Alexia with agraphia due to the left posterior inferior temporal lobe lesion--neuropsychological analysis and its pathogenetic mechanisms

We report three cases of alexia with agraphia due to the left posterior inferior temporal lesions. In Case 1, the reading disability was more prominent in the use of Kana than in the use of Kanji, which is similar to previously reported cases of alexia with agraphia due to angular gyrus lesion. In Cases 2 and 3, by contrast, the reading disability was more prominent in the use of Kanji than in the use of Kana. In spontaneous writing and dictation, the disability was more pronounced in the use of Kanji compared with the use of Kana. In each of the three cases, the CT scan and positron emission tomography showed a localized lesion in the lower part of the left posterior temporal lobe. A typical form of an alexia with agraphia could be caused not only by the left angular lesion but also by the left posterior inferior temporal lesion. We discuss the neuropsychological analysis and pathogenetic mechanisms of alexia with agraphia due to the left posterior inferior temporal lesion in the comparison of alexia with agraphia caused by the left angular lesion.     

Neural correlates of lexical and sublexical processes in reading

The purpose of the present study was to compare the brain regions and systems that subserve lexical and sublexical processes in reading. In order to do so, three types of tasks were used: (i). silent reading of very high frequency regular words (lexical task); (ii). silent reading of nonwords (sublexical task); and, (iii). silent reading of very low frequency regular words (sublexical task). All three conditions were contrasted with a visual/phonological baseline condition. The lexical condition engaged primarily an area at the border of the left angular and supramarginal gyri. Activation found in this region suggests that this area may be involved in mapping orthographic-to-phonological whole word representations. Both sublexical conditions elicited significantly greater activation in the left inferior prefrontal gyrus. This region is thought to be associated with sublexical processes in reading such as grapheme-to-phoneme conversion, phoneme assembly and underlying verbal working memory processes. Activation in the left IFG was also associated with left superior and middle temporal activation. These areas are thought to be functionally correlated with the left IFG and to contribute to a phonologically based form of reading. The results as a whole demonstrate that lexical and sublexical processes in reading activate different regions within a complex network of brain structures.     

Developmental changes in the linguistic brain after puberty

The development of reading skills is a complex and very long-lasting process. In an influential study Booth et al. demonstrated age-related changes in the activation of a network of left hemisphere regions, including the inferior frontal area, the superior temporal gyrus, and the angular gyrus. Interestingly, they found that the angular gyrus, which is involved in the mapping between phonological and orthographic representation, is automatically activated in adults during visual orthographic tasks not requiring this operation.     

A functional lesion in developmental dyslexia: left angular gyral blood flow predicts severity.

Functional imaging studies have shown reduced regional cerebral blood flow (rCBF) in temporal and inferior parietal regions in dyslexia. To relate such abnormalities to the severity of dyslexia, correlations between reading skill and rCBF during a series of reading tasks and visual fixation were mapped for 17 right-handed dyslexic men, ages 18-40, and 14 matched controls. These correlations uniquely identified the left angular gyrus as the most probable site of a functional lesion in dyslexia: Here, higher rCBF was associated with better reading skill in controls (p <.01), but with worse reading skill in dyslexia (p <.01). This suggests that greater reliance on this region normally facilitates reading, but impairs reading in dyslexia. Thus, developmental dyslexia may share a common localization with alexia.     

Phonological alexia with optic and tactile anomia: a neuropsychological and anatomical study

We describe a patient with phonological alexia caused by a small hemorrhage in the posterior-inferior portion of the left temporal lobe. The lesion induced a highly selective impairment of phonological reading without concomitant oral language deficits other than anomia for objects presented in the visual and tactile modalities. We propose that an intact dorsal pathway from inferior visual association areas to Wernicke's area via the angular gyrus could mediate reading by the lexical route, while damage to a ventral pathway disrupted the patient's ability to read nonwords. We suggest further that although visually and tactually presented objects could be recognized and both verbally and nonverbally identified, they could not be named because of a disconnection from the area of word representations.     

Neuroanatomical correlates of oral reading in acute left hemispheric stroke

Oral reading is a complex skill involving the interaction of orthographic, phonological, and semantic processes. Functional imaging studies with nonimpaired adult readers have identified a widely distributed network of frontal, inferior parietal, posterior temporal, and occipital brain regions involved in the task. However, while functional imaging can identify cortical regions engaged in the process under examination, it cannot identify those brain regions essential for the task. The current study aimed to identify those neuroanatomical regions critical for successful oral reading by examining the relationship between word and nonword oral reading deficits and areas of tissue dysfunction in acute stroke. We evaluated 91 patients with left hemisphere ischemic stroke with a test of oral word and nonword reading, and magnetic resonance diffusion-weighted and perfusion-weighted imaging, within 24-48 h of stroke onset. A voxel-wise statistical map showed that impairments in word and nonword reading were associated with a distributed network of brain regions, including the inferior and middle frontal gyri, the middle temporal gyrus, the supramarginal and angular gyri, and the middle occipital gyrus. In addition, lesions associated with word deficits were found to be distributed more frontally, while nonword deficits were associated with lesions distributed more posteriorly.     

Behavioral and fMRI evidence that cognitive ability modulates the effect of semantic context on speech intelligibility

Text cues facilitate the perception of spoken sentences to which they are semantically related (Zekveld, Rudner, et al., 2011). In this study, semantically related and unrelated cues preceding sentences evoked more activation in middle temporal gyrus (MTG) and inferior frontal gyrus (IFG) than nonword cues, regardless of acoustic quality (speech in noise or speech in quiet). Larger verbal working memory (WM) capacity (reading span) was associated with greater intelligibility benefit obtained from related cues, with less speech-related activation in the left superior temporal gyrus and left anterior IFG, and with more activation in right medial frontal cortex for related versus unrelated cues. Better ability to comprehend masked text was associated with greater ability to disregard unrelated cues, and with more activation in left angular gyrus (AG). We conclude that individual differences in cognitive abilities are related to activation in a speech-sensitive network including left MTG, IFG and AG during cued speech perception.     

Residual differences in language processing in compensated dyslexics revealed in simple word reading tasks

Using regional cerebral blood flow as an index of cerebral activity we studied dyslexic and control subjects during simple word reading tasks. The groups were pre-tested for reading skill and the dyslexic group had a lower reading performance but could read and comprehend standard texts. The aim was to elucidate differences in the cerebral activation pattern during reading. The tasks were simple enough that performance differences between the groups could be excluded. We found specific differences between the two groups that were dependent on the language task. When the visual route for language information was used, minor qualitative differences were found between the groups pertaining to the dominant hemisphere. Increasing the complexity of the task by using pseudowords activated the left frontal region more in the dyslexic group than in the control group. A similar effect was seen in a minor region in extrastriate lateral occipital cortex (BA 19). This finding indicates that the dyslexics used areas in these regions that the controls did not. On the other hand, the dyslexics activated less in the right angular gyrus, right dorsolateral prefrontal cortex, and in the right pallidum. Reading skill correlated with the level of activity in the right frontal cortex. We conclude, that cerebral activation pattern elicited by reading is different in dyslexics compared to controls in spite of an almost complete functional compensation.     

Brain activation on pre-reading tasks reveals at-risk status for dyslexia in 6-year-old children

In this fMRI-study, 6-year-old children considered at risk for dyslexia were compared with an age-/gender-matched control group for differences in brain activation when presented with visual stimuli differing in demands for literacy processing. Stimuli were nameable pictures, brand logos familiar to children, and written words - these were either regularly spelled using early-acquired rules ("alphabetic") or more complex ("orthographic"). Brain responses distinguished between the presentation conditions, as a function of group, within many cortical areas. Activation in the alphabetic and orthographic conditions in the left angular gyrus correlated with individual at-risk index scores, and activation in inferior occipito-temporal regions further indicated differential activation for the two groups related to orthographic processing, especially. Since similar patterns are reported in adult dyslexics when processing written words, it appears that sensitivity to the cortical differentiation of reading networks is established prior to formal literacy training.     

Neural substrates of impaired categorical perception of phonemes in adult dyslexics: an fMRI study

Phonological developmental dyslexics remain impaired in phonetic categorical perception (CP) even in adulthood. We studied the brain correlates of CP in dyslexics and controls using a block design fMRI protocol and stimuli from an phonetic continuum between natural /Pa/ and /Ta/ syllables. Subjects performed a pseudo-passive listening task which does not imply voluntary categorical judgment. In the control group, categorical deviant stimuli elicited specific activations in the left angular gyrus, the right inferior frontal gyrus and the right superior cingulate cortex. These regions were not activated in the dyslexic group in which activation was observed for acoustic but not phonetic changes in stimuli. Failures to activate key regions for language perception and auditory attention in dyslexic might account for persistent deficits in phonological awareness and reading tasks.     

词间空格促进从右向左呈现汉语文本的阅读

摘要：为探讨在无阅读经验时,词切分线索是否促进读者的阅读与词汇识别,本研究操纵了阅读方向、词切分线索与目标词的词频。采用眼动仪记录读者的阅读过程。结果发现：阅读方向与词切分线索的交互作用显著,词切分显著地促进了从右向左呈现文本的阅读,但并不影响阅读从左向右呈现的文本;词切分条件下目标词的注视时间显著地短于无词切分条件。表明词切分线索促进了无阅读经验时的阅读,支持词切分线索的促进与文本不熟悉干扰之间权衡作用的假设。     

Direction counts: a comparative study of spatially directional counting biases in cultures with different reading directions

Western adults associate small numbers with left space and large numbers with right space. Where does this pervasive spatial–numerical association come from? In this study, we first recorded directional counting preferences in adults with different reading experiences (left to right, right to left, mixed, and illiterate) and observed a clear relationship between reading and counting directions. We then recorded directional counting preferences in preschoolers and elementary school children from three of these reading cultures (left to right, right to left, and mixed). Culture-specific counting biases existed before reading acquisition in children as young as 3 years and were subsequently modified by early reading experience. Together, our results suggest that both directional counting and scanning activities contribute to number–space associations.     

Effective brain connectivity in children with reading difficulties during phonological processing

Using Dynamic Causal Modeling (DCM) and functional magnetic resonance imaging (fMRI), we examined effective connectivity between three left hemisphere brain regions (inferior frontal gyrus, inferior parietal lobule, fusiform gyrus) and bilateral medial frontal gyrus in 12 children with reading difficulties (M age=12.4, range: 8.11-14.10) and 12 control children (M age=12.3, range: 8.9-14.11) during rhyming judgments to visually presented words. More difficult conflicting trials either had similar orthography but different phonology (e.g. pint-mint) or similar phonology but different orthography (e.g. jazz-has). Easier non-conflicting trials had similar orthography and phonology (e.g. dime-lime) or different orthography and phonology (e.g. staff-gain). The modulatory effect from left fusiform gyrus to left inferior parietal lobule was stronger in controls than in children with reading difficulties only for conflicting trials. Modulatory effects from left fusiform gyrus and left inferior parietal lobule to left inferior frontal gyrus were stronger for conflicting trials than for non-conflicting trials only in control children but not in children with reading difficulties. Modulatory effects from left inferior frontal gyrus to inferior parietal lobule, from medial frontal gyrus to left inferior parietal lobule, and from left inferior parietal lobule to medial frontal gyrus were positively correlated with reading skill only in control children. These findings suggest that children with reading difficulties have deficits in integrating orthography and phonology utilizing left inferior parietal lobule, and in engaging phonological rehearsal/segmentation utilizing left inferior frontal gyrus possibly through the indirect pathway connecting posterior to anterior language processing regions, especially when the orthographic and phonological information is conflicting.     

How does reading direction modulate perceptual asymmetry effects?

Left-side bias effects refer to a bias towards the left side of the stimulus/space in perceptual/visuospatial judgments, and are argued to reflect dominance of right hemisphere processing. It remains unclear whether reading direction can also account for the bias effect. Previous studies comparing readers of languages read from left to right with those read from right to left (e.g., French vs. Hebrew) have obtained inconsistent results. As a language that can be read from left to right or from right to left, Chinese provides a unique opportunity for a within-culture examination of reading direction effects. Chinese participants performed a perceptual judgment task (with both face and Chinese character stimuli; Experiment 1) and two visuospatial attention tasks (the greyscales and line bisection tasks; Experiment 2) once before and once after a reading task, in which they read Chinese passages either from left to right or from right to left for about 20 min. After reading from right to left, participants showed significantly reduced left-side bias in Chinese character perceptual judgments but not in the other three tasks. This effect suggests that the role of reading direction on different forms of left-side bias may differ, and its modulation may be stimulus-specific.     

Early development of letter specialization in left fusiform is associated with better word reading and smaller fusiform face area

A functional region of left fusiform gyrus termed “the visual word form area” (VWFA) develops during reading acquisition to respond more strongly to printed words than to other visual stimuli. Here, we examined responses to letters among 5‐ and 6‐year‐old early kindergarten children (N = 48) with little or no school‐based reading instruction who varied in their reading ability. We used functional magnetic resonance imaging (fMRI) to measure responses to individual letters, false fonts, and faces in left and right fusiform gyri. We then evaluated whether signal change and size (spatial extent) of letter‐sensitive cortex (greater activation for letters versus faces) and letter‐specific cortex (greater activation for letters versus false fonts) in these regions related to (a) standardized measures of word‐reading ability and (b) signal change and size of face‐sensitive cortex (fusiform face area or FFA; greater activation for faces versus letters). Greater letter specificity, but not letter sensitivity, in left fusiform gyrus correlated positively with word reading scores. Across children, in the left fusiform gyrus, greater size of letter‐sensitive cortex correlated with lesser size of FFA. These findings are the first to suggest that in beginning readers, development of letter responsivity in left fusiform cortex is associated with both better reading ability and also a reduction of the size of left FFA that may result in right‐hemisphere dominance for face perception.     

No strong evidence for lateralisation of word reading and face recognition deficits following posterior brain injury

Face recognition and word reading are thought to be mediated by relatively independent cognitive systems lateralised to the right and left hemispheres, respectively. In this case, we should expect a higher incidence of face recognition problems in patients with right hemisphere injury and a higher incidence of reading problems in patients with left hemisphere injury. We tested this hypothesis in a group of 31 patients with unilateral right or left hemisphere infarcts in the territory of the posterior cerebral arteries. In most domains tested (e.g., visual attention, object recognition, visuo-construction, motion perception), we found that both patient groups performed significantly worse than a matched control group. In particular, we found a significant number of face recognition deficits in patients with left hemisphere injury and a significant number of patients with word reading deficits following right hemisphere injury. This suggests that face recognition and word reading may be mediated by more bilaterally distributed neural systems than is commonly assumed.     

Binocular foveation in reading

We present a theory of foveation in normal binocular reading. We consider the pervasive, nontrivial binocular fixation disparities (FDs) observed in reading and relate them to the computational problem of resolving retinal disparities in depth perception. We infer that the right eye's fixation being to the right of the left eye's in reading promotes binocular fusion in challenging conditions. We then show a different (nonfusional) processing advantage for the right eye's fixation being to the left of the left eye's in reading conditions in which binocular fusion is assured, by modeling the combined influence of foveal splitting, contralateral preference, ocular prevalence, and fixation disparity. This synthesis of anatomically grounded research in different aspects of visual processing produces a theory of foveation in reading that matches current data and makes testable predictions.     

Hemisphere differences in conscious and unconscious word reading

Hemisphere differences in word reading were examined using explicit and implicit processing measures. In an inclusion task, which indexes both conscious (explicit) and unconscious (implicit) word reading processes, participants were briefly presented with a word in either the right or the left visual field and were asked to use this word to complete a three-letter word stem. In an exclusion task, which estimates unconscious word reading, participants completed the word stem with any word other than the prime word. Experiment 1 showed that words presented to either visual field were processed in very similar ways in both tasks, with the exception that words in the right visual field (left hemisphere) were more readily accessible for conscious report. Experiment 2 indicated that unconsciously processed words are shared between the hemispheres, as similar results were obtained when either the same or the opposite visual field received the word stem. Experiment 3 demonstrated that this sharing between hemispheres is cortically mediated by testing a split-brain patient. These results suggest that the left hemisphere advantage for word reading holds only for explicit measures; unconscious word reading is much more balanced between the hemispheres.     

认知过程中大脑两半球的协同活动——若干实验结果的分析和再分析

本文对以往裂脑患者、右半球摘除患者和正常被试的若干实验结果进行了综合性的二次分析;同时对双脑协同活动的机制进行了讨论。依据实验资料提出双脑协同话动的两种可能的模式:〈1〉双脑互补模式;〈2〉双脑互扰模式。 统览以往文献,觉得把实验数据的算术平均数或某些概率运算的结果作为大脑一侧优势的指标可能是欠妥当的,因为它忽略了数据本身的性质。依据从三种视野所分别获得的数据可能具有向量性质,故建议: 〈1〉用左、右视野所获数据的向量差作为双脑协同活动中协同程度或协同水平的指标; 〈2〉把三组数据放在平面直角坐标系中分析,把左、右视野数据与中问视野数据之间的夹角差数作为单侧视野相对认知优势的指标。