【作者】 田银；

【导师】 尧德中；

【作者基本信息】 电子科技大学 ， 生物医学工程， 2010， 博士

【摘要】 视觉空间注意定向是大多数生物及人类最基本的功能之一,它在快速的目标搜索中具有重要意义。空间定向包括两种机制:内源和外源定向。内源定向是指有目的地分配注意资源到预先计划的空间位置,而外源定向则是对突出性事件的反射性自动反应。对于外源定向,其线索化位置最初的易化效应被归功于外周线索吸引注意的结果,而后对线索化位置的反应减慢被称为返回抑制(inhibition of return, IOR)。IOR通常采用经典的空间线索化范式进行研究。在这类实验中,当线索靶刺激间隔时间(stimulus onset asynchrony, SOA)小于250ms时被试对线索化位置的靶刺激反应快于非线索化位置,而当SOA大于250ms时,则表现为对线索化位置的一个慢反应。它表征了对线索化位置及其附近的突出刺激的反应执行减弱,以此来抑制注意重新定向到线索化位置。该效应最初被认为是阻碍注意返回先前搜索过的位置。自Posner和Cohen报道该效应以来,IOR已成为空间定向研究中的一个重要成分,并成为一个颇有争议的研究热点。各种不同的技术应用于IOR相关的研究,主要包括行为学研究、事件相关电位(event-related potentials, ERPs)研究、功能磁共振成像(functional magnetic resonance imaging, fMRI)研究、经颅磁刺激(transcranial magnetic stimulation, TMS)研究、单细胞记录(signal-cell recording)、正电子断层扫描成像(positron emission computerized topography, PET)等。本论文围绕视觉空间定向中返回抑制的脑机制问题,利用高时间分辨率的事件相关电位(ERPs),及其低分辨率层析成像(low resolution brain electromagnetic tomography, LORETA)源定位技术,和高空间分辨率的功能磁共振技术等,对该问题进行了深入、细致、有创新性的研究。所做的主要工作与成果如下:1、视觉空间线索化效应的动态脑机制研究在cue-target范式中,研究了由外周非信息化线索所引起的脑电,并将其结果分阶段进行了LORETA定位。与以往采用ERP研究IOR的方式不同的是,在本研究中我们关注的是由靶刺激出现前的线索所激活的脑区的时间特性。这些结果显示:在线索出现后,相关的激活大致可以分为三个阶段:早阶段(110ms-240ms)的激活为前额叶皮层,顶内皮层,以及对侧枕颞皮层。中阶段(240ms-350ms)的激活主要分布在额叶皮层和顶叶皮层。晚阶段(350ms-650ms)的主要激活在枕顶皮层,但与第一阶段不同的是激活区域转移到线索化位置的同侧。这些发现表明,IOR与注意和动作反应都有关,最初的易化和IOR在时程上是共存的,并受两种神经网络调制。最后我们提出了一个计时器模型将IOR的空间机制延伸到一个时空机制。2、基于按键反应抑制的返回抑制脑机制研究采用非信息外周线索化Go/Nogo任务实验,通过ERPs的早成分(P1和N1)和晚成分(Go/Nogo N2和P3)来刻画IOR的神经机制。头表拓扑地形图和LORETA显示,线索化效应调制的早成分主要分布在背侧枕顶区域;晚成分主要分布在额叶中部区域。Nogo-N2在有效试验中比在无效试验中出现得早且其幅度也相对要小,这种现象表明,IOR相关的晚成分被反应准备抑制所调制。Nogo-P3在有效中比在无效中出现得迟且其幅度相对要大,该结果表明额叶眼区(FEF,frontal eye field)在线索化位置有一个解标记的过程。这些证据表明,IOR的机制既包括感觉抑制也包括反应抑制。3、空间定向和按键抑制交互效应的脑机制研究以前的研究报道前额叶皮层(PFC, prefrontal cortex),包括背侧PFC(DLPFC)、额下回(IFC,inferior frontal cortex )、额中回内侧(MFC,medial frontal cortex)和前扣带回(ACC,the anterior cingulate cortex)在按键反应抑制中起重要作用。然而,对于相关脑区是如何调制空间定向和控制冲突的交互效应却仍然不清楚。因此,本研究中采用事件相关fMRI技术来研究空间定向和反应抑制的交互效应所涉及的不同神经机制。两类图形(按键刺激和抑制按键刺激)随机呈现在线索化或非线索化位置。内源反应抑制激活大范围皮层,包括两侧颞顶连接区域(TPJ, temporoparietal junctions)、两侧额上回(superior frontal gyrus)、右侧颞上回(superior temporal gyrus)、以及额下回(inferior frontal gyrus)。与之相反,外源反应抑制仅仅激活右侧额上回和右侧额中回。同时在本研究中也涉及到空间定向的时程效应,内源定向的时程效应主要体现在两侧MiFG (middle frontal gyrus)和MeFG(medial frontal gyrus)的激活,而外源定向的时程效应主要体现在两侧的MiFG激活。这些结果表明在不同的定向情况下,反应抑制所涉及到的脑区不同,则它们可能反应的是分离的加工过程。4、视觉搜索任务中的返回抑制脑机制研究外源定向被认为是反射性的自动加工过程。它最初表现为易化效应然后被一个延时的反应(IOR)所替代。然而,对于外源易化和IOR是一个加工过程的两个阶段还是两个相互独立的加工过程仍然不清楚。一些研究采用保持内源注意的方法来研究IOR,发现易化和IOR是相互独立的过程。到目前为止,很少有报道探讨外源注意易化和IOR的相互关系。在本研究中,我们利用高时间分辨率的ERP技术在视觉搜索任务中对外源易化和IOR的关系进行了研究。当外源注意保持在序列搜索位置上时仍然获得了一个延时(IOR),伴随此行为的有三个ERP成分:后顶的Pd200、前额叶的Nd240、和两侧TPJ的Nd280。当外源注意保持在平行搜索后的位置时,获得了一个快反应(外源易化效应)。同时发现了一个ERP成分:枕顶中部的Nd280。这些结果表明外源易化和IOR涉及不同的脑区和/或神经过程,它们可能反映的是独立的和分离的加工过程。更多还原

【Abstract】 The orienting of visual-spatial attention, which is fundamental to most organisms, plays an important role in rapid and efficient search of visual environments. This process is thought to include two mechanisms: endogenous and exogenous orienting. Endogenous orienting refers to the purposeful allocation of attentional resources to a predetermined location in space, whereas exogenous orienting is thought to be triggered reflexively and automatically by an abrupt onset event. The early benefit of exogenous orienting at the cued location is usually attributed to the capture of attention by the peripheral cue, and the subsequent decline in performance at the cued location has been referred to as inhibition of return (IOR).IOR is studied by using the typical spatial cue-target paradigm. In such an experiment, subjects respond faster to a target presented at a cued location than that at an uncued location when a stimulus onset asynchrony (SOA) between cue and target is shorter than 250 ms, whereas subjects respond slower to a target appearing at a cued location than that at an uncued location when SOA is longer than 250 ms. IOR is thought to represent a decline in salience in the vicinity of the cue that discourages re-orienting back to the cued location. The primary assumed mechanism is that attention is inhibited from returning to previously searched locations. Since Posner & Cohen’s seminal study, IOR has become an actively investigated component of orienting, and has been a hot topic of many debates.Various technologies are employed to the studies related to IOR. These include behavioral studies, event-related potentials (ERPs), functional magnetic resonance imaging (fMRI), transcranial magnetic stimulation (TMS), signal-cell recording, positron emission computerized topography (PET) and so on.This dissertation focuses on the studies of brain mechanisms of IOR by high temporal resolution ERPs with the source localization of low resolution electromagnetic tomography (LORETA) and high spatial resolution fMRI respectively. A series of multilevel, novel and detailed researches on IOR have been carried out. Our major works and achievements are listed as below:1、A study on the dynamic brain mechanism of visual spatial-cueing effectWithin the cue-target paradigm, this study analyses the ERPs elicited by the peripheral uninformative cue and uses LORETA to localize the results of the different processing stages. Unlike previous ERP investigations of IOR, in this study we focus on the time characteristic of the neural activity (via EEG) elicited by the cue prior to the appearance of the target. The results show that after cue onset, activations may be approximately divided into three stages. In the early stage (110ms-240ms), activations are in the prefrontal cortex, the intraparietal cortex, and the contralateral occipito-temporal cortex. In the middle stage (240ms-350ms), activations are mainly in the frontal cortex and the parietal cortex. In the late stage (350ms-650ms), the main activations are in the occipito-parietal cortex. Unlike the early stage, the activation areas shift to the ipsilateral side of the cued location. These findings indicate that IOR is related to both attention and motor response, and also suggest that the time course of initial facilitation and IOR is concurrent and mediated by two neural networks. Finally, a time table is proposed, which extends the spatial mechanism of IOR to a spatio-temporal mechanism.2、A study on the brain mechanism of IOR based on the response inhibitionWith an uninformative peripheral cued Go/Nogo task experiment, this study aims to characterize the neural mechanism of IOR by both early (P1 and N1) and late (Go/Nogo N2 and P3) ERPs. The scalp topographies and LORETA show that the changes of the early ERPs, the cueing effects, are distributed mainly over the dorsal occipito-parietal areas. The changes of the late ERPs are distributed mainly over the frontocentral areas. The Nogo-N2 is earlier and smaller in valid trials than in invalid trials, which suggests that the late components related to IOR are modulated by response preparation inhibition. The Nogo-P3 is later and larger in valid trials than that in invalid trials, indicating that the frontal eye field(FEF)is free from an inhibitory marker in the cued locations. These evidences suggest that the mechanism of IOR consists of both the sensory inhibition and the response preparation inhibition. 3、A study on the brain mechanism of interaction between spatial orienting and response inhibitionThe previous studies have suggested that the prefrontal cortex (PFC), including dorsolateral prefrontal cortex (DLPFC), inferior frontal cortex (IFC), medial frontal cortex (MFC) and the anterior cingulate cortex (ACC), plays an important role in response inhibition in Go/Nogo tasks. However, it remains unclear how these“executive”brain regions will act when the conflict control process interacts with spatial orienting. Therefore, event-related fMRI is used to investigate the differential neural mechanisms underlying interactions between spatial orienting and response inhibition. Two types of figures (go stimulus and Nogo stimulus) are random presented either at the cued location or uncued location. Endogenous response inhibition activates widespread cortical regions including bilateral temporoparietal junctions, bilateral superior frontal gyrus, right superior temporal gyrus, and inferior frontal gyrus. Conversely, exogenous response inhibition activates only two areas including right superior frontal gyrus and right middle frontal gyrus. Meanwhile, the interaction of the timecourse in spatial orienting has been investigated in this study. The timecourse of endogenous orienting indicates activations in the medial frontal gyrus, whereas the timecourse of exogenous orienting indicates activations in the bilateral middle frontal gyrus. These results show that response inhibition in different orienting involves different brain areas, thus they are quite possibly two dissociable processes.4、A study on the brain mechanism of IOR in visual search tasksExogenous orienting is considered to be a reflexive and automatic process. It initiates facilitation, which is then replaced by a delayed response (i.e. IOR). However, it is still unclear whether the initial facilitation and the later IOR are two stages of one process or simply two independent processes. Some studies have observed IOR when endogenous attention is fixed and found that these processes are driven by separate mechanisms. To date, however, few studies have directly addressed the relationship between exogenous attention facilitation and IOR. Here, we investigate the different effects of exogenous facilitation and IOR in visual search tasks by recording ERPs with high temporal resolution. When exogenous attention remains to be fixed at the serial search locations, a delayed response is observed (i.e. IOR) with three ERP components: a Pd200 at the posterior parietal areas, an Nd240 at the middle tended to left prefrontal areas and an Nd280 at the bilateral temporoparietal areas. When exogenous attention stays at parallel search locations, a faster response is observed (exogenous facilitation). Here, one ERP component appears, an Nd280 at the middle occipito-parietal areas. These results suggest that the exogenous facilitation and IOR involve different brain areas and/or neural processes, and are therefore most likely two dissociable processes.更多还原