静息状态默认脑活动网络的初步检验——听觉呈现语言任务

目的利用fMRI技术,通过听觉呈现语言任务,探讨刺激呈现通道对负激活脑区的影响,进一步检验静息状态人脑默认活动假说。方法13名健康成年志愿者参加实验。进行2次fMRI实验。实验1（简单任务）任务期要求受试者听无意义假词;实验2（复杂任务）要求受试者听真词并作词语属性判断（具体或抽象）。静息期要求受试者闭眼、静卧,不要做任何主动思维活动。利用SPM2软件进行数据处理。先分析单个被试,然后行组间比较。采用反减法获得负激活图。并把本次实验结果与以往视觉呈现任务结果进行比较。结果初级视觉皮层与初级听觉皮层的负激活存在明显的通道依赖性,听觉呈现刺激引起视觉皮层负激活,视觉呈现刺激时听觉皮层表现为负激活。非任务依赖性负激活脑区包括扣带回后部/楔前叶（BA31/30）、扣带回前部（BA24/32）、两侧颞上回（BA8）、两颞下回前部（BA20）、两侧顶下小叶（BA39/40）。这些区域的负激活与刺激呈现通道方式及特定刺激任务无关。该负激活脑区模式与人类默认脑活动网络基本一致。结论刺激呈现通道是影响任务依赖性负激活的因素之一,探讨负激活问题时应该考虑到这一因素。同时,本研究进一步验证了静息状态时人脑默认活动假说。     

单侧感音神经性耳聋病人听觉中枢的fMRI研究

目的探讨单侧感音神经性耳聋病人与正常听力者的听皮质频率敏感性排列结构的差异;双侧听皮质中枢半球优势的变化;单侧感音神经性耳聋病人皮层下区听觉传导通路的变化.方法20例正常志愿者和20例单侧感音神经性耳聋病人,分别采集T1WI、GRE-EPI及3D GRE T1WI影像.采用组块式方法分别随机给予500 Hz,4000 Hz两种纯音刺激,每种刺激重复2次.所有图像均经AFNI进行后处理,统计阈值概率设定为P＜10-5,激活范围阈值设定为半径5 mm,体积300 mm3的连续激活区域考虑为有意义激活区.结果正常听力者和单侧耳聋病人给予单耳500 Hz,4000 Hz刺激时,二者对于听皮质激活容积存在统计学差异(P＜0.05).正常听力者给予单耳刺激表现为对侧半球优势,半球激活容积比分别为7.56,6.02(右耳刺激);2.56,5.11(左耳刺激).而单侧耳聋病人则表现为同侧半球优势,半球激活容积比分别为0.62,0.69(左侧耳聋,右耳刺激);0.96,0.83(右侧耳聋,左耳刺激).结论正常听力者对500 Hz和4000 Hz的频率刺激激活区的位置存在差别.单侧感音神经性耳聋失去了听觉中枢的频率敏感性空间排列结构.单侧耳聋病人表现为同侧半球优势.500 Hz对正常听力者和单侧感音神经性耳聋病人的听皮质激活范围明显大于4000 Hz者.     

静息态功能磁共振成像观察正常人听觉皮层功能

目的 探讨正常人听觉皮层与全脑的正相关及负相关的功能连接.方法 采用静息态下平面回波成像技术采集44名健康受试者fMRI数据,分别以左侧及右侧AⅠ区为种子点,用功能连接的方法观察左、右大脑初级听觉皮层与全脑的正相关及负相关功能连接脑图.结果 分别以双侧AⅠ区为种子点时,正激活的脑网络主要包含双侧AⅠ、AⅡ、岛叶、辅助运动区及扣带回,以同侧为主;与右侧AⅠ区相关的正激活脑区还包括同侧背侧丘脑.与双侧AⅠ区相关的负激活脑网络与脑默认网络大体一致,主要包括双侧后扣带回/楔前叶、额叶内侧回、顶下小叶,双侧小脑半球可见明显激活.结论 静息态磁共振功能连接可满意显示听觉皮层的连接脑图.正相关功能连接主要局限在听觉系统内,负相关功能连接类似于默认网络.     

耳鸣患者脑听觉激活区BOLD-fMRI的研究

目的:分析应用BOLD-fMRI观察耳鸣患者的脑听觉激活区情况。方法:从我院选取2018年7月-2019年7月收治的20例耳鸣患者作为观察组,采用BOLD-fMRI检查方式,对耳鸣患者的大脑听觉皮质区激活信号进行观察,选择20例健康者作为对照组,分析的对照组健康者与观察组耳鸣患者用纯音刺激单耳时,听觉皮质激活区的情况。结果:20例健康者的颞叶区,经纯音刺激后出现激活反应,且在健康者的颞叶区的颞上回部位的激活率最高,在对侧听觉皮质激活中,刺激单耳时其激活体积及信号强度明显比同侧更高(P<0.05),主要表现出对侧的半球传导优势。在纯音刺激耳鸣患者时其大脑皮质激活区的激活体积、信号强度及解剖部位规律混乱。结论:应用BOLD-fMRI对耳鸣患者进行观察,发现在其听觉皮质区的神经活动存在异常现象。     

人脑运动皮层功能磁共振成像研究

目的采用功能用磁共振成像（fMRI）回波平面（EPI）技术,研究人脑运动皮质血氧水平依赖（BOLD）的功能磁共振成像。方法27名正常健康志愿者,右手挤压橡皮圈,在运动和静止两种对比条件下,采集运动皮层的回波平面图像（BOLD-fMRI）。分析运动状态和非运动状态信号对比的脑功能图像。结果fMRI图像显示运动刺激下脑功能活动激活区主要位于对侧感觉运动皮质区、辅助运动区等。结论fMRI可用于研究活体人脑各功能区的活动,fMRI可对运动刺激下的人脑运动皮质进行初步定位。     

人脑视觉皮质功能磁共振成像研究

目的研究人脑视觉皮质血氧水平依赖（BOLD）的功能磁共振成像。方法18名正常健康志愿者，在光刺激和非刺激的两种对比条件下，采用EP1技术，采集视觉皮质血氧水平依赖（BOLD）图像。t检验分析得出光刺激状态和非刺激状态信号对比的脑功能图像。结果fMRI图像显示光刺激下脑功能活动激活区主要位于双侧视觉皮质区。结论fMRI可用于在活体人脑上研究各功能区活动，光刺激下的fMRI可对人脑视觉皮质进行定位。     

颞侧偏盲患者单眼水平半视野刺激的fMRI研究

目的：观察正常人单眼水平半视野刺激下视觉皮层的激活形式;探讨fMRI用于评价颞侧偏盲患者初级视觉皮层激活形式的可能性。资料与方法：对13例颞侧偏盲的垂体大腺瘤患者和15名正常志愿者进行组块设计的fMRI实验,所有受试者分别接受左眼颞侧、左眼鼻侧、右眼颞侧和右眼鼻侧视野刺激,刺激内容为水平单侧40°黑白翻转棋盘格,对照内容为黑色屏幕中心的白色“＋”。采用1.5T MR扫描仪采集数据,采用SPM　2软件进行后处理,获得对照组各种刺激下的平均激活图,分析患者组视野缺损与初级视觉皮层激活形式之间的对应关系。结果：在排除了扫描过程中头动及噪声影响后,患者组和对照组最终各入组10例。对照组单眼颞侧视野刺激时表现为对侧视觉皮层激活,鼻侧视野刺激时表现为同侧初级视觉皮层激活为主。患者组在接受颞侧视野刺激时双侧视觉皮层均未见激活,而给予鼻侧视野刺激时均表现为同侧视觉皮层激活。结论：正常情况下视野与初级视觉皮层之间存在对应关系,颞侧偏盲患者表现为以对侧初级视觉皮层激活下降为主,fMRI是反映视交叉异常对视觉皮层影响的有效方法。     

垂体大腺瘤患者视觉皮层的fMRI观察

目的 采用fMRI方法评价垂体大腺瘤患者视觉中枢的激活形式,观察视野改变与初级视觉皮层功能变化之间的关系.方法 对23例伴视交叉受压的垂体大腺瘤患者及18名正常志愿者的左右眼分别进行组块设计的fMRI实验,刺激内容为全视野黑白翻转棋盘格,对照内容为黑色屏幕中心的白色"+",6个对照组块与5个刺激组块交替进行,每个组块20 s.采用1.5T MR扫描仪.数据后处理采用SPM2软件.采用两样本t检验的组间分析方法分别获得左眼及右眼刺激下患者组与对照组间的激活差异图.分析患者视野缺损类型与初级视觉皮层激活形式之间的对应关系.结果 在严格控制头动和机械噪声等影响因素后,最终左、右眼刺激各入组12例.患者组与对照组比较,初级视觉皮层激活范围及强度均明显缩小,左眼刺激时患者组以右侧初级视觉皮层激活下降为主,右眼刺激时患者组以左侧初级视觉皮层激活下降为主.6例患者表现为典型左颞侧视野缺损,左眼刺激时表现为左侧初级视觉皮层激活,而右侧激活明显下降或无激活.7例患者为典型右颞侧视野缺损,右眼刺激时表现为右侧初级视觉皮层激活,而左侧激活明显下降或无激活.结论 垂体大腺瘤患者初级视觉皮层的激活形式与视野缺损类型存在对应关系,颞侧视野缺损主要以对侧初级视觉皮层激活下降为主.fMRI是研究前视路病变对视觉中枢皮层影响的有效方法.     

首发精神分裂症听觉感觉门控异常的功能磁共振研究

目的通过功能磁共振成像(fMRI)技术探讨首发精神分裂症听觉感觉门控异常与脑功能异常激活之间的关系,为该病的临床研究提供更多客观依据。方法选择2011年6月至2012年6月精神科收治的15例首发精神分裂症患者作为研究组,同时选取年龄、性别、受教育程度相匹配的15例志愿者作为正常对照组,两组均进行脑功能磁共振成像,采用多声音刺激和单声音刺激比较的范式,比较两组患者感觉听觉门控的异常。结果研究组听觉感觉门控脑激活在右侧海马、右侧丘脑区明显低于正常对照组,差异有统计学意义(P<0.05)。结论首发精神分裂症患者的听觉门控异常可能与大脑海马、丘脑等功能激活异常有关。     

震动触觉刺激fMRI评价先天性耳聋婴幼儿听觉及语言中枢功能的可行性

目的 评价震动触觉刺激fMRI在先天性极重度耳聋婴幼儿听皮质、语言中枢功能检测中的可行性。方法 选取先天性极重度感音神经性耳聋患儿19例(聋儿组)及听力正常幼儿7名(对照组),分别采集轴位SE T1WI、GRE-EPI fMRI以及全脑三维扫描影像。采用组块设计方法分别给予右小腿近踝部震动触觉刺激。所有图像均采用统计参数图5(SPM5)进行后处理,利用SPM5二次统计模块进行聋儿组与对照组的组内分析和组间比较。结果 聋儿组患儿在给予右小腿近踝部震动触觉刺激时,双侧颞横回、颞上回(BA41区、BA42/22区)可见明显激活。对照组在给予相同刺激时听觉中枢激活不明显。语言中枢包括额中回、额下回、颞上回、颞中回、角回,可见明显激活。聋儿组与对照组进行组间比较发现,聋儿组数据减去对照组数据时可见激活的脑区主要有双侧颞横回、双侧颞上回。结论 震动触觉刺激fMRI可用于评价先天性感音神经性耳聋婴幼儿听觉及语言相关脑区功能。     

Functional anatomy of pitch memory--an fMRI study with sparse temporal sampling

Auditory functional magnetic resonance imaging tasks are challenging since the MR scanner noise can interfere with the auditory stimulation. To avoid this interference a sparse temporal sampling method with a long repetition time (TR = 17 s) was used to explore the functional anatomy of pitch memory. Eighteen right-handed subjects listened to a sequence of sine-wave tones (4.6 s total duration) and were asked to make a decision (depending on a visual prompt) whether the last or second to last tone was the same or different as the first tone. An alternating button press condition served as a control. Sets of 24 axial slices were acquired with a variable delay time (between 0 and 6 s) between the end of the auditory stimulation and the MR acquisition. Individual imaging time points were combined into three clusters (0-2, 3-4, and 5-6 s after the end of the auditory stimulation) for the analysis. The analysis showed a dynamic activation pattern over time which involved the superior temporal gyrus, supramarginal gyrus, posterior dorsolateral frontal regions, superior parietal regions, and dorsolateral cerebellar regions bilaterally as well as the left inferior frontal gyrus. By regressing the performance score in the pitch memory task with task-related MR signal changes, the supramarginal gyrus (left>right) and the dorsolateral cerebellum (lobules V and VI, left>right) were significantly correlated with good task performance. The SMG and the dorsolateral cerebellum may play a critical role in short-term storage of pitch information and the continuous pitch discrimination necessary for performing this pitch memory task.     

Amplitopicity of the human auditory cortex: an fMRI study

Whereas specialized frequency-encoding patterns in the human auditory cortex are generally accepted, termed tonotopicity, a similar principle of intensity encoding--amplitopicity--is debated controversially. This functional magnetic resonance imaging study describes the relationship of the activation volume and the spatial distribution of activated clusters under different sound pressure levels (SPL) across the temporal plane including the transverse temporal gyrus (TTG). Nine healthy subjects with no hearing deficiencies were investigated using an echo-planar imaging technique at 1.5 T. A boxcar stimulation paradigm was applied with a 5-Hz pulsed sine tone of 1000 Hz frequency at three SPLs of 70, 82, and 90 dB. Linear cross-correlation analysis (correlation coefficient > 0.3 corresponding to P < 0.08) of the functional data set revealed bilateral BOLD response within the auditory cortex of the nine subjects with moderate increase of activation volume for higher sound pressure levels. With increasing sound pressure a two-dimensional drift of cortical activation was observed (a) from the ventral to the dorsal edge and (b) from lateral to medial parts of TTG. This latero-medial drift therefore mimics the well-accepted principle of tonotopy for frequency-encoding neurons. This study demonstrates the existence of an amplitopic pattern of intensity-encoding neuronal clusters that in part resembles the tonotopic distribution of frequency-encoding neurons. This finding has to be integrated into the understanding of the auditory organization for the interpretation of higher auditory functions such as sound perception or speech.     

Functional fields in human auditory cortex revealed by time-resolved fMRI without interference of EPI noise

The gradient switching during fast echoplanar functional magnetic resonance imaging (EPI-fMRI) produces loud noises that may interact with the functional activation of the central auditory system induced by experimental acoustic stimuli. This interaction is unpredictable and is likely to confound the interpretation of functional maps of the auditory cortex. In the present study we used an experimental design which does not require the presentation of stimuli during EPI acquisitions and allows for mapping of the auditory cortex without the interference of scanner noise. The design relies on the physiological delays between the onset, or the end, of stimulation and the corresponding hemodynamic response. Owing to these delays and through a time-resolved acquisition protocol it is possible to analyze the decay of the stimulus-specific signal changes after the cessation of the stimulus itself and before the onset of the EPI-acoustic noise related activation (decay-sampling technique). This experimental design, which might permit a more detailed insight in the auditory cortex, has been applied to the study of the cortical responses to pulsed 1000 Hz sine tones. Distinct activation clusters were detected in the Heschl's gyri and the planum temporale, with an increased extension compared to a conventional block-design paradigm. Furthermore, the comparison of the hemodynamic response of the most anterior and the posterior clusters of activation highlighted differential response patterns to the sound stimulation and to the EPI-noise. These differences, attributable to reciprocal saturation effects unevenly distributed over the superior temporal cortex, provided evidence for functionally distinct auditory fields.     

BOLD fMRI investigation of the rat auditory pathway and tonotopic organization

Rodents share general anatomical, physiological and behavioral features in the central auditory system with humans. In this study, monaural broadband noise and pure tone sounds are presented to normal rats and the resulting hemodynamic responses are measured with blood oxygenation level-dependent (BOLD) fMRI using a standard spin-echo echo planar imaging sequence (without sparse temporal sampling). The cochlear nucleus (CN), superior olivary complex, lateral lemniscus, inferior colliculus (IC), medial geniculate body and primary auditory cortex, all major auditory structures, are activated by broadband stimulation. The CN and IC BOLD signal changes increase monotonically with sound pressure level. Pure tone stimulation with three distinct frequencies (7, 20 and 40 kHz) reveals the tonotopic organization of the IC. The activated regions shift from dorsolateral to ventromedial IC with increasing frequency. These results agree with electrophysiology and immunohistochemistry findings, indicating the feasibility of auditory fMRI in rats. This is the first fMRI study of the rodent ascending auditory pathway.     

Functional MRI of auditory cortex activated by multisite electrical stimulation of the cochlea

Electrical stimulation of the ear of deaf patients via cochlear implants offers a unique occasion to study activity of central auditory pathways with fMRI, without bias due to scanner noise. Such measurements, however, require one to control the possible interference between fMRI acquisition and the implanted electrodes. A series of measurements on a customized phantom designed to characterize the level of induced currents during MRI acquisition is presented. These experiments demonstrate that the major artifactual contribution is due to radiofrequency interaction and that safe experimental conditions can be obtained with proper shielding of the stimulation cables. The induced currents could be reduced to low levels (<50 microA for a duration <2 ms), below the acoustic perceptual threshold of cochlear implant subjects. Subsequent fMRI experiments on a patient using an Ineraid cochlear implant were conducted. Results revealed bilateral localized activation of the primary auditory cortex. Stimulation of two different intracochlear electrodes elicited activity in two neighboring, but different, regions, in agreement with the known tonotopical organization of the auditory cortex. This work paves the way for fMRI studies of a broad selection of auditory paradigms without interference from unwanted noise.     

Representation of lateralization and tonotopy in primary versus secondary human auditory cortex

Functional MRI was performed to investigate differences in the basic functional organization of the primary and secondary auditory cortex regarding preferred stimulus lateralization and frequency. A modified sparse acquisition scheme was used to spatially map the characteristics of the auditory cortex at the level of individual voxels. In the regions of Heschl's gyrus and sulcus that correspond with the primary auditory cortex, activation was systematically strongest in response to contralateral stimulation. Contrarily, in the surrounding secondary active regions including the planum polare and the planum temporale, large-scale preferences with respect to stimulus lateralization were absent. Regarding optimal stimulus frequency, low- to high-frequency spatial gradients were discernable along the Heschl's gyrus and sulcus in anterolateral to posteromedial direction, especially in the right hemisphere, consistent with the presence of a tonotopic organization in these primary areas. However, in the surrounding activated secondary areas frequency preferences were erratic. Lateralization preferences did not depend on stimulus frequency, and frequency preferences did not depend on stimulus lateralization. While the primary auditory cortex is topographically organized with respect to physical stimulus properties (i.e., lateralization and frequency), such organizational principles are no longer obvious in secondary and higher areas. This suggests a neural re-encoding of sound signals in the transition from primary to secondary areas, possibly in relation to auditory scene analysis and the processing of auditory objects.     

Lateralization, connectivity and plasticity in the human central auditory system

Although it is known that responses in the auditory cortex are evoked predominantly contralateral to the side of stimulation, the lateralization of responses at lower levels in the human central auditory system has hardly been studied. Furthermore, little is known on the functional interactions between the involved processing centers. In this study, functional MRI was performed using sound stimuli of varying left and right intensities. In normal hearing subjects, contralateral activation was consistently detected in the temporal lobe, thalamus and midbrain. Connectivity analyses showed that auditory information crosses to the contralateral side in the lower brainstem followed by ipsilateral signal conduction towards the auditory cortex, similar to the flow of auditory signals in other mammals. In unilaterally deaf subjects, activation was more symmetrical for the cortices but remained contralateral in the midbrain and thalamus. Input connection strengths were different only at cortical levels, and there was no evidence for plastic reorganization at subcortical levels.