Impaired semantic processing during sentence reading in children with dyslexia: combined fMRI and ERP evidence

Developmental dyslexia is a specific disorder of reading acquisition characterized by a phonological core deficit. Sentence reading is also impaired in dyslexic readers, but whether semantic processing deficits contribute is unclear. Combining spatially and temporally sensitive neuroimaging techniques to focus on semantic processing can provide a more comprehensive characterization of sentence reading in dyslexia. We recorded brain activity from 52 children (16 with dyslexia, 31 controls) with functional magnetic resonance imaging (fMRI) and event-related potentials (ERP) in two separate counterbalanced sessions. The children silently read and occasionally judged simple sentences with semantically congruous or incongruous endings. fMRI and ERP activation during sentence reading and semantic processing was analyzed across all children and also by comparing children with dyslexia to controls. For sentence reading, we analyzed the response to all words in a sentence; for semantic processing, we contrasted responses to incongruous and congruous endings. Sentence reading was characterized by activation in a left-lateralized language network. Semantic processing was characterized by activation in left-hemispheric regions of the inferior frontal and superior temporal cortex and by an electrophysiological N400 effect after 240 ms with consistent left anterior source localization. Children with dyslexia showed decreased activation for sentence reading in inferior parietal and frontal regions, and for semantic processing in inferior parietal regions, and during the N400 effect. Together, this suggests that semantic impairment during sentence reading reduces dyslexic children's response in left anterior brain regions underlying the more phasic N400 effect and subsequently modulates the more sustained BOLD response in left inferior parietal regions.     

出声阅读条件下不规则汉字频率效应的功能磁共振成像研究

目的利用事件相关功能磁共振成像技术观察出声阅读条件下不规则汉字频率效应的脑激活模式.方法 8名非语言专业大学生在MR扫描过程中执行汉字出声阅读任务.用视觉方式随机呈现40个形声字,其中高频、低频不规则字各20个.结果左侧额中回、左侧额下回、辅助运动区、左侧颞下回后部、双侧纹外皮层、左侧岛叶、扣带回前部表现出频率效应,即阅读低频汉字时的激活强于高频汉字.结论出声阅读汉字特别是低频不规则汉字可激活主要语言加工区,可作为可靠而实用的临床诊断试验.扣带回前部与左侧额中回可能是汉字阅读的特殊脑区.     

Cortical activation during reading of ancient versus modern Japanese texts: fMRI study

The purpose of this study was to investigate human brain activity during the reading of ancient Japanese texts using functional magnetic resonance imaging. Thirty right-handed normal Japanese subjects performed two reading tasks: covert reading of (1) ancient and (2) modern Japanese text. Common areas are activated during both tasks. Activity in the left inferior frontal cortices increased during the reading of ancient Japanese text compared with the reading of modern Japanese text, whereas occipital activity increased during the reading of modern Japanese text. Our results indicate that ancient Japanese language may be processed as a foreign language.     

Phonological processing in relation to reading: an fMRI study in deaf readers

Without special education, early deprivation of auditory speech input, hinders the development of phonological representations and may alter the neural mechanisms of reading. By using fMRI during lexical and rhyming decision tasks, we compared in hearing and pre-lingually deaf subjects the neural activity in functional regions of interest (ROIs) engaged in reading. The results show in deaf readers significantly higher activation in the ROIs relevant to the grapho-phonological route, but also in the posterior medial frontal cortex (pMFC) and the right inferior frontal gyrus (IFG). These adjustments may be interpreted within the dual route model of reading as an alternative strategy, which gives priority to rule-based letter-to-sound conversion. Activation in the right IFG would account for compensation mechanisms based on phonological recoding and inner speech while activation in the posterior medial frontal cortex (pMFC) may relate to the cognitive effort called for by the alternative strategy. Our data suggest that the neural mechanisms of reading are shaped by the auditory experience of speech.     

Distinct role of spatial frequency in dissociative reading of ideograms and phonograms: An fMRI study

It has been proposed that distinct neural circuits are activated by reading Japanese ideograms (Kanji) and phonograms (Kana). By measuring high-density event-related potentials, we recently reported that spatial frequency (SF) information is responsible for the dissociation between Kanji and Kana reading. In particular, we found close links between Kana and low SF (LSF) information and between Kanji and high SF (HSF) information. However, it remains unclear which brain regions contribute to this dissociation. To determine this, we performed functional magnetic resonance imaging while presenting unfiltered or spatially filtered Kanji and Kana word stimuli to healthy native Japanese subjects. Fourier analysis revealed that Kanji and Kana stimuli were characterized by HSF and LSF information, respectively. When presented with either type of unfiltered stimulus (Kanji or Kana), the bilateral inferior temporal (IT, BA 37) regions were activated compared to the resting condition. Kana but not Kanji reading also activated the bilateral inferior parietal lobules (IPL, BA 40). When we compared Kanji and Kana reading directly, the left IT region was significantly activated by Kanji reading, while significant activation of the left IPL was observed during Kana reading. In response to filtered HSF stimuli, the Kanji reading minus Kana reading comparison revealed significant activation of the left IT region but not the left IPL. Conversely, significant activation of the left IPL but not the left IT region occurred in the Kana reading minus Kanji reading comparison for filtered LSF stimuli. These results suggest that Kanji and Kana engage a relatively overlapping network, within which the left IT is more involved in Kanji processing, while the left IPL contributes more to Kana processing. The preferential engagements of these brain regions could reflect the close links between Kana and LSF information, and between Kanji and HSF information. Therefore, this study provides further evidence that SF contributes to the dissociation between Kanji and Kana reading.     

Native and non-native reading of sentences: an fMRI experiment

The processing of syntactic and semantic information in written sentences by native (L1) and non-native (L2) speakers was investigated in an fMRI experiment. This was done by means of a violation paradigm, in which participants read sentences containing either a syntactic, a semantic, or no violation. The results of this study were compared to those of a previous fMRI study, in which auditory sentence processing in L1 and L2 was investigated. The results indicate greater activation for L2 speakers as compared to L1 speakers when reading sentences in several language- and motor-related brain regions. The processing of syntactically incorrect sentences elicited no reliably greater activation in language areas in L2 speakers. In L1 speakers, on the other hand, syntactic processing, as compared to semantic processing, was associated with increased activation in left mid to posterior superior temporal gyrus. In response to the processing of semantically incorrect sentences, both L2 and L1 speakers demonstrated increased involvement of left inferior frontal gyrus. The results of this study were compared to a previously conducted fMRI study, which made use of identical sentence stimuli in the auditory modality. Results from the two studies are in general agreement with one another, although some differences in the response of brain areas very proximal to primary perceptual processing areas (i.e. primary auditory and visual cortex) were observed in conjunction with presentation in the different modalities. The combined results provide evidence that L1 and L2 speakers rely on the same cortical network to process language, although with a higher level of activation in some regions for L2 processing.     

先天盲人“阅读”盲文的功能磁共振成像研究

目的利用磁共振功能成像显示先天盲生阅读盲文时大脑皮层的激活区,探讨盲生枕叶皮层的功能重组。方法实验组10例右利手先天盲生,分别执行盲文阅读和盲点鉴别任务。正常组大一学生10例,触摸盲文。FE-EPI采集,Medx3.2软件处理和分析,测定激活区范围和T值;比较盲人执行不同任务时和与正常组间的统计学差异。结果①10例盲生在阅读盲文时双侧主视皮层(V1)和辅助视皮层(V2、V3)激活。左右侧V1平均激活范围20和19个像素,左右侧(V2 V3)平均激活范围44和50个像素,(V2 V3)>V1。右侧(V1 V2 V3)平均激活范围69个像素,平均T值9.8;左侧平均激活范围64个像素,平均T值9;二者缺乏明显统计学意义。②盲生盲点鉴别时在双侧视皮层有散在小的激活簇,右侧(V1 V2 V3)平均激活范围16个像素,平均T值4.1;左侧平均激活范围12个像素,平均T值3.8;盲文阅读激活范围与T值同盲点鉴别任务比较有显著性差别,P<0.001。③盲生在盲文阅读时还显示以左侧为优势的两侧BA4、BA3、BA7及SMA(补充运动区)、左侧额下回激活。④正常组除了以左侧为优势的两侧BA4、BA3、左侧BA7及BA6激活外,视觉皮层没有激活。结论早期视觉剥夺盲人阅读盲文时视觉皮层激活,视觉皮层功能发生了重组,具有参与处理复杂文字语言的高级认知功能。     

Cortical lateralization during verb generation: a combined ERP and fMRI study

Lateralization of scalp-recorded event-related potentials (ERPs) and functional MRI (fMRI) activation was investigated using a verb generation task in 10 healthy right-handed adults. ERPs showed an early transient positivity in the left inferior temporal region (500-1250 ms) following auditory presentation of the stimulus noun. A sustained slow cortical negativity of later onset (1250-3000 ms) was then recorded, most pronounced over left inferior frontal regions. fMRI data were in agreement with both ERP effects, showing left lateralized activation in inferior and superior temporal as well as inferior frontal cortices. Lateralized ERP effects occurred during the verb generation task but not during passive word listening or during word- and nonword repetition. Thus, ERPs and fMRI provided convergent evidence regarding language lateralization, with ERPs revealing the temporal sequence of posterior to anterior cortical activation during semantic retrieval.     

Callosal tracts and patterns of hemispheric dominance: a combined fMRI and DTI study

Left-hemispheric dominance for language and right-hemispheric dominance for spatial processing are distinctive characteristics of the human brain. However, variations of these hemispheric asymmetries have been observed, with a minority showing crowding of both functions to the same hemisphere or even a mirror reversal of the typical lateralization pattern. Here, we used diffusion tensor imaging and functional magnetic imaging to investigate the role of the corpus callosum in participants with atypical hemispheric dominance. The corpus callosum was segmented according to the projection site of the underlying fibre tracts. Analyses of the microstructure of the identified callosal segments revealed that atypical hemispheric dominance for language was associated with high anisotropic diffusion through the corpus callosum as a whole. This effect was most evident in participants with crowding of both functions to the right. The enhanced anisotropic diffusion in atypical hemispheric dominance implies that in these individuals the two hemispheres are more heavily interconnected.     

Attentional systems in target and distractor processing: a combined ERP and fMRI study

The interplay of "top-down" and "bottom-up" regulated mechanisms is of particular relevance for the rapid (re-)focusing of attention to environmental changes. The purpose of the study was to explore the differential contributions of frontoparietal attentional networks involved in top-down and stimulus-driven processing to the detection of "target" and "distractor" events in a visual three-stimulus oddball paradigm. Thirteen healthy subjects underwent separate event-related potential (ERP) and whole-brain functional magnetic resonance imaging (fMRI) measurements during the oddball task. The targets, which were difficult to detect, elicited a classical posterior P3b whereas the distractor stimuli were followed by a centro-frontal P3a ERP. The fMRI data showed activation of the temporoparietal junction (TPJ) bilaterally and right prefrontal cortex associated with both the target and distractor conditions. This network has previously been described as an attentional system that is predominantly stimulus driven and that responds to rare events. Furthermore, target processing produced bilateral perisylvian activity, which has been related to the "retrieval mode". Processing of the distractors activated the frontal eye fields (FEFs) and bilateral superior parietal cortex, areas engaged in attention switching and voluntary allocation of attention. Additional left prefrontal activation suggested an involvement of the cortical system for working memory encoding. Our results thus demonstrate that distractor and target processing engage a common neuronal system for the detection of rare events, but also task-specific subsystems related to attention and memory processes.     

Neural basis of phonological processing in second language reading: an fMRI study of Chinese regularity effect

The present study examined the neural basis of phonological processing in Chinese later acquired as a second language (L2). The regularity effect of Chinese was selected to elucidate the addressed phonological processing. We recruited a group of alphabetic language speakers who had been learning Chinese as L2 for at least one year, and a control group of native Chinese speakers. Participants from both groups exhibited a regularity effect in a pilot behavioral test. Neuroimaging results revealed that L2 learners exhibited stronger activation than native Chinese speakers in the right occipitotemporal region (i.e. right lingual gyrus and right fusiform gyrus). Moreover, L2 learners exhibited greater activations in the ventral aspects of the left inferior parietal lobule (LIPL) and the left inferior frontal gyrus (LIFG) for irregular character reading minus regular character reading. In contrast, native Chinese speakers exhibited more dorsal activations in the LIPL and LIFG. According to the "accommodation/assimilation" hypothesis of second language reading, the current findings suggest that native speakers of alphabetic languages utilized an accommodation pattern for the specific requirements of the visual form of Chinese characters, and an assimilation pattern for orthography-to-phonology transformation in Chinese reading.     

Stimulus properties matter more than perspective: an fMRI study of mental imagery and silent reading of action phrases

The role of the primary motor cortex (M1) in tasks involving action words remains controversial. Therefore, we investigated whether the previously reported involvement of M1 in processing of action words results from the semantic representation of action words per se, or if M1 activation may actually depend on whether or not subjects (explicitly or automatically) adopt a strategy of simulating the movements. Subjects silently read short phrases describing a situation which either involved a motor scene or not (STIMULUS: motor, non-motor phrases) and performed a secondary task: either they were explicitly asked to imagine the situation or they performed letter detection preventing them from using a simulation strategy (TASK: imagery vs. letter detection). In addition, phrases were presented both in 1st and 3rd person singular (PERSPECTIVE: 1st vs. 3rd person). This allowed us to investigate the influence of the secondary tasks (letter detection versus explicit motor imagery) on the neural activity in M1 during the processing of motor and non-motor phrases. We found differential left M1 activity in the task by stimulus interaction with enhanced M1 activation for imagery in the presence of motor phrases (vs. non-motor phrases) compared to letter detection of motor vs. non-motor phrases. This M1-activity was not differentially modulated by perspective. Therefore, M1 activation previously found in experiments of silent reading of action words may have resulted from the subjects' strategy to mentally simulate the movements during the processing of action words.     

Source localization of sensory gating: a combined EEG and fMRI study in healthy volunteers

Reduced sensory gating appears to be among the core features in schizophrenia. The sources of sensory gating however are largely unknown. The aim of the current study was to identify these sources, with concurrent EEG and fMRI methodology. Twenty healthy male volunteers were tested with identical P50 suppression paradigms in two separate sessions: an EEG setting, and an EEG concurrent with fMRI setting. The stimuli in the P50 paradigm consisted of weak electrical stimulation of the left median nerve. The stimuli were presented in pairs with either 500 ms or 1000 ms interstimulus intervals (ISI). No difference was found between the EEG setting and the concurrent EEG and fMRI setting. P50 suppression was, in both settings, found only in the 500 ms trials, not in the 1000 ms trials. EEG-dipole modeling resulted in 4 sources located in the medial frontal gyrus, the insula, the hippocampus, and primary somatosensory cortex. These sources corresponded to significant fMRI clusters located in the medial frontal gyrus, the insula, the claustrum, and the hippocampus. Activity in the hippocampus and the claustrum was higher in the trials with suppression, suggesting that these brain areas are involved in the inhibitory processes of P50 suppression. The opposite was found for activity in the medial frontal gyrus and the insula, suggesting that these brain areas are involved in the generation of the P50 amplitude. To our knowledge, this is the first study demonstrating that P50 suppression can be reliably assessed inside an MRI scanner.     

Neural deficits in second language reading: fMRI evidence from Chinese children with English reading impairment

In alphabetic language systems, converging evidence indicates that developmental dyslexia represents a disorder of phonological processing both behaviorally and neurobiologically. However, it is still unknown whether, impaired phonological processing remains the core deficit of impaired English reading in individuals with English as their second language and how it is represented in the neural cortex. Using functional magnetic resonance imaging, the present study investigated the neural responses to letter rhyming judgment (phonological task) and letter same/different judgment (orthographic task) in Chinese school children with English and Chinese reading impairment compared to typically developing children. Whole brain analyses with multiple comparison correction revealed reduced activation within the left lingual/calcarine gyrus during orthographic processing in children with reading impairment compared to typical readers. An independent region of interest analysis showed reduced activation in occipitotemporal regions during orthographic processing, and reduced activation in parietotemporal regions during phonological processing, consistent with previous studies in English native speakers. These results suggest that similar neural deficits are involved for impaired phonological processing in English as both the first and the second language acquired. These findings pose implications for reading remediation, educational curriculum design, and educational policy for second language learners.     

Maturation of luminance- and motion-defined form perception beyond adolescence: a combined ERP and fMRI study

Abilities to discriminate forms defined by motion continue to develop throughout childhood. To investigate late development of the visual motion system, we measured brain activity with event-related EEG potentials (ERPs) and functional magnetic resonance imaging (fMRI) in groups of adolescents (15-17 years) and adults (20-30 years) during a visual form discrimination task--with forms being either defined by motion or luminance contrast. We further explored whether possible developmental changes varied with the degree of motion coherence reflecting maturation specific to global motion processing. Both the fMRI activation patterns and ERP topographies were very similar between adolescents and adults, suggesting that the basic visual networks for processing motion and form are established by the age of 15-17. The ERP response to luminance- and motion-defined forms was dominated by a posterior negativity (N1: 120-270 ms). The N1 of the motion contrast was delayed in adolescents, whereas the N1 of the static condition did not differ between groups. Since the motion-evoked N1 is thought to arise in the middle temporal area MT/V5, our results indicate that visual motion processing in MT continues to get faster, becoming still more efficient during late development. Neither the ERP nor the fMRI results revealed maturation effects specific to motion coherence. This indicates that the specific mechanisms to process global dot motion are already mature in adolescence. The present findings support the view that static perception matures earlier than dynamic perception, and that these visual systems have different developmental courses.     

电刺激的fMRI的初步研究

目的研究不同频率的电刺激在大脑产生的激活,为理解和发展电刺激治疗疾病的方法提供依据和方向.方法对健康被试者的手腕和肘部内侧进行不同频率的低频电刺激,采用功能磁共振仪进行脑部激活图像的采集.结果表明不同频率的电刺激在大脑中的激活具有差异性,引起了运动皮层和躯体感觉区的明显激活.结论提示不同频率的电刺激可能激活了不同的神经通路,这些神经通路可能服务于中枢神经系统的不同功能,对于在电刺激的康复治疗中,选择恰当的刺激频率有一定的指导意义.     

A developmental fMRI study of the Stroop color-word task

We used fMRI to investigate developmental changes in brain activation during a Stroop color-word interference task. A positive correlation was observed between age and Stroop-related activation (n = 30) in the left lateral prefrontal cortex, the left anterior cingulate, and the left parietal and parieto-occipital cortices. No regions showed a negative correlation between activation and age. We further investigated age-related differences by stratifying the sample into three age groups: children (ages 7-11), adolescents (ages 12-16), and young adults (ages 18-22). Young adult subjects (n = 11) displayed significant activation in the inferior and middle frontal gyri bilaterally, the left anterior cingulate, and bilateral inferior and superior parietal lobules. Between-group comparisons revealed that young adults had significantly greater activation than adolescent subjects (n = 11) in the left middle frontal gyrus and that young adults showed significantly greater activation than children (n = 8) in the anterior cingulate and left parietal and parieto-occipital regions, as well as in the left middle frontal gyrus. Compared to children, both adult and adolescent subjects exhibited significantly greater activation in the parietal cortex. Adult and adolescent groups, however, did not differ in activation for this region. Together, these data suggest that Stroop task-related functional development of the parietal lobe occurs by adolescence. In contrast, prefrontal cortex function contributing to the Stroop interference task continues to develop into adulthood. This neuromaturational process may depend on increased ability to recruit focal neural resources with age. Findings from this study, the first developmental fMRI investigation of the Stroop interference task, provide a template with which normal development and neurodevelopmental disorders of prefrontal cortex function can be assessed.     

Cortico-striatal connectivity and cognition in normal aging: a combined DTI and resting state fMRI study

Resting state fMRI studies have found that cognitive decline in aging is associated with alterations in functional connectivity of distributed neural systems in the brain. While functional connections have been shown to rely on the underlying structural connectivity, direct structural connections have been studied in only a few distributed cortical systems so far. It is well known that subcortical nuclei have structural connections to the entire cortex. We hypothesized that structural subcortico-cortical connections may provide integral routes for communication between cortical resting state networks, and that changes in the integrity of these connections have a role in cognitive aging. We combined anatomical MRI, diffusion tensor MRI, and resting state fMRI in 100 healthy elderly to identify fiber bundles connecting cortical resting state networks to subcortical nuclei. In identified tracts, white matter fiber bundle integrity measures were compared to composite cognitive measures on executive function, processing speed, and memory performance. The integrity (FA values) in selected fiber bundles correlated strongly with cognitive measures on executive function and processing speed. Correlation was most pronounced between executive function and fiber bundles connecting the putamen to the dorsal attention network (r=0.73, p<0.001). Our findings show that unique cortico-subcortical fiber bundles can be identified for a range of cortical resting state networks, and indicate that these connections play an important role in cortical resting state network communication and cognition.     

对中国学生英语阅读能力的研究--提高医学护理专业学生的阅读能力

英语学习中的4个基本技能:听、说、读、写,在很多文章中都被探讨过。对于阅读能力,以往的文章大多讨论的是语言习得中阅读行为的最终结果。而阅读行为的重要组成部分—阅读过程往往被忽略。本文试图从学习者阅读的心理过程出发,分析读者在阅读过程中的思维模式,从而提出一些在第二语言习得中有助于提高学生阅读能力的有效途径。