作用，人们知之甚少。本项目的主要目的是(1)确定盲人枕叶皮质的感觉组织，(2)确定盲人枕叶皮质非视觉输入的来源，以及(3)确定盲人枕叶皮质在处理非视觉刺激过程中的功能作用，特别是在使用感觉替代装置时。使用功能磁共振成像(FMRI)，我们将检查与触觉和听觉刺激相关的大脑活动，同时受试者试图识别或定位刺激。这将使我们能够确定重组的枕叶皮质中是否存在区域特异性，用于感觉通道和/或识别和定位。利用扩散张量成像(DTI)和基于体素的形态计量学(VBM)这两种较新的结构磁共振成像技术，我们将研究盲人大脑适应性变化的结构基础。VBM将允许我们检查盲人枕叶皮质中的灰质细胞密度和体积是否与视力正常的人的枕叶皮质中的相同；DTI将检查两组受试者中投射到枕叶皮质和从枕叶皮质投射的白质纤维束的强度，从而确定盲人非视觉输入来源的相对变化。为了测试失明在多大程度上伴随着非视觉能力的增强，并确定在盲人中枕叶皮质的功能作用，我们将补充大脑成像和扩展的心理物理评估。我们将检验行为表现与通过触觉或听觉刺激激活大脑区域的协变，特别是与通过视觉到听觉感觉替代装置的感知引发的枕部激活的协变。我们预测，在使用感觉替代装置的过程中，根据感知到的刺激和/或执行的任务，通常不被声音招募的大脑区域可以被激活，并与使用熟练程度相称。公共卫生相关性更好地了解盲人大脑和认知可塑性的生理机制将有助于为盲人开发更充分的康复策略和辅助设备，如视觉假体或感觉替代设备。从更广泛的角度来看，这将为我们提供关于大脑可塑性的有价值的信息，以及大脑如何修改自己的组织以应对环境限制。这可能会进一步启发脑损伤患者神经心理学和康复方法的发展。

DESCRIPTION (provided by applicant): Visual deprivation is one of the most extreme conditions leading brain regions to adopt new functions in response to environmental constraints, that is, to compensate for the loss of a sensory modality. Studies in visually deprived animals and in blind humans have long demonstrated the cross-modal recruitment of the visual cortex to process non-visual information. Yet, little is known about the functional parcellation of the reorganized occipital cortex and its precise role in the processing of non-visual information and in higher cognitive functions. The main aims of the present project are (1) to determine the sensory organization of the occipital cortex in blind subjects, (2) to identify the source of non-visual input to occipital cortex in the blind, and (3) to determine the functional role of the occipital cortex of blind subjects in the processing of non-visual stimuli, particularly when using a sensory substitution device. Using functional Magnetic Resonance Imaging (fMRI), we will examine brain activity related to tactile and auditory stimulation while subjects try to either identify or localize stimuli. This will allow us to determine whether domain specificity exists within the reorganized occipital cortex for sensory modality and/or for identification and localization. Using Diffusion Tensor Imaging (DTI) and Voxel-Based Morphometry (VBM), two relatively novel structural MRI techniques, we will investigate the structural basis of cerebral adaptive changes in blind subjects. VBM will allow us to examine if grey-matter cell density and volume in the blind occipital cortex are the same as those in the occipital cortex of sighted persons; DTI will examine the strength of white-matter fiber tracts projecting to and from occipital cortex in both subject groups, thus determining relative changes in the source of non-visual input in the blind. To test to what extent blindness is accompanied by enhanced non-visual abilities and to determine the functional role of occipital cortex in the blind, we will supplement brain imaging with extended psychophysical evaluations. We will examine the co-variance of behavioral performance with activation of brain regions by tactile or auditory stimulation, and in particular with occipital activation elicited by perception through a visual- to-auditory sensory substitution device. We predict that brain areas that are normally not recruited by sounds can be activated during the use of the sensory substitution device according to the stimuli perceived and/or the task performed and commensurate with proficiency of use. PUBLIC HEALTH RELEVANCE A better understanding of the physiological mechanisms underlying brain and cognitive plasticity in blindness will help to develop more adequate rehabilitation strategies and assistive devices for the blind, such as visual prostheses or sensory substitution devices. In a wider perspective, this will provide us with valuable information regarding brain plasticity in general and how the brain modifies its own organization in response to environmental constraints. This could further inspire the development of neuropsychological and rehabilitation methods for patients with brain injuries.