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At least 19 recordsLinked to original sources
PubMed1992

Neurology of developmental dyslexia.

Developmental dyslexia has until recently been considered to belong solely in the domain of educational psychology. With the advent of better theories on language and reading, and better methods for assessing the structure and function of living human brains and for determining genetic transmission, dyslexia is now poised to become a focal concern of cognitive neuroscience and genetic research. Recent findings from neuroanatomy, neurophysiology, neuropsychology, and genetics research are reviewed.

Brain↗
PubMed2026

Predicting training outcomes for developmental dyslexia from EEG data.

Developmental dyslexia (DD) is characterised by lower-than-average reading abilities and is diagnosed in approximately 10% of individuals. The societal barriers may limit professional fulfilment and psychological wellbeing of individuals with DD, calling for the development of effective interventions to counteract them. As DD is associated with challenges in both phonological and visuo-attentional domains, different longitudinal training approaches were developed to strengthen them. However, they require a considerable amount of personal, social and economic resources and the outcomes may vary depending on individual differences in behavioural and neurophysiological functionality. Hence, predicting training outcomes might help in developing personalised treatment protocols and optimising the use of resources. In the present work we applied machine learning to resting-state EEG to predict longitudinal training outcomes in adults with DD enrolled in a randomized clinical trial. In particular, one group received a visuo-attentional training combined with transcranial alternating current stimulation (tACS), another group received visuo-attentional training with sham/placebo stimulation, and the third group received a phonological training with sham/placebo stimulation. The improvement in text reading speed was associated with spectral power in low-beta and individual frequencies in the alpha (IAF) and beta (IBF) bands, while the improvement in pseudoword reading was associated with IBF. The findings highlight the potential of capturing neural markers of treatment responsiveness in DD. Future studies should focus on the generalisability of predictive models to real-world settings, while investigating whether specific EEG markers predict responsiveness to distinct remediation protocols, thus supporting the development of personalised interventions.

Humans↗
PubMed1991

Evidence for major gene transmission of developmental dyslexia.

OBJECTIVE: --There is strong evidence that developmental dyslexia is both familial and heritable, but the mode of genetic transmission has remained unclear. In this article, we examine specific genetic hypotheses about the mode of transmission of developmental dyslexia by performing complex segregation analyses. DESIGN: --A family study method was applied, whereby the relatives of dyslexic probands were examined for dyslexia. The families studied represent four independently ascertained samples. SETTING: --The four samples of families were primarily from rural and suburban communities of Colorado, Washington State, and Iowa. PARTICIPANTS: --A total of 204 families and 1698 individuals in the four samples combined. MAIN OUTCOME MEASURES: --The complex segregation program, POINTER, was used to test competing genetic hypotheses of how a categorical trait (dyslexia) is transmitted in families. RESULTS: --The results were consistent with major locus transmission in three of four samples and with polygenic transmission in the fourth. In these three samples, the estimates of penetrance for the AA, Aa, and aa genotypes (where A is the abnormal allele) were, respectively, 1.000, 1.000, and 0.001 to 0.039 in males, and 0.560 to 1.000, 0.550 to 0.897, and 0.000 in females. The estimated gene frequency of the major locus was between 3% and 5%. CONCLUSIONS: --Sex-influenced, additive, or dominant transmission occurs in a significant proportion of dyslexic families. Other evidence indicates, however, that dyslexia is etiologically heterogeneous and that there is genetic heterogeneity even among families selected for apparent dominant transmission. Thus, while no single major locus may account for all of dyslexia, it is important to pursue potential major loci for dyslexia using linkage techniques.

Adult↗
PubMed1977

Developmental dyslexia: two right hemispheres and none left.

Developmental dyslexia may be associated with (i) bi-hemisphere representation of spatial functions, in contrast to the right-hemisphere specialization observed in normal children, and (ii) typical left-hemisphere representation of linguistic functions, as is observed in normal children. The bilateral neural involvement in spatial processing may interfere with the left hemisphere's processing of its own specialized functions and result in deficient linguistic, sequential cognitive processing and in overuse of the spatial, holistic cognitive mode. This pattern of cognitive deficits and biases may lead dyslexics to read predominantly with a spatial-holistic cognitive strategy and neglect the phonetic-sequential strategy. Such an approach in learning to read phonetically coded languages, such as English, many be inefficient and limited.

Adolescent↗
PubMed1990

Rate variables and automatized naming in developmental dyslexia.

The rate variable in rapid automatized naming (RAN) was investigated in 50 adolescent and 40 adult students with developmental dyslexia, in matched normal controls, and in learning-disabled students without reading difficulties. Visual stimuli depicting familiar colors and common objects were presented in isolation at three film speeds and three exposure times. Film speed and exposure time contributed as independent variables to error rate; and dyslexic subjects of both age groups made significantly more naming errors than controls. Dyslexic subjects also responded with longer naming latencies than controls when the same RAN stimuli were presented in a continuous sequential mode as a matrix of rows and columns. Naming latencies in the sequential presentation were highly correlated with naming errors in the film version. The implications of reduced naming rates for nongraphological stimuli in developmental dyslexia are discussed.

Adolescent↗
PubMed1988

The failure of antimotion sickness medication to improve reading in developmental dyslexia: results of a randomized trial.

Although there have been no randomized clinical trials of the efficacy of antimotion sickness medication treatment of developmental dyslexia, some children are treated in this way. We have performed two evaluations of such treatments. In Experiment 1, 12 children participated in a double-blind within-subject crossover design to test the acute (2-day) administration of four preparations: 10 mg methylphenidate, 12.5 mg meclizine, both methylphenidate and meclizine, or placebo. Improvements obtained with each drug were scattered across measures of reading fluency, balance and coordination, and eye movements, suggesting that a chronic trial would be justified. In Experiment 2, six children from Experiment 1 received 12.5 mg meclizine b.i.d. for 3 months and placebo for 3 months in a double-blind within-subject crossover design. Meclizine had no effect on reading, but it significantly improved ocular motor stability during steady fixation. This study thus failed to support the hypothesis that meclizine is of benefit in developmental dyslexia.

Child↗
PubMed1991

Word-finding ability and design fluency in developmental dyslexia.

Certain oral as well as visual language disorders now appear characteristic of the developmental dyslexia syndrome. Recent research has revealed word-finding difficulties in dyslexic children but has left unanswered questions about specificity and causality. Verbal and non-verbal fluency in dyslexics and non-dyslexic CA- and RA-matched controls were measured by means of cued lexical retrieval and stick design tasks. Evidence for dyslexia-related difficulties was found only at the word form level of access. At the semantic level, dyslexics' word finding was superior. Non-verbal (design) fluency was normal. Such findings implicate long-term linguistic memory processes in dyslexia and are consistent with neurocognitive models that emphasize diffuse left hemisphere dysfunction.

Attention↗
PubMed1978

Developmental dyslexia. Evidence for a subgroup with a reversal of cerebral asymmetry.

The computerized brain tomograms of 24 patients with developmental dyslexia were analyzed for cerebral asymmetry. Ten patients showed a reversal of the pattern of asymmetry regularly observed in normal right-handed individuals so that the right parietooccipital region was wider than the left. The ten dyslexic patients with this reversal of cerebral asymmetry had a lower mean verbal IQ than the other 14 dyslexic patients in this study. The reversal of cerebral asymmetry that occurred in ten of the dyslexic patients may result in language lateralization to a cerebral hemisphere that is structurally less suited to support language function and thus act as a risk factor for the development of reading disability.

Adolescent↗
PubMed1992

Dichotic listening performance in subtypes of developmental dyslexia and a left temporal lobe brain tumor contrast group.

This study examined dichotic listening performance in three subtypes of developmental dyslexia and in children with left temporal lobe brain tumors (clinical contrast group). Each child was administered a free-recall CV syllable dichotic paradigm (30 pairs). Analysis of variance and Tukey-HSD pairwise follow-up comparison indicated that the dichotic listening performance of the left temporal lobe brain tumor contrast group (strong LEA/right ear suppression) was significantly different from those of the visual-spatial/dyseidetic (strong REA/left ear depression) and mixed (moderate REA/bilateral ear suppression) dyslexic subtypes. The language disorder/dysphonetic dyslexic subtype demonstrated a REA with right ear depression. Closer inspection of the individual performances of the language disorder/dysphonetic dyslexic subtype revealed a bimodal distribution with 12 subjects demonstrating a strong LEA/right ear suppression and 8 subjects exhibiting a strong REA/left ear depression. These results lend support for the contention that the dyslexic population is heterogeneous in nature with each subgroup exhibiting (1) a distinct neuropsychological test profile and reading pattern and (2) a pattern of performance on the dichotic listening task which is consistent with what would be expected based upon the pattern of dysfunction exhibited on neuropsychological evaluation.

Adolescent↗
PubMed1977

A neurophysiological basis of developmental dyslexia.

Recent advances in the understanding of the asymmetrical functions of the cerebral hemispheres provide new insight to the mechanisms underlying the developmental language disorders. It is probable that learning to read depends in part upon the ability to establish an association between a seen object (customarily perceived within the right hemisphere) and a verbal symbol (mediated by the left). It is possible that as the reading skill develops, verbal symbol recognition may also become a left hemisphere function. A complex interaction between the two developing hemispheres is involved. A clue to the nature of this problem is that developmental dyslexia is six times more common in boys than in girls. Studies defining differences in cerebral dominance in boys and girls will be reviewed in this context.

Auditory Perception↗
PubMed1988

Developmental dyslexia and word retrieval deficits.

Developmental dyslexics, selected on the basis of very slow naming rates on the Rapid Automatic Naming Tasks (RAN), were compared to normal readers on oral language, picture categorization, and reading tasks. Findings indicated that the dyslexics' word retrieval deficits were one symptom of a more generalized, however subtle, oral language deficit which involved both receptive and expressive oral language functioning. The dyslexics' word retrieval problem also seemed chiefly related to language processing and not to deficits in semantic memory as there were no significant differences between dyslexics and controls on a nonverbal semantic memory task (picture categorization). In naming and identifying printed words, the dyslexics appeared to rely considerably upon the "indirect" or "assembly-of-phonology" route; they were slower in naming irregularly spelled words compared to regularly spelled words and on a lexical decision task, the dyslexics were slower in making negative decisions for "pseudohomophones" (e.g., "braik") than for other matched nonwords. Results are discussed in terms of the logogen model with some consideration of a developmental model as well.

Anomia↗
PubMed1990

MRI evaluation of the size and symmetry of the planum temporale in adolescents with developmental dyslexia.

MRI technique was used to examine the size and symmetry of the plana temporale in 19 dyslexic students in grade 8 and in carefully matched control subjects. The results demonstrated a high frequency of planum symmetry among the dyslexics (70%) whereas symmetry was observed in only 30% of the control subjects. It was not possible to demonstrate any clear association between symmetry/asymmetry of planum temporale and handedness. Word-reading strategies among the dyslexics and control subjects were investigated with computerized tasks where accuracy and naming latency were recorded. All subjects with pure phonological deficits in reading had symmetrical plana temporale indicating a possible neuroanatomical basis for a characteristic symptom of linguistic processing deficiency in developmental dyslexia.

Adolescent↗
PubMed1992

Language abilities, reading acquisition, and developmental dyslexia: a discussion of hypothetical and observed relationships.

Tests of a model of the expected relationships between language abilities and reading achievement measures from the beginning of kindergarten through third grade are discussed. At kindergarten, more global language abilities influenced early, wholistic measures of reading achievement, including letter and number naming. At Grade 1, these earlier accomplishments had a direct effect on word recognition, but a second direct effect was also apparent for word and pheneme segmentation measured in kindergarten. Comprehension at Grade 1 was influenced primarily by word recognition abilities at the same time. At Grade 2, comprehension influenced word recognition; at Grade 3, word recognition and comprehension were essentially independent. These findings are considered in the context of Frith's three-phase hypothesis of reading acquisition. A rationale for testing the potential of training in auditory segmentation to modulate the effects of developmental dyslexia is presented.

Aptitude↗
PubMed1991

Physiological and anatomical evidence for a magnocellular defect in developmental dyslexia.

Several behavioral studies have shown that developmental dyslexics do poorly in tests requiring rapid visual processing. In primates fast, low-contrast visual information is carried by the magnocellular subdivision of the visual pathway, and slow, high-contrast information is carried by the parvocellular division. In this study, we found that dyslexic subjects showed diminished visually evoked potentials to rapid, low-contrast stimuli but normal responses to slow or high-contrast stimuli. The abnormalities in the dyslexic subjects' evoked potentials were consistent with a defect in the magnocellular pathway at the level of visual area 1 or earlier. We then compared the lateral geniculate nuclei from five dyslexic brains to five control brains and found abnormalities in the magnocellular, but not the parvocellular, layers. Studies using auditory and somatosensory tests have shown that dyslexics do poorly in these modalities only when the tests require rapid discriminations. We therefore hypothesize that many cortical systems are similarly divided into a fast and a slow subdivision and that dyslexia specifically affects the fast subdivisions.

Adult↗
PubMed1990

Abstract letter identities and developmental dyslexia.

Four experiments, first used by Bigsby (1988a), were presented to three groups of competent readers of varying reading ages and to nine developmentally dyslexic children. As in the initial study, competent reader data were analysed using group statistical analysis techniques together with some discussion of individual experimental effects and error levels. Competent reader data were also analysed, as were data from the dyslexic subjects, at a cognitive functional level and individual processing descriptions were obtained. Results from the group analysis confirmed earlier findings that nominal matches engage an abstract letter identity (ALI) code which has a similar capacity to the visual code and that, when the ALI code of a reversible letter (b, d, p, q) is accessed, an extra processing step is probably involved. Individual processing descriptions revealed that several of the dyslexic subjects displayed major impairments in ALI coding while some of the competent readers showed mild inefficiencies. A developmental trend towards greater processing efficiency was noted, using both methods of analysis, for the competent reader sample. It is concluded that results are consistent with those models of word recognition which depict ALI coding as a necessary prerequisite to word recognition.

Attention↗
PubMed1990

Brain morphology in developmental dyslexia and attention deficit disorder/hyperactivity.

This study examined the specificity of deviations in patterns of normal brain asymmetry on the magnetic resonance imaging scans of 10 dyslexic, 10 attention deficit disorder/hyperactivity (ADD/H), and 10 normal age- and sex-matched control children. Reliabilities of region of interest measurements for left and right anterior and posterior width and area, length of the bilateral insular region, and length of the bilateral planum temporale were excellent. Both the dyslexic and ADD/H children had significantly smaller right anterior-width measurements than did normal subjects. The dyslexics also had a bilaterally smaller insular region and significantly smaller left planum temporale than did the normal subjects. Seventy percent of the normal and ADD/H children had the expected left greater than right pattern of plana asymmetry, while only 10% of the dyslexic children did. The very significant increase in the incidence of plana symmetry or reversed asymmetry seems unique to dyslexia and may be related to deviations in normal patterns of corticogenesis. Although significantly more dyslexic children were left-handed than were the normal and ADD/H children, no significant relationship emerged between left-handedness, incidence of allergies or familial autoimmune disease, and variability in indexes of brain morphologic findings.

Analysis of Variance↗
PubMed1990

Developmental dyslexia in women: neuropathological findings in three patients.

Brains from male cases with dyslexia show symmetry of the planum temporale and predominantly left-sided cerebrocortical microdysgenesis. We now report on three women with dyslexia. In all brains, the planum temporale was again symmetrical. Also, in two of the brains, multiple foci of cerebrocortical glial scarring were present. In both women, many of the scars were myelinated, suggesting origination during late intrauterine or early postnatal life. In one, scars were mainly left perisylvian and involved portions of the vascular border zone of the temporal cortex. In the other, scars were more numerous and occurred in the border zone of the anterior, middle, and posterior cerebral arteries symmetrically. All three cases showed to a variable extent brain warts, molecular layer ectopias, and focal architectonic dysplasia identical to those seen in the male cases. Two women had primary brain neoplasms, an oligodendroglioma and a low-grade astrocytoma, respectively, and two women showed small angiomas. Reexamination of previously reported male cases disclosed one with myelinated glial scars. Two control brains with asymmetrical plana temporale showed myelinated glial scars as well. The significance of the anatomical findings is discussed, and possible etiological factors are considered with known effects of autoimmune diseases on the nervous system.

Adult↗