视觉与触觉认知在低视力患者中的交互作用研究

Vision, as one of the most important and critical sensation in human, also works together with other senses for recognizing the outer world and performing daily tasks. Visual impairment could lead to adaptive changes in the brain, change the model of integration and weighting between different senses, and even enhance the function of a substitutive sensory modality such as touch. Previously, people have reported that tactile perception could activate visual cortex in blind subjects and blind subjects also seem to have better tactile acuity. In the meanwhile, in normally sighted subjects, there is also interaction between visual and tactile perception and some areas in the brain that were traditionally known as exclusively visual driven can actually be activated by multiple sensory modalities. However, there is very limited research on the interaction between vision and touch in low vision. Since multisensory integration could provide potential benefit for low vision rehabilitation, especially that there might be sensory enhancement between different senses, it is important to further study the interaction between vision and touch in low vision. .In order to understand the mechanism of tactile functional changes and cross-modal cortical reorganization after vision loss, we need to learn, first how touch and vision interact with each other and why the visual areas could be activated by tactile perception in the intact visual system, and second how visual impairment would change the model of interaction between vision and touch and lead to cross-modal cortical reorganization. In the visual system, visual stimuli can be divided into components of different features; similarly, tactile stimuli also have different features and dimensions, such as spatial frequency, orientation, and size, etc. It is important to know the effect of different features on the interaction between vision and touch. Previously, we have studied the activation pattern in visual cortex with tactile stimuli using the method of fMRI multivoxel pattern analysis (MVPA) and showed that the multivoxel pattern in visual cortex is related to the specific feature that is presented. .Here in this project, we will test the tactile function and interaction between touch and vision in low vision subjects using the methods of fMRI and psychophysics. Specifically, we will study: 1. whether there is functional enhancement in touch and the brain activation pattern (decoding efficiency) using the method of fMRI MVPA, 2. and how touch and vision interact with each other and the cortical site of the multisensory interaction. The results of this study will help us better understand how visual impairment affected different sensory modalities and the mechanism of cortical reorganization; provide guidance for low vision rehabilitation and artificial vision application. This project will also push forward the interdisciplinary research in ophthalmology, medical imaging and neuroscience.

视觉是人类最重要的感知觉之一，同时人类对外界的认知还依赖于不同感知觉的整合。眼病损伤视觉信号，导致大脑发生适应性改变甚至出现重塑,然而过去此类研究主要集中于全盲人群。鉴于低视力的高发病率以及视触觉交互作用对低视力功能康复的重要意义，本项目将对低视力的视觉与触觉交互作用进行研究。我们目前研究发现触觉可以激活正常视觉系统多个视觉功能区，并且功能磁共振多体素解码分析提示其激活具有刺激相关特异性。本项目拟采用功能磁共振和心理物理学方法，研究： 1、低视力触觉识别的功能改变以及触觉刺激在视觉皮层激活的功能意义；2、视觉与触觉交互作用模式的改变及其在大脑皮层的发生位置，阐明视觉损害程度和发病年龄对触觉、视觉交互作用及皮层重塑的影响。研究结果将为低视力康复提供指导意义并为人工视力提供神经基础，同时也加深对大脑重塑机制的了解，促进眼科学、影像学、认知科学等多个学科的交叉研究进展。

本项目以低视力的视觉皮层重塑为研究主题，着重选取了晚期青光眼患者，因为青光眼是造成不可逆盲的首要病因之一， 视功能损伤无法逆转，低视力康复尤显意义重大。本任务书中提出低视力患者的视觉皮层重塑是低视力康复的一个可能手段，研究中我们针对晚期青光眼展开了三个方面的研究：视觉皮层重塑、视觉通路白质纤维改变以及视觉与触觉交互作用的跨感知觉皮层重塑。.晚期青光眼的视觉皮层重塑研究：晚期青光眼视野严重缺损，视觉皮层出现大片失去传入信息的病变投射区。研究发现在主动注视的条件下，视觉皮层的病变投射区出现了功能性重塑。这种功能性重塑可能与主动注视条件下的视觉注意分布、视觉想像构建有关。与黄斑变性不同的是，青光眼损伤视网膜神经节细胞，并且损伤范围广泛，因此该研究结果进一步提示视觉皮层能够出现大范围、长程的重塑。 视觉皮层的重塑仅见于双眼视野缺损患者而非单眼视野缺损患者，提示周边视野应用的必要性，进一步提示了周边视野的康复训练的重要性。.晚期青光眼的视觉通路改变：青光眼的主要病理改变是视网膜神经节细胞的损伤，进而造成上行神经纤维的损害。当上行神经纤维的损害达到一定程度后，将对未来视觉假体的应用带来困难，因此晚期青光眼患者的视觉通路改变研究具有重要意义。本项目应用弥散张量成像的方法研究晚期青光眼患者的视觉通路白质纤维改变， 研究结果显示晚期青光眼的视束、视放射均出现了改变，不同于视束与视放射，枕叶胼胝体的弥散属性在病例组与正常对照组间未观察到显著差异，提示青光眼尚未引起更高级的视觉通路的白质纤维损伤。
在此基础上，纤维追踪成像以及自动纤维定量分析的方法进一步提示视束与视放射的弥散属性变化存在差异。.晚期青光眼的跨感知觉皮层重塑：不同感知觉在时间和空间发生交互作用，为低视力的视觉康复提供新的途径。我们针对触觉信息的形态 、空间位置和方位等属性设计了一系列触觉刺激，研究被试对触觉刺激进行辨别时视觉皮层是否激活，并进一步采用MVPA的方法观察数据。我们发现主要是枕叶外侧和颞叶腹侧视觉皮层的激活信号存在与各类触觉刺激对应的激活模式，而初级视觉皮层的这种表现仅见于与空间布局的这一触觉任务。这种视觉皮层的跨感知觉重塑尤其是MVPA可解码的功能激活模式在晚期青光眼患者进一步加强。这个发现提示传统意义上的部分视觉皮层可能本身就是多感知觉皮层，视觉信息减弱后可进一步依赖于触觉信息而出现跨感知觉皮层重塑的加强。