Regional cerebral blood flow in severe developmental dyslexia

Learning Difficulties: Neuropsychological Interpretations and Interventions

Learning difficulties affect up to 20 percent of school-aged children. While many children “grow out” of their disability, a significant proportion experience ongoing problems which can hinder academic, social, and emotional development.

Neuropsychological models suggest that these children may suffer from subtle deficits in memory and organizational abilities, which make them vulnerable within a classroom environment. Understanding the specific neuropsychological strengths and weaknesses of children with learning difficulties may provide information regarding the most appropriate form of intervention and the likelihood of its success.

In recent study at the Royal Children's Hospital, Melbourne, 160 learning disabled children were evaluated. Findings from the group suggested a high frequency of general health problems as well as mild episodes of central nervous system dysfunction. Neuropsychological data showed that the sample, as a whole, performed within the average range on standardized intellectual measures, but achieved poor results on measures of new learning and executive function. Furthermore, data supported the presence of a number of patterns of learning disability, including linguistic deficit, non-verbal deficit, and information processing deficit. These subtypes are discussed with reference to educational characteristics, and models of intervention are suggested.

Comparative study of the neuropsychological and neuroimaging evaluations in children with dyslexia

We analyzed retrospectively the neuroimaging exams of children with a confirmed diagnosis of dyslexia and correlated our findings with the evaluation of higher cortical functions. We studied 34 medical files of patients of the Ambulatory of Neuro-difficulties in Learning, FCM/UNICAMP. All of them had been sent to the ambulatory with primary or secondary complaints of difficulties at school and were submitted to neuropsychological evaluation and imaging exam (SPECT). From the children evaluated 58.8% had exams presenting dysfunction with 47% presenting hypoperfusion in the temporal lobe. As for the higher cortical functions, the most affected abilities were reading, writing and memory. There was significance between the hypoperfused areas and the variables schooling, reading, writing, memory and mathematic reasoning. The SPECTs showed hypoperfusion in areas involved in the reading and writing processes. Both are equivalent in terms of involved functional areas and are similar in children with or without specific dysfunctions in neuroimaging.

Interhemispheric asymmetry of regional cerebral blood flow in prepubescent boys with attention deficit hyperactivity disorder

The prefrontal cortex is asymmetric in both structure and function. In normal subjects, the right prefrontal cortex is activated more than the left during response inhibition. Patients with attention deficit hyperactivity disorder (ADHD) have impaired response inhibition and altered structural interhemispheric asymmetry. This study was conducted to examine the functional interhemispheric asymmetry during response inhibition in children with ADHD. Subjects were divided into three groups according to the level of motor hyperactivity. Blood flow tracer (99m)Tc-ethyl cysteinate dimer was injected while subjects were performing a response inhibition task (RIT), followed by single photon emission computerized tomography (SPECT). After three-dimensional reconstruction, filtering and smoothing, individual scans were morphed to a template. Three average group images were created from individual scans. Each average group image was subtracted voxel-by-voxel from its mirror image to compare the regional cerebral blood flow (rCBF) in the right and left cerebral hemispheres, yielding images of significant interhemispheric rCBF asymmetry. The severe hyperactivity group exhibited most prefrontal left>right rCBF asymmetry and left>right occipitoparietal asymmetry. Reversal of functional prefrontal asymmetry in boys with severe motor hyperactivity supports the hypothesis of right prefrontal cortex dysfunction in ADHD.

Magnetic resonance technology in human brain science: blueprint for a program based upon morphometry

Magnetic resonance images provide a comprehensiveness of analysis of the human brain and levels of resolution never achieved by other modes of pathoanatomic analysis. We review a strategy and technology of MRI-based image analysis which extracts independent measures of brain volumes, shape and position. These parameters are readily correlated with behavioral as well as physiological measures derived from PET and the emerging technology of MRI-based in vivo spectroscopy. A coordinate program which draws upon these methods will have wide applications in human brain science and the study of dynamic properties of human brain disease.

Visual half-field contrast sensitivity in children with dyslexia

We address the question whether left-hemispheric and/or right-hemispheric contrast thresholds differ between children with dyslexia and controls, and whether there are interhemispheric differences. In order to answer these questions we examined [1] thresholds for the detection of Contrast-Defined (CD) forms to left and right half-field stimulation, and [2] half-field pattern onset Evoked Potentials (EPs) as a function of stimulus contrast in 21 children with dyslexia of 8-15 years of age and in 17 age-matched healthy controls. It was found that (A) children with dyslexia were less sensitive to CD forms than controls irrespective of half field of stimulation. In children with dyslexia as well as controls the forms were more easily detected in the right visual half-field than in the left one: (B) Peak latencies of the pattern onset EPs to contrast levels above 20% were up to 10 ms longer in children with dyslexia than in controls irrespective of half field of stimulation, and (C) children with dyslexia had smaller mean amplitudes for all contrast levels used. (D) Neither children with dyslexia nor controls showed hemispheric differences in the pattern onset EPs.

Semantic cortical activation in dyslexic readers

The combined temporal and spatial resolution of MEG (magnetoencephalography) was used to study whether the same brain areas are similarly engaged in reading comprehension in normal and developmentally dyslexic adults. To extract a semantically sensitive stage of brain activation we manipulated the appropriateness of sentence-ending words to the preceding sentence context. Sentences, presented visually one word at a time, either ended with a word that was (1) expected, (2) semantically appropriate but unexpected, (3) semantically anomalous but sharing the initial letters with the expected word, or (4) both semantically and orthographically inappropriate to the sentence context. In both subject groups all but the highly expected sentence endings evoked strong cortical responses, localized most consistently in the left superior temporal cortex, although additional sources were occasionally found in more posterior parietal and temporal areas and in the right hemisphere. Thus, no significant differences were found in the spatial distribution of brain areas involved in semantic processing between fluent and dyslexic readers. However, both timing and strength of activation clearly differed between the two groups. First, activation sensitivity to word meaning within a sentence context began about 100 msec later in dyslexic than in control subjects. This is likely to result from affected presemantic processing stages in dyslexic readers. Second, the neural responses were significantly weaker in dyslexic than in control subjects, indicating involvement of a smaller or less-synchronous neural population in reading comprehension. Third, in contrast to control subjects, the dyslexic readers showed significantly weaker activation to semantically inappropriate words that began with the same letters as the most expected word than to both orthographically and semantically inappropriate sentence-ending words. Thus, word recognition by the dyslexic group seemed to be qualitatively different: Whereas control subjects perceived words as wholes, dyslexic subjects may have relied on sublexical word recognition and occasionally mistook a correctly beginning word for the one they had expected.

Evidence from imaging on the relationship between brain structure and developmental language disorders

This article discusses findings using various imaging techniques regarding the neurological underpinnings of developmental language and learning disorders. Evidence from magnetic resonance imaging, functional magnetic resonance imaging, single photon emission spectroscopy, and positron emission tomography implicates the left perisylvian regions in the processing of phonemes and auditory information, as had been predicted from lesion data and from neurobiological theory. The areas of the planum temporale and angular gyrus have been found to be compromised in children and adults with dyslexia or language impairment. Emerging evidence suggests that these differences are also present in members of families with a history of developmental language disorders, which provides support for a transmittable, biological factor involved in such disorders. Dynamic imaging procedures are beginning to provide an understanding of the relationship between structure and function in normal and abnormal language acquisition.

Types of dyslexia and the shift to dextrality

The prediction of the right shift theory that there are two types of dyslexia with different distributions of handedness was examined in a large cohort of school children. Dyslexics with poor phonology were less biased to dextrality than controls, while dyslexics without poor phonology tended to be more dextral than controls on measures of hand preference and hand skill. Relatives also differed for handedness, as expected if phonological dyslexics were less likely than nonphonological dyslexics and controls to carry the hypothesized rs + gene.

Brain basis for dyslexia: a summary of work in progress

Studies of brain/behavior relations in the last decade have converged to suggest a left-hemisphere functional deficit for dyslexia. The relationship is most convincing at the microscopic level, where anomalous neural organization has been associated with reading, and at the macroscopic level, where several studies find atypical hemispheric symmetry in the language-related temporal region in individuals with dyslexia. Physiological studies measuring brain function during cognitive challenge have now begun to accumulate in support of a left-hemisphere deficit in dyslexia. This article summarizes work in progress on the structure and physiological profiles of reading disability and relates the findings to core left-hemisphere language functions.

Season of birth and neurodevelopmental disorders: summer birth is associated with dyslexia

OBJECTIVE

Increased risk for certain psychiatric disorders has been associated with season of birth. This study was undertaken to look for hypothesized season-of-birth effects for dyslexia, schizophrenia spectrum disorders, and neurological soft signs in children and adolescents.

METHOD

Month of birth and the diagnostic findings in question were examined based on charts from a clinic population of 585 boys. Odds ratios and etiological fractions were calculated.

RESULTS

Neurological soft signs showed a sporadic peak for June births and schizophrenia spectrum showed a peak for August and November. A smooth curve suggesting true seasonality was evident in dyslexia for births in May, June, and July. For different 5-year birth cohorts, early summer birth accounts for 24 to 71% of cases of dyslexia.

CONCLUSIONS

The authors suggest that viral infection, especially influenza, during the second trimester of pregnancy is the most attractive hypothesis to explain these findings. If this hypothesis is supported, immunization in women of child-bearing age could reduce the incidence of dyslexia. Secondary prevention could also be enhanced by early identification and treatment of children who were exposed in utero.

Positron emission tomographic studies during serial word-reading by normal and dyslexic adults

Positron-emission tomography (PET) was used to study regional cerebral metabolic activity during oral reading in right-handed adult males with, and without a childhood and family history of developmental dyslexia. Significant group differences in normalized regional metabolic values were revealed in prefrontal cortex and in the lingual (inferior) region of the occipital lobe. Lingual values were bilaterally higher for dyslexic than normal readers. In contrast to the asymmetry observed in prefrontal and lingual regions in nondyslexic subjects during reading, the dyslexic pattern was more symmetric. These results demonstrate that individuals who suffered from familial developmental dyslexia as children, activate different brain regions during reading as adults, as compared to individuals without such childhood history.

Neuropsychological divergence of high-level autism and severe dyslexia

The relationship between cognitive deficits in high-level autism and those in learning disabilities has received little attention. To determine whether high-functioning autistic patients and individuals with severe dyslexia display different cognitive characteristics, 10 nonretarded men (mean age 26 years) with infantile autism, residual state, were compared with 15 severely dyslexic men (mean age 22 years) and 25 matched controls on a neuropsychological test battery. The two clinical groups were dissociated by a reduced digit span seen in the dyslexics and by impaired problem-solving skills (Wisconsin Card Sort and selected subtests from the Binet) seen in the autistic group. These results suggest different localization of brain dysfunction and different educational/habilitative needs.

Neurophysiological heterogeneity and the definition of dyslexia: preliminary evidence for plasticity

Developments in the field of quantified electroencephalography have enhanced visualization of brain function in the learning disabilities. Optimal utilization of these techniques requires that populations under study be unambiguously defined. Evidence from the literature demonstrates that brain electrical activity of children with reading disability is more extensive and differs from that seen in children with "dyslexia-pure". Preliminary data are presented demonstrating that electrophysiological change seen in children with dyslexia-plus (dyslexia and attentional deficit disorder) could not be predicted by knowledge of electrophysiologic change in children with dyslexia-pure alone and attentional deficit disorder alone. Data from our laboratory are summarized to show that within dyslexia-pure the anomic, dysphonemic and global Denckla subtypes differ electrophysiologically from one another. Of particular interest is the demonstration that regions of electrophysiological difference among these subtypes may reflect compensatory mechanisms rather than pathological change. Finally, a case study is presented demonstrating advantageous effects of remediation upon brain electrical function. As both spontaneous and environmentally induced change in brain function can be documented, developmental dyslexia in its broadest terms appears to represent a more dynamic or plastic process than previously appreciated.

EEG spectra in severely dyslexic men: rest and word and design recognition

To identify and localize differences in brain functioning, electrical activity was recorded with a full complement of scalp electrodes in 14 healthy, severely dyslexic men (mean age = 22 years, S.D. = 3) and 15 matched controls during rest and during word and design recognition. The electroencephalograms were spectrum analyzed, and the mean amplitude in each of 5 bands--delta, theta, alpha, slow beta and fast beta--compared topographically between conditions and groups. The two tasks did not elicit differentially lateralized patterns of electrical activity, but produced anteroposterior differences in alpha and theta. The Designs task, more difficult for both groups, was associated with less posterior alpha than was the Words task. The strongest group difference was likewise seen along an anteroposterior axis on the Designs task. With performance equal to that of controls, the dyslexics showed relatively greater fronto-central theta and less posterior theta (a more activated state), suggesting that dyslexics were compensating for less efficient information processing. There were no group differences in overall amplitude in any band for any condition. The differences in the topographic distribution of theta may reflect subtle differences in brain organization or compensatory recruitment of widely distributed neuronal networks.

Childhood dysgraphia. Part 1. An illustrated clinical classification

In this paper we propose a clinical neurological classification of childhood dysgraphia (medical model). The subject is introduced by briefly considering the childhood learning disorders as a whole, and subsequently dysgraphia will be considered in particular with description and illustration of the different types. In our second paper we report a detailed neuropsychological study which we made of 66 children with dysgraphia. In view of the differing definitions used between professionals, this first paper is an attempt to define the terms used in our classification so that subsequent statistical analysis of individual factors in aetiology and neurology can be interpreted.