Acquired dyslexias following temporal lesions.

The acquisition of reading by children is supported by deep changes in the brain systems devoted to vision and language. The left temporal lobe contributes critically to both systems, and lesions affecting it may therefore cause both peripheral vision-related and central language-related reading impairments. The diversity of peripheral dyslexias reflects the anatomical and functional division of the visual cortex into early visual regions, whose lesions have a limited impact on reading; ventral regions, whose lesions are mostly associated to Pure Alexia; and dorsal regions, whose lesions may yield spatial, neglect-related, and attentional dyslexias. Similarly, central alexias reflect the broad distinction, within language processes, between phonological and lexico-semantic components. Phonological and surface dyslexias roughly result from impairment of the former and the latter processes, respectively, while deep dyslexia may be seen as the association of both. In this chapter, we review such types of acquired dyslexias, their clinical features, pathophysiology, and anatomical correlates.

Phonological and surface dyslexia in individuals with brain tumors: Performance pre-, intra-, immediately post-surgery and at follow-up.

We address existing controversies regarding neuroanatomical substrates of reading-aloud processes according to the dual-route processing models, in this particular instance in a series of 49 individuals with brain tumors who performed several reading tasks of real-time neuropsychological testing during surgery (low- to high-grade cerebral neoplasms involving the left hemisphere). We explored how reading abilities in individuals with brain tumors evolve during and after surgery for a brain tumor, and we studied the reading performance in a sample of 33 individuals in a 4-month follow-up after surgery. Impaired reading performance was seen pre-surgery in 7 individuals with brain tumors, intra-surgery in 18 individuals, at immediate post-surgery testing in 26 individuals, and at follow-up in 5 individuals. We classified their reading disorders according to operational criteria for either phonological or surface dyslexia. Neuroimaging results are discussed within the theoretical framework of the dual-route model of reading. Lesion-mask subtraction analyses revealed that areas selectively related with phonological dyslexia were located-along with the left hemisphere dorsal stream-in the Rolandic operculum, the inferior frontal gyrus, the precentral gyrus, the supramarginal gyrus, the insula (and/or the underlying external capsule), and parts of the superior longitudinal fasciculus, whereas lesions related to surface dyslexia involved the ventral stream, that is, the left middle and inferior temporal gyrus and parts of the left inferior longitudinal fasciculus.

Alexia and agraphia in Spanish.

BACKGROUND: Every language has certain specific idiosyncrasies in its writing system. Cross-linguistic analyses of alexias and agraphias are fundamental to understand commonalities and differences in the brain organization of written language. Few reports of alexias and agraphias in the Spanish language are currently available. AIMS: To analyse the clinical manifestations of alexias and agraphias in Spanish, and the effect of demographic variables. METHODS & PROCEDURES: Spanish versions of the Western Aphasia Battery (WAB) and Boston Diagnostic Aphasia Examination (BDAE) were used for language assessment. Lesion localization was obtained by using computed axial tomography and magnetic resonance imaging. The final sample included 200 patients: 195 (97.5%) right-handed and five (2.5%) left-handed; 119 men and 81 women with a mean age of 57.37 years (SD = 15.56), education of 13.52 years (SD = 4.08), and mean time post-onset of 6.58 months (SD = 12.94). Using the WAB, four quotients were calculated: aphasia quotient (AQ), reading-writing quotient (RWQ), language quotient (LQ) and cortical quotient (CQ). OUTCOMES & RESULTS: The types of aphasia were: global = 11 patients (5.5%), Broca = 31 (15.5%), Wernicke = 30 (15.0%), conduction = 22 (11.0%), transcortical sensory = 17 (8.5%), transcortical motor = 3 (1.5%), amnesic or anomic = 54 (27.0%) and mixed non-fluent = 32 (16.0%). The degree of oral and written language impairment differed across the various aphasia types. Most severe reading and writing difficulties were found in global, mixed non-fluent and transcortical motor aphasia; fewer difficulties were observed in amnesic, Broca and conduction aphasia. The severity of the written language impairments paralleled the severity of the oral language disturbances. Age negatively, while schooling positively, correlated with the scores in reading and writing tests. No effect of sex and time since onset was found. CONCLUSIONS & IMPLICATIONS: In Spanish-speaking aphasia patients, difficulties in reading and writing are similar to oral language difficulties. This similarity of performance is mostly based on severity rather than the participants' patterns of errors. What this paper adds What is already known on the subject There is limited information about alexia and agraphia in Spanish. What this paper adds to existing knowledge An extensive study with a large sample of patients. What are the potential or actual clinical implications of this work? The study contributes to the clinical management of patients with reading and writing disturbances.

Selective impairment of On-reading (Chinese-style pronunciation) in alexia with agraphia for kanji due to subcortical hemorrhage in the left posterior middle temporal gyrus.

We report a patient with alexia with agraphia for kanji after hemorrhage in the left posterior middle temporal gyrus. The results of single-character kanji reading and two-character on- (Chinese-style pronunciation), kun- (native Japanese pronunciation), and Jukujikun (irregular kun-) reading word tests revealed that the patient could not read kanji characters with on-reading but read the characters with kun-reading. We consider that this on-reading alexia was caused by disconnection between the posterior inferior temporal cortex (orthographic lexicon) and the posterior superior temporal gyrus (phonological lexicon), and preserved kun- and Jukujikun-reading was realized by bypassing the orthography-to-phonology route by the semantic route.

Surface errors without semantic impairment in acquired dyslexia: a voxel-based lesion-symptom mapping study.

Patients with surface dyslexia have disproportionate difficulty pronouncing irregularly spelled words (e.g. pint), suggesting impaired use of lexical-semantic information to mediate phonological retrieval. Patients with this deficit also make characteristic 'regularization' errors, in which an irregularly spelled word is mispronounced by incorrect application of regular spelling-sound correspondences (e.g. reading plaid as 'played'), indicating over-reliance on sublexical grapheme-phoneme correspondences. We examined the neuroanatomical correlates of this specific error type in 45 patients with left hemisphere chronic stroke. Voxel-based lesion-symptom mapping showed a strong positive relationship between the rate of regularization errors and damage to the posterior half of the left middle temporal gyrus. Semantic deficits on tests of single-word comprehension were generally mild, and these deficits were not correlated with the rate of regularization errors. Furthermore, the deep occipital-temporal white matter locus associated with these mild semantic deficits was distinct from the lesion site associated with regularization errors. Thus, in contrast to patients with surface dyslexia and semantic impairment from anterior temporal lobe degeneration, surface errors in our patients were not related to a semantic deficit. We propose that these patients have an inability to link intact semantic representations with phonological representations. The data provide novel evidence for a post-semantic mechanism mediating the production of surface errors, and suggest that the posterior middle temporal gyrus may compute an intermediate representation linking semantics with phonology.

The anatomical foundations of acquired reading disorders: a neuropsychological verification of the dual-route model of reading.

In this study we investigated the neural correlates of acquired reading disorders through an anatomo-correlative procedure of the lesions of 59 focal brain damaged patients suffering from acquired surface, phonological, deep, undifferentiated dyslexia and pure alexia. Two reading tasks, one of words and nonwords and one of words with unpredictable stress position, were used for this study. We found that surface dyslexia was predominantly associated with left temporal lesions, while in phonological dyslexia the lesions overlapped in the left insula and the left inferior frontal gyrus (pars opercularis) and that pure alexia was associated with lesions in the left fusiform gyrus. A number of areas and white matter tracts, which seemed to involve processing along both the lexical and the sublexical routes, were identified for undifferentiated dyslexia. Two cases of deep dyslexia with relatively dissimilar anatomical correlates were studied, one compatible with Coltheart's right-hemisphere hypothesis (1980) whereas the other could be interpreted in the context of Morton and Patterson's (1980), multiply-damaged left-hemisphere hypothesis. In brief, the results of this study are only partially consistent with the current state of the art, and propose new and stimulating challenges; indeed, based on these results we suggest that different types of acquired dyslexia may ensue after different cortical damage, but white matter disconnection may play a crucial role in some cases.

Beyond the visual word form area: the orthography-semantics interface in spelling and reading.

Lexical orthographic information provides the basis for recovering the meanings of words in reading and for generating correct word spellings in writing. Research has provided evidence that an area of the left ventral temporal cortex, a subregion of what is often referred to as the visual word form area (VWFA), plays a significant role specifically in lexical orthographic processing. The current investigation goes beyond this previous work by examining the neurotopography of the interface of lexical orthography with semantics. We apply a novel lesion mapping approach with three individuals with acquired dysgraphia and dyslexia who suffered lesions to left ventral temporal cortex. To map cognitive processes to their neural substrates, this lesion mapping approach applies similar logical constraints to those used in cognitive neuropsychological research. Using this approach, this investigation: (a) identifies a region anterior to the VWFA that is important in the interface of orthographic information with semantics for reading and spelling; (b) determines that, within this orthography-semantics interface region (OSIR), access to orthography from semantics (spelling) is topographically distinct from access to semantics from orthography (reading); (c) provides evidence that, within this region, there is modality-specific access to and from lexical semantics for both spoken and written modalities, in both word production and comprehension. Overall, this study contributes to our understanding of the neural architecture at the lexical orthography-semantic-phonological interface within left ventral temporal cortex.

Prose reading in neglect.

Prose reading has been shown to be a very sensitive measure of Unilateral Spatial Neglect. However, little is known about the relationship between prose reading and other measures of neglect and its severity, or between prose reading and single word reading. Thirty participants with a first stroke in the right hemisphere and clear symptoms of spatial neglect in everyday life were assessed with tests of prose reading (text in one column book-like, and in two columns magazine-like), single words reading, and a battery of 13 tests investigating neglect. Seventy percent of these participants omitted words at the beginning of the text (left end), showing Prose Reading Neglect (PRN). The participants showing PRN differed from those not showing PRN only for the overall severity of neglect, and had a lesion centred on the insula, putamen and superior temporal gyrus. Double dissociations emerged between PRN and single word reading neglect, suggesting different cognitive requirements between the two tests: parallel processing in single word reading vs. serial analysis in text reading. Notably, the pattern of neglected text varied dramatically across participants presenting with PRN, including dissociations between reading performance of one and two columns text. Prose reading proved a complex and unique task which should be directly investigated to predict the effects of unilateral neglect. The outcome of this study should also inform clinical assessment and advises given to patients and care-givers.

Prelexical representations and processes in reading: evidence from acquired dyslexia.

We report a detailed and extensive single-case study of an acquired dyslexic patient, L.H.D., who suffered a left-hemisphere lesion as a result of a ruptured aneurysm. We present evidence that L.H.D.'s reading errors stem from a deficit in visual letter identification, and we use her deficit as a basis for exploring a variety of issues concerning prelexical representations and processes in reading. First, building on the work of other researchers, we present evidence that the prelexical reading system includes an allograph level of representation that represents each distinct visual shape of a letter (e.g., a, A, etc., for the letter A). We extend a theory proposed by Caramazza and Hillis [Caramazza, A., & Hillis, A. (1990a). Spatial representation of words in the brain implied by studies of a unilateral neglect patient. Nature, 346, 267-269] to include an allograph level, and we probe the nature of the allograph representations in some detail. Next, we explore the implications of visual similarity effects and letter perseverations in L.H.D.'s reading performance, arguing that these effects shed light on activation dynamics in the prelexical reading system and on the genesis of L.H.D.'s errors. We also probe the processing of letter case in the visual letter identification process, proposing that separate abstract letter identity and case representations are computed. Finally, we present evidence that the allograph level as well as the abstract letter identity level implement a word-based frame of reference.

Representation of letter position in single-word reading: evidence from acquired dyslexia.

Visual word recognition requires information about the positions as well as the identities of the letters in a word. This study addresses representation of letter position at prelexical levels of the word recognition process. We present evidence from an acquired dyslexic patient, L.H.D., who perseverates letters in single-word reading tasks: Far more often than expected by chance, L.H.D.'s reading responses include letters from preceding responses (e.g., SAILOR read as SAILOG immediately after FLAG was read correctly). Analyses carried out over two large data sets compared the positions of perseverated letters (e.g., the G in SAILOG) with the positions of the corresponding "source" letters (e.g., the G in FLAG). The analyses assessed the extent to which the perseverations preserved source position as defined by various theories of letter position representation. The results provided strong evidence for graded both-edges position representations, in which the position of each letter is encoded coarsely relative to both the beginning and the end of the word. Alternative position representation schemes, including letter-context and orthosyllabic schemes, were not supported.

Distinct patterns of brain function in children with isolated spelling impairment: new insights.

Studies investigating reading and spelling difficulties heavily focused on the neural correlates of reading impairments, whereas spelling impairments have been largely neglected so far. Hence, the aim of the present study was to investigate brain structure and function of children with isolated spelling difficulties. Therefore, 31 children, aged ten to 15 years, were investigated by means of functional MRI and DTI. This study revealed that children with isolated spelling impairment exhibit a stronger right hemispheric activation compared to children with reading and spelling difficulties and controls, when engaged in an orthographic decision task, presumably reflecting a highly efficient serial grapheme-phoneme decoding compensation strategy. In addition, children with spelling impairment activated bilateral inferior and middle frontal gyri during processing correctly spelled words and misspelled words, whereas the other two groups showed bilateral activation only in the misspelled condition, suggesting that additional right frontal engagement could be related to generally higher task demand and effort. DTI analyses revealed stronger frontal white matter integrity (fractional anisotropy) in controls (compared to spelling and reading impaired children), whereas no structural differences between controls and spelling impaired children were observed.

The role of the left anterior temporal lobe in exception word reading: reconciling patient and neuroimaging findings.

Semantic dementia (SD) is a neurodegenerative disease that occurs following the atrophy of the anterior temporal lobes (ATLs). It is characterised by the degradation of semantic knowledge and difficulties in reading exception words (surface dyslexia). This disease has highlighted the role of the ATLs in the process of exception word reading. However, imaging studies in healthy subjects have failed to detect activation of the ATLs during exception word reading. The aim of the present study was to test whether the functional brain regions that mediate exception word reading in normal readers overlap those brain regions atrophied in SD. In Study One, we map the brain regions of grey matter atrophy in AF, a patient with mild SD and surface dyslexia profile. In Study Two, we map the activation pattern associated with exception word compared to pseudoword reading in young, healthy participants using fMRI. The results revealed areas of significant activation in healthy subjects engaged in the exception word reading task in the left anterior middle temporal gyrus, in a region observed to be atrophic in the patient AF. These results reconcile neuropsychological and functional imaging data, revealing the critical role of the left ATL in exception word reading.

The word-length effect in acquired alexia, and real and virtual hemianopia.

A word-length effect is often described in pure alexia, with reading time proportional to the number of letters in a word. Given the frequent association of right hemianopia with pure alexia, it is uncertain whether and how much of the word-length effect may be attributable to the hemifield loss. To isolate the contribution of the visual field defect, we simulated hemianopia in healthy subjects with a gaze-contingent paradigm during an eye-tracking experiment. We found a minimal word-length effect of 14 ms/letter for full-field viewing, which increased to 38 ms/letter in right hemianopia and to 31 ms/letter in left hemianopia. We found a correlation between mean reading time and the slope of the word-length effect in hemianopic conditions. The 95% upper prediction limits for the word-length effect were 51 ms/letter in subjects with full visual fields and 161 ms/letter with simulated right hemianopia. These limits, which can be considered diagnostic criteria for an alexic word-length effect, were consistent with the reading performance of six patients with diagnoses based independently on perimetric and imaging data: two patients with probable hemianopic dyslexia, and four with alexia and lesions of the left fusiform gyrus, two with and two without hemianopia. Two of these patients also showed reduction of the word-length effect over months, one with and one without a reading rehabilitation program. Our findings clarify the magnitude of the word-length effect that originates from hemianopia alone, and show that the criteria for a word-length effect indicative of alexia differ according to the degree of associated hemifield loss.

Covert reading of letters in a case of global alexia.

This study describes the case of a global alexic patient with a severe reading deficit affecting words, letters and Arabic numbers, following a left posterior lesion. The patient (VA) could not match spoken letters to their graphic form. A preserved ability to recognize shape and canonical orientation of letters indicates intact access to the representation of letters and numbers as visual objects. A relatively preserved ability to match lowercase to uppercase letters suggests partially spared access to abstract letter identities independently of their visual forms. The patient was also unable to match spoken letters and numbers to their visual form, indicating that she could not access the graphemic representations of letters from their phonological representations. This pattern of performance suggests that the link between graphemic and phonological representations is disrupted in this patient. We hypothesize that VA' residual reading abilities are supported by the right hemisphere.

Reading disorders and weak Verbal IQ following left hemisphere stroke in children: no evidence of compensation.

Children who suffer a left-hemisphere (LH) stroke do not appear to experience the verbal deficits that are apparent in adults with similar lesions. To explain these findings it has been suggested that the plasticity of the developing brain enables homologous areas in the right hemisphere (RH) to compensate for LH weakness. In this paper we find evidence against this theory from investigations into the effect of LH and RH lesions on intelligence and literacy skills in a group of children with unilateral postnatal stroke. At group level, there was no significant effect of LH stroke on Verbal IQ (VIQ) or upon reading ability, when compared with RH stroke. But at the individual level, the majority of children with LH stroke achieved standard scores below average, with some below -2 SD. The standard scores of children with RH lesions were normally distributed, showing no detrimental effect that would indicate compensation. Large discrepancies between VIQ and Performance IQ (PIQ), in both directions, were also a characteristic of the LH group. Using normative data that we collected on the reading of irregular and regular words and nonwords, we identified patterns of phonological and surface dyslexia in both lesioned groups. We argue that LH stroke reduces the efficiency of verbally-related skills, but that the processes available to children with postnatal lesions are those available to normally developing children, and that these can entail processes in either hemisphere.

The relationship between visual crowding and letter confusability: towards an understanding of dyslexia in posterior cortical atrophy.

Visual crowding is a form of masking in which target identification is hindered by excessive feature integration from other stimuli in the vicinity. It has previously been suggested that excessive visual crowding constitutes one specific form of early-visual-processing deficit, which may be observed in individuals with posterior cortical atrophy (PCA). This study investigated whether excessive visual crowding plays a significant role in the acquired dyslexia of two PCA patients, whose reading was characterized by visual paralexias. The patients were administered a series of letter, flanked letter, and word recognition tasks, and the effects of letter spacing and letter confusability upon response accuracy and latency were measured. In both patients, the results showed (a) evidence of excessive visual crowding, (b) a significant interaction between letter spacing and confusability on flanked letter identification tasks, and (c) effects of letter confusability affecting flanked but not unflanked letter identification. However, only mild improvements in reading accuracy were achieved in the experimental manipulations of interletter spacing within words because these manipulations had a dual effect: Increasing spacing improved individual letter identification but damaged whole-word form and/or parallel letter processing. We consider the implications of these results for the characterization of dyslexia in PCA, the design of reading rehabilitation strategies, and the relationship between visual crowding and letter confusability. In particular, we argue that the reading deficits observed in our patients cannot be accounted for solely in terms of a very low signal-to-noise ratio for letter identification, and that an additional crowding deficit is implicated in which excessive integration of fundamental letter features leads to the formation of incorrect letter percepts.

Deficits in Japanese word spelling as an initial language symptom of malignant glioma in the left hemisphere.

BACKGROUND: A good performance status at diagnosis is a prognostic factor in patients with malignant glioma whose median survival is 24 months. As early diagnosis may improve their poor prognosis, we looked for currently unknown initial symptoms among patients in good performance status. METHODS: We chose 17 consecutive patients with malignant glioma in the left frontal and/or temporal lobe whose Karnofsky Performance Status was more than 80. At preoperative evaluation, we administered the Japanese version of the Western Aphasia Battery. RESULTS: The chief complaint was difficulty in speech (n = 6), headache/nausea (n = 4), seizures (n = 5), and uncinate fits (n = 1); one patient was symptom-free. Of the 17 patients, 14 exhibited no motor deficits. In 15 patients, the aphasia quotient exceeded 80, indicating that the overall language deficits were mild. However, in the reading section, their scores on the "spelled kanji (Japanese ideogram) recognition" test (full score = 10) were selectively low (5.3 +/- 1.6 for right-handed individuals with frontal lesions, 6.1 +/- 1.0 for right-handed patients with temporal lesions, 7.2 +/- 2.0 for left-handed/bimanual individuals with frontal/temporal lesions). Their scores on the "spelling kanji" test were 3.0 +/- 1.6, 4.8 +/- 1.2, and 9.4 +/- 0.6, respectively. CONCLUSIONS: Our findings point to the importance of recognizing spelling deficits as an initial symptom of left hemisphere glioma in efforts to identify patients in good performance status whose prognosis may be improved. It would be important to determine if the spelling of alphabetic words is also impaired early in the clinical course of left hemisphere glioma.

Role of inflectional regularity and semantic transparency in reading morphologically complex words: evidence from acquired dyslexia.

We report two patients with acquired phonological dyslexia who have great difficulty reading affixed words. Experiment 1 demonstrates that both patients' reading performance is influenced by the apparent morphological status of words by comparing the patients' reading of suffixed and pseudo-suffixed words. Experiment 2 was designed to examine reading performance of both regularly and irregularly inflected words. Experiment 3 examines the patients' reading of derivational forms with particular emphasis of the role of 'semantic transparency'. Experiment 4 tested both patients' reading of prefixed words. Finally, Experiment 5 examined performance on a lexical decision task using affixed words. These data support models in which regularly formed inflections and semantically transparent derived forms are subjected to decomposition during processing, whereas irregularly inflected forms and semantically opaque forms may be represented independently. Data are discussed with regard to current 'dual mechanism' models of morphological processing as well as connectionist perspectives, with particular emphasis of the types of data that will ultimately be necessary to arbitrate between the rival theories.

Dissociative disturbance in Hangul-Hanja reading after a left posterior occipital lesion.

Since the Korean language has two distinct writing systems, phonogram (Hangul) and ideogram (Hanja: Chinese characters), alexia can present with dissociative disturbances in reading between the two systems. A 74-year-old right-handed man presented with a prominent reading impairment in Hangul with agraphia of both Hangul and Hanja after a left posterior occipital- parietal lesion. He could not recognize single syllable words and nonwords in Hangul, and visual errors were predominant in both Hanja reading and the Korean Boston Naming Test. In addition, he had difficulties in visuoperceptual tests including Judgment of Line Orientation, Hierarchical Navon figures, and complex picture scanning. These findings are consistent with the hypothesis that Hangul reading impairment results from a general visual perceptual deficit. However, this assumption cannot explain why performance on visually complex Hanja was better than performance on visually simple Hanja in our patient. In addition, the patient did not demonstrate higher accuracy on Hanja characters with fewer strokes than on words with more strokes. Thus, we speculate that the left posterior occipital area may be specialized for Hangul letter identification in this patient. This case demonstrates that Hangul-Hanja reading dissociation impairment can occur after occipital-parietal lesions.