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Frontiers of Neurology and Neuroscience 2019Studies of alexia and agraphia have played historically important roles in efforts to understand the relation between brain and behavior. In the second half of the 19th... (Review)
Review
Studies of alexia and agraphia have played historically important roles in efforts to understand the relation between brain and behavior. In the second half of the 19th century, works by Paul Broca and Carl Wernicke led to the concept of delimited cortical centers in the left cerebral hemisphere concerned with discrete aspects of spoken and written language. These specialized centers were linked by white matter pathways. Charlton Bastian, Jean-Martin Charcot, Sigmund Exner, and Jules Dejerine championed center-pathway models of reading and writing. Dejerine played a dominant role, rejecting the idea of a left frontal lobe center that mediated writing and proposing a unique, specialized role for the left angular gyrus in both reading and writing. In 1891 and 1892, he detailed the symptoms of alexia and agraphia that resulted from injury to the left angular gyrus and from the isolation of the left angular gyrus from visual input required for reading. During the early 20th century, his work and that of other so-called diagram makers was confronted and largely discredited by Pierre Marie, joined later by Henry Head and Kurt Goldstein. In the 1960s, the center-pathway model was resurrected and refined by Norman Geschwind. He drew upon foundational works of Dejerine, Hugo Liepmann, and others to describe syndromes resulting from cortical disconnections and, in doing so, helped to establish a framework for the modern discipline of behavioral neurology.
Topics: Agraphia; Dyslexia; History, 19th Century; History, 20th Century; Humans; Neurology; Research
PubMed: 31220840
DOI: 10.1159/000494951 -
Cortex; a Journal Devoted To the Study... Dec 2022While pure alexia was long considered a disconnection syndrome, it may also be a selective visual word agnosia due to damage to the visual word form area. Disconnection...
While pure alexia was long considered a disconnection syndrome, it may also be a selective visual word agnosia due to damage to the visual word form area. Disconnection is still the likely explanation of hemi-alexias, though, particularly when splenial lesions damage inter-hemispheric projections and cause left hemi-alexia. An intra-hemispheric disconnection causing right hemi-alexia is theoretically possible but seems very rare, with only a single report that has been challenged on the grounds of inadequate perimetry. We describe the case of PH, who had a severe reading deficit in her right hemifield. Detailed perimetry showed only a small relative hemi-scotoma along the horizontal meridian, while word reading was impaired over a much larger expanse of her right hemifield, in which object recognition was spared. Reading, lexical decisions, and perceptual discrimination of words were impaired in the right hemifield, and this extended to letters and numbers, with a trend to an effect on the perception of an unfamiliar script, namely Korean. On magnetic resonance imaging she had a large left lateral occipital meningioma with vasogenic edema of occipital white matter tracts. Functional magnetic resonance imaging showed that the visual word form area was located just anterior to the mass. Her perceptual abnormalities resolved after resection of the tumor. We conclude that right hemi-alexia exists and is most likely due to intra-hemispheric disconnection of occipital input to the visual word form area.
Topics: Humans; Female; Dyslexia; Alexia, Pure; Reading; Visual Perception; Magnetic Resonance Imaging
PubMed: 36370599
DOI: 10.1016/j.cortex.2022.09.015 -
Handbook of Clinical Neurology 2021Alexia refers to a reading disorder caused by some form of acquired brain pathology, most commonly a stroke or tumor, in a previously literate subject. In...
Alexia refers to a reading disorder caused by some form of acquired brain pathology, most commonly a stroke or tumor, in a previously literate subject. In neuropsychology, a distinction is made between central alexia (commonly seen in aphasia) and peripheral alexia (a perceptual or attentional deficit). The prototypical peripheral alexia is alexia without agraphia (pure alexia), where patients can write but are impaired in reading words and letters. Pure alexia is associated with damage to the left ventral occipitotemporal cortex (vOT) or its connections. Hemianopic alexia is associated with less extensive occipital damage and is caused by a visual field defect, which creates problems reading longer words and passages of text. Reading impairment can also arise due to attentional deficits, most commonly following right hemisphere or bilateral lesions. Studying patients with alexia, along with functional imaging studies of normal readers, has improved our understanding of the neurobiological processes involved in reading. A key question is whether an area in the left ventral occipitotemporal cortex is specialized for or selectively involved in word processing, or whether reading relies on tuning of more general purpose perceptual areas. Reading deficits may also be observed in dementia and traumatic brain injury, but often with less consistent deficit patterns than in patients with focal lesions.
Topics: Cerebral Cortex; Dyslexia; Humans; Stroke
PubMed: 33832678
DOI: 10.1016/B978-0-12-821377-3.00010-6 -
Annual Review of Clinical Psychology 2015This review uses a levels-of-analysis framework to summarize the current understanding of developmental dyslexia's etiology, brain bases, neuropsychology, and social... (Review)
Review
This review uses a levels-of-analysis framework to summarize the current understanding of developmental dyslexia's etiology, brain bases, neuropsychology, and social context. Dyslexia is caused by multiple genetic and environmental risk factors as well as their interplay. Several candidate genes have been identified in the past decade. At the brain level, dyslexia is associated with aberrant structure and function, particularly in left hemisphere reading/language networks. The neurocognitive influences on dyslexia are also multifactorial and involve phonological processing deficits as well as weaknesses in other oral language skills and processing speed. We address contextual issues such as how dyslexia manifests across languages and social classes as well as what treatments are best supported. Throughout the review, we highlight exciting new research that cuts across levels of analysis. Such work promises eventually to provide a comprehensive explanation of the disorder as well as its prevention and remediation.
Topics: Brain; Child; Dyslexia; Humans; Molecular Biology; Risk Factors
PubMed: 25594880
DOI: 10.1146/annurev-clinpsy-032814-112842 -
Current Opinion in Pediatrics Dec 2016We review current knowledge about the nature of reading development and disorders, distinguishing between the processes involved in learning to decode print, and the... (Review)
Review
PURPOSE OF REVIEW
We review current knowledge about the nature of reading development and disorders, distinguishing between the processes involved in learning to decode print, and the processes involved in reading comprehension.
RECENT FINDINGS
Children with decoding difficulties/dyslexia experience deficits in phoneme awareness, letter-sound knowledge and rapid automatized naming in the preschool years and beyond. These phonological/language difficulties appear to be proximal causes of the problems in learning to decode print in dyslexia. We review data from a prospective study of children at high risk of dyslexia to show that being at family risk of dyslexia is a primary risk factor for poor reading and children with persistent language difficulties at school entry are more likely to develop reading problems. Early oral language difficulties are strong predictors of later difficulties in reading comprehension.
SUMMARY
There are two distinct forms of reading disorder in children: dyslexia (a difficulty in learning to translate print into speech) and reading comprehension impairment. Both forms of reading problem appear to be predominantly caused by deficits in underlying oral language skills. Implications for screening and for the delivery of robust interventions for language and reading are discussed.
Topics: Child; Child Language; Child, Preschool; Comprehension; Dyslexia; Humans; Reading; Risk Factors
PubMed: 27496059
DOI: 10.1097/MOP.0000000000000411 -
International Journal of Language &... Nov 2020Every language has certain specific idiosyncrasies in its writing system. Cross-linguistic analyses of alexias and agraphias are fundamental to understand commonalities...
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.
Topics: Agraphia; Brain; Chile; Databases, Factual; Dyslexia, Acquired; Female; Humans; Language; Language Tests; Linguistics; Male; Middle Aged; Reading; Tomography, X-Ray Computed
PubMed: 32735061
DOI: 10.1111/1460-6984.12566 -
Language, Speech, and Hearing Services... Oct 2018This review summarizes what is known about the structural and functional brain bases of dyslexia. (Review)
Review
PURPOSE
This review summarizes what is known about the structural and functional brain bases of dyslexia.
METHOD
We review the current literature on structural and functional brain differences in dyslexia. This includes evidence about differences in gray matter anatomy, white matter connectivity, and functional activations in response to print and language. We also summarize findings concerning brain plasticity in response to interventions.
RESULTS
We highlight evidence relating brain function and structure to instructional issues such as diagnosis and prognosis. We also highlight evidence about brain differences in early childhood, before formal reading instruction in school, which supports the importance of early identification and intervention.
CONCLUSION
Neuroimaging studies of dyslexia reveal how the disorder is related to differences in structure and function in multiple neural circuits.
Topics: Brain; Child; Child, Preschool; Cognition; Dyslexia; Humans; Neuroimaging; Neuronal Plasticity; Reading
PubMed: 30458541
DOI: 10.1044/2018_LSHSS-DYSLC-18-0020 -
Neurologic Clinics May 2003Peripheral dyslexias are the result of impairment to processes that convert letters on the page into an abstract orthographic representation. Many aspects of these... (Review)
Review
Peripheral dyslexias are the result of impairment to processes that convert letters on the page into an abstract orthographic representation. Many aspects of these disorders are difficult to understand in depth. Invariably, there is evidence that some type of word-level perception occurs rapidly in many patients with LBL reading or neglect dyslexia, yet apparently contradictory evidence indicates that part of the word has been misperceived or that the letters must be analyzed laboriously for conscious identification to occur. Current theories attempt to synthesize these different aspects of the patients' performance, but their development is at an early stage. Questions remain also about the domain specificity of the perceptual impairment in LBL reading and about the nature of spatial attention and spatial frames in neglect dyslexia and other forms of attentional disorder. Current understanding of central dyslexias has perhaps advanced further. Well-developed computational models exist of these dyslexias, as do plausible experimental techniques for revealing the activity of semantic and non-semantic routes in normal readers. Nevertheless, the difficult issue of domain specificity arises again with respect to some of the mechanisms invoked, and in this regard, central and peripheral dyslexias continue to pose the same challenge.
Topics: Attention; Brain Diseases; Dyslexia, Acquired; Humans; Reading; Semantics
PubMed: 12916491
DOI: 10.1016/s0733-8619(02)00099-3 -
Topics in Stroke Rehabilitation 2004Alexia is an acquired disturbance in reading. Alexias that occur after left hemisphere damage typically result from linguistic deficits and may occur as isolated... (Review)
Review
Alexia is an acquired disturbance in reading. Alexias that occur after left hemisphere damage typically result from linguistic deficits and may occur as isolated symptoms or as part of an aphasia syndrome. This article presents an overview of the classification of the alexias, including both the traditional neuroanatomical perspective and the more recent psycholinguistic approach. Then, assessment procedures are reviewed, followed by a summary of treatment approaches for alexia. Finally, two case studies illustrate how oral reading of connected language (sentences and paragraphs rather than single words) has been used as a technique for treating alexia in patients with aphasia.
Topics: Aphasia; Dyslexia, Acquired; Humans; Models, Psychological; Reading; Rehabilitation; Stroke
PubMed: 14872397
DOI: 10.1310/VUPX-WDX7-J1EU-00TB -
Frontiers of Neurology and Neuroscience 2019The kanji and kana (or kanji vs. kana) problem in the Japanese language denotes the dissociation between kanji (morphograms) and kana (phonograms) in... (Review)
Review
The kanji and kana (or kanji vs. kana) problem in the Japanese language denotes the dissociation between kanji (morphograms) and kana (phonograms) in reading/comprehension and writing. Since paragraphia of kana in a patient with amyotrophic lateral sclerosis was first reported in 1893, kanji-kana dissociation has been the central topic in Japanese aphasiology. Recent advancements in lesion-to-symptom analyses and functional imaging studies have identified some areas whose damage causes dissociative disturbances of reading or writing between kanji and kana. That is, (1) angular alexia with agraphia causes kanji agraphia; alexia of kana with an angular gyrus lesion is the result of a damage to the middle occipital gyrus; (2) alexia with agraphia for kanji is caused by a posterior inferior temporal cortex (mid-fusiform/inferior temporal gyri; visual word form area) lesion, whereas pure agraphia for kanji is caused by a posterior middle temporal gyrus lesion; and (3) pure alexia, particularly for kanji, results from a mid-fusiform gyrus lesion (Brodmann's Area [BA] 37), whereas pure alexia for kana results from a posterior fusiform/inferior occipital gyri lesion (BA 18/19).
Topics: Agraphia; Brain Mapping; Diagnosis, Differential; Dyslexia; History, 20th Century; Humans; Japan; Occipital Lobe; Reading; Writing
PubMed: 31220841
DOI: 10.1159/000494952