Biomedical subjects

G W Hynd

Publications and source records attributed to G W Hynd.

At least 37 records · Page 2Linked to original sources

PubMed1993

Anomalous cerebral structure in dyslexia revealed with magnetic resonance imaging.

OBJECTIVE: To develop quantitative methods for identifying cerebral anomalies on magnetic resonance images of subjects with language disorders and other learning disabilities. DESIGN: Partially blinded comparison of subjects with dyslexia, unaffected relatives, and a control group balanced for age and socioeconomic status. Criterion standard: clinical diagnosis of dyslexia by physician or learning disabilities specialist on the basis of clinical assessment and family history. SETTINGS: Hospital pediatric neurology clinic and private reading clinic. PATIENTS AND OTHER PARTICIPANTS VOLUNTEERS: individuals with dyslexia (seven male and two female, aged 15 to 65 years) from professional families; unaffected first- and second-degree relatives (four male and six female, aged 6 to 63 years) available in the geographical area; and controls (five male and seven female, aged 14 to 52 years). INTERVENTIONS: Gradient echo three-dimensional scan in Seimens 1-Tesla Magnetom; 128 1.25-mm consecutive sagittal images. MAIN OUTCOME MEASURES: (1) Average length of the temporal (T) and parietal (P) banks of the planum temporale; (2) interhemispheric coefficients of asymmetry for T and P banks: Left-Right interhemispheric coefficients of asymmetry = (L-R)/[(L+R)/2]; (3) intrahemispheric coefficients of asymmetry = (T-P)/[(T+P)/2]; and (4) qualitative assessment of gyral variants in the parietotemporal operculum. RESULTS: All groups had left-sided asymmetry for the temporal bank and right-sided asymmetry for the parietal bank. The group with dyslexia had exaggerated asymmetries, owing to a significant shift of right planar tissue from the temporal to parietal bank. They also had a higher incidence of cerebral anomalies bilaterally (subjects with dyslexia, six of nine; relatives, two of 10; and controls, zero of 12). CONCLUSIONS: Quantitative assessment of high-resolution magnetic resonance images can reveal functionally relevant variations and anomalies in cerebral structure. Further refinement of these measurement techniques should improve the diagnosis, classification, and treatment of language disorders and other learning disabilities.

Adolescent↗

PubMed1993

Attention deficit-hyperactivity disorder and asymmetry of the caudate nucleus.

The neurologic basis of attention deficit-hyperactivity disorder (ADHD) is poorly understood. Based on previous studies that have implicated metabolic deficiencies in the caudate-striatal region in ADHD, we employed magnetic resonance imaging to investigate patterns of morphology of the head of the caudate nucleus in normal and ADHD children. In normal children, 72.7% evidenced a left-larger-than-right (L > R) pattern of asymmetry, whereas 63.6% of the ADHD children had the reverse (L < R) pattern of asymmetry of the head of the caudate nucleus. This reversal of normal asymmetry in ADHD children was due to a significantly smaller left caudate nucleus. The reversal in asymmetry of the head of the caudate was most notable in ADHD males. These results suggest that normal (L > R) morphologic asymmetry in the region of the caudate nucleus may be related to asymmetries observed in neurotransmitter systems implicated in ADHD. The behavioral symptoms of ADHD may reflect disinhibition from normal levels of dominant hemispheric control, possibly correlated with deviations in asymmetric caudate-striatal morphology and deficiencies in associated neurotransmitter systems.

Acetyltransferases↗

PubMed1993

Definitional issues and neurobiological foundations of selected severe neurodevelopmental disorders.

This article reviews current definitional issues, selected neuropsychological findings, and presumed neurobiological underpinnings of two of the more commonly identified severe neurodevelopmental disorders: mental retardation and autistic disorder. Although these disorders represent two of the more common severe neurodevelopmental disorders encountered by child neuropsychologists practicing in clinical and research settings, they have not received the amount of attention from the field of neuropsychology as other kinds of neurodevelopmental disorders. Although there are few definitional controversies surrounding these disorders, findings accrued to date reveal solid evidence for neurological processes underlying each of these disorders. In addition, each of these diagnoses likely represents a heterogeneous group of disorders, suggesting that a syndrome analysis approach would prove beneficial for increasing our understanding of each disorder. Conclusions are drawn for the clinician and researcher, particularly with respect to using a neuropsychological perspective and assessment strategies with children with more severe disorders.

Journal Article↗

PubMed1992

Neurological aspects of dyslexia: comment on the balance model.

The Balance Model rests on a long history of research that suggests that different subtypes of dyslexia exist. Based on the notion that there are two subtypes of dyslexia, Bakker has articulated a developmental neuropsychological model whereby a procedure known as hemisphere-specific stimulation may be beneficial in treatment. This article reviews Bakker's model and provides a critical examination as to why validating research has not been conducted. While Bakker's Balance Model may hold promise for scientific inquiry, validation of treatment effects are needed prior to employing these procedures in clinical practice. Further, important conceptual issues remain to be addressed.

Child↗

PubMed1992

Clinical differentiation of the attention deficit disorder subtypes: do sensorimotor deficits characterize children with ADD/WO?

Previous researchers found that children with Attention Deficit Disorder Without Hyperactivity (ADD/WO) tended to perform more poorly than children with Attention Deficit Disorder With Hyperactivity (ADD/H) on measures of motor and sensory functions. In the present study, a prototype sensorimotor soft sign battery was developed which limited cognitive involvement. It was hypothesized that ADD/WO children would exhibit a greater number of soft signs than ADD/H children who in turn would show more soft signs than normal children. Participants were 31 children ranging in age from 72 to 144 months. The SNAP checklist (Pelham & Murphy, 1981) was used in arriving at an experimental diagnosis. No differences were found between the ADD/WO and normal groups. The ADD/H group exhibited more soft signs than the normal group at all ages and more than the ADD/WO group above 96 months of age.

Journal Article↗

PubMed1991

Corpus callosum morphology in attention deficit-hyperactivity disorder: morphometric analysis of MRI.

Although behavioral evidence provides support for the notion that attention deficit-hyperactivity disorder (ADHD) is related to central nervous system dysfunction, there is little direct evidence to reveal which neurometabolic systems or brain structures are involved. Recent magnetic resonance imaging (MRI) studies suggest that, compared to nondisabled controls, ADHD children may have a smaller right frontal region. Morphometric analysis of MRI scans was used in this exploratory study to determine whether correlated regional variation might exist in the corpus callosum of children with ADHD. While all MRI scans were judged to be clinically normal, morphometric analysis revealed that, compared to nondisabled controls, ADHD children had a smaller corpus callosum, particularly in the region of the genu and splenium, and in the area just anterior to the splenium. Interhemispheric fibers in these regions interconnect the left and right frontal, occipital, parietal, and posterior temporal regions. These results suggest that subtle differences may exist in the brains of children with ADHD and that deviations in normal corticogenesis may underlie the behavioral manifestations of this disorder.

Attention Deficit Disorder with Hyperactivity↗

PubMed1991

Attention deficit disorder without hyperactivity: a distinct behavioral and neurocognitive syndrome.

This study examined the issue as to whether or not children carefully diagnosed as having either attention deficit disorder with hyperactivity (ADDH) or without hyperactivity (ADDnoH) could be distinguished on selected cognitive, academic, rapid naming, and behavioral measures. Employing a previously validated multimodal, multi-informant diagnostic process that results in reliable clinical diagnoses, 10 ADDH and 10 ADDnoH children were examined. While no significant differences in cognitive ability were noted between groups, significant underachievement was found in the children diagnosed as ADDnoH, particularly in mathematics achievement. The ADDnoH children were also significantly slower on rapid naming tasks than the ADDH children. Further, 60% of the ADDnoH children had a codiagnosis of a developmental reading or arithmetic disorder while none of the ADDH children received such a codiagnosis. Conversely, 40% of the ADDH children had a codiagnosis of conduct disorder and were rated by their parent as significantly more motorically active, impulsive, and deviant in the demonstration of age-appropriate social skills. These findings are discussed as they relate to the notion that children with attention deficit disorder may suffer from a right hemispheric syndrome.

Attention Deficit Disorder with Hyperactivity↗

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

The effects of head and eye turns on the right ear advantage in dichotic listening.

The aim of the present experiment was to investigate the effects of head and eye turns on the ear advantage in dichotic listening (DL) to CV-syllables. Since head and eye turns also mean focusing attention to either the left or right side in space, a second aim was to evaluate recent arguments that ear advantages seen in DL are caused by the perceived position in space of the sound source. Forty right-handed females had 36 trials of CV-syllables under four different instructions. One group (n = 20) was instructed to turn their head (but not their eyes) to the right, the left, or straight ahead during stimulus presentations. The fourth condition was a standard (no instruction) condition. A second group (n = 20) had the same instructions but were told to turn their eyes instead of their heads. Conditions were pseudo-counterbalanced across subjects. Consistent with other studies, results showed a right ear advantage (REA) in both groups during all conditions. However, the REA was largest for the standard condition. Also, more subjects showed a REA during the standard condition, and especially compared to the turn-right condition. It is concluded that dichotic performance is not caused by selective attention to either side in space, and that lateral turns of the head and the eyes contralateral to the left hemisphere have an inhibitory (if anything) effect on the REA.

Adult↗

PubMed1990

Right hemispheric dysfunction in nonverbal learning disabilities: social, academic, and adaptive functioning in adults and children.

This review addresses recent research on social and nonverbal learning disabilities. Involvement of right hemispheric dysfunction in these disabilities has been hypothesized, as studies with adults have suggested that documented right hemisphere damage may lead to deficits in social skills, prosody, spatial orientation, problem solving, and recognition of nonverbal cues. Studies of children purported to evidence nonverbal learning disabilities are reviewed and compared with the results from studies of adults with right hemisphere damage. Specific subtypes of nonverbal learning disabilities are reviewed, including the nonverbal perceptual-organization-output subtype, Asperger's Syndrome, Developmental Gerstmann Syndrome, left hemisyndrome, right hemisphere syndrome, and right parietal lobe syndrome. Finally, implications and future research needs are addressed. The need for a diagnostic nosology and improved and validated intervention techniques is stressed as is early identification of these types of specific nonverbal learning disabilities.

Adaptation, Psychological↗

PubMed1990

A WAIS-R marker for accelerated aging and dementia, Alzheimer's type? Base rates of the Fuld formula in the WAIS-R standardization sample.

Recent reports have provided evidence that a WAIS-R marker for dementia of the Alzheimer's type (DAT) may have value in differential clinical diagnosis. Using the Fuld (1984) formula, this study investigated the prevalence of the WAIS-R marker in the WAIS-R standardization sample (N = 1,880), whose members range in age from 16 to 74 years. The results from the WAIS-R sample suggest no significant age differences in the occurrence of this marker when age-corrected scaled scores are employed. Across age, the occurrence of this marker is about 6.2%. Although there were no significant effects according to race, there were significant sex (males = 7.34%; females = 5.11%) and education effects. For individuals aged 65-74 with some post high school education, the base rate was about 14%. These findings are discussed as they relate to the potential clinical usefulness of this marker in the differential diagnosis of DAT.

Adolescent↗

PubMed1990

Frontal lobe functioning in conduct disordered juveniles: preliminary findings.

This investigation assessed the hypothesis that conduct disordered juveniles may suffer from a maturational lag in the development of behaviors believed associated with the frontal cortex. Twenty conduct disorder (CD) juveniles and 20 normal comparison subjects were compared on nine Lurian tasks that measure behavior attributed to frontal lobe functioning. A three-way ANOVA, with gender, race, and group as factors of interest, revealed significant differences on the verbal conflict task, verbal retroactive inhibition task, and on a measure of receptive vocabulary. Using receptive vocabulary as a covariate, an ANCOVA showed no significant differences between the groups on any of the tasks. These findings appear to support the potential impact that language dysfunction can have in the development of disinhibitory behavior. Other interpretations of the findings are presented.

Journal Article↗

PubMed1990

Do neurocognitive measures differentiate Attention Deficit Disorder (ADD) with and without hyperactivity?

Recent behavioral and neuropharmacological evidence suggests that the differentiation of children with Attention Deficit Disorder with (ADD/H) and without hyperactivity (ADD/WO) may reflect an appropriate nosological distinction. There is also evidence that attention-regulatory mechanisms possibly associated with anterior-posterior processes may be independently implicated in these children. To test this hypothesis, 100 clinic-referred children were reliably diagnosed as ADD/H (n = 48). ADD/WO (n = 26) and as having an internalizing disorder (n = 26) for inclusion as a clinic-control (CC) group. An analysis of covariance using Full-Scale IQ, chronological age, and the number of conduct-disorder symptoms provided little support for such a behavioral distinction using selected WISC-R, Luria-Nebraska-Children's Revision, and reaction-time variables. Alternative conceptualizations, possibly reflecting deficient right-hemispheric processes in ADD/H, may provide more productive avenues for research in distinguishing deficient neurocognitive processes in subtypes of ADD.

Journal Article↗

PubMed1989

Neuropsychological test performance and the attention deficit disorders: clinical utility of the Luria-Nebraska Neuropsychological Battery-Children's Revision.

The Luria-Nebraska Neuropsychological Battery-Children's Revision (LNNB-CR) was administered to 54 clinic-referred children aged 8-12 years. Children reliably diagnosed as attention deficit disorder with hyperactivity were compared with children diagnosed as attention deficit disorder without hyperactivity and with a clinic control group diagnosed with internalizing disorders. Both attention deficit disorder groups were lower than the control group in verbal and Full Scale IQ scores but did not differ from one another. The groups did not differ significantly on any of the LNNB-CR clinical scales, on the right or left hemisphere scores, or on the pathognomonic score using analyses of variance or analyses of covariance with both Full Scale IQ and age as covariates. These findings failed to support the hypothesis that attention deficit disorder, either with or without hyperactivity, is associated with neuropsychological dysfunction as measured by the LNNB-CR.

Attention↗

PubMed1989

Dyslexia and brain morphology.

Although the neurological basis of dyslexia has long been assumed, little direct evidence documents a relation between deviations in brain morphology and behavioral correlates of dyslexia. This article reviews two sources of evidence. Results of CT/MRI studies suggest that in the brains of dyslexics there is an increased incidence of symmetry in the region of the planum temporale and parietooccipital cortex that may be associated with language delay and handedness. Postmortem/cytoarchitectonic studies document symmetry of the plana, provide evidence of thalamic involvement, and chart widely distributed focal dysplasias preferentially involving the left frontal, left temporal, and right frontal regions. Methodological deficiencies characterize this literature, however, particularly regarding the diagnosis of dyslexia, appraisal of handedness and neurolinguistic deficits, and a failure to provide evidence that this pattern of involvement is unique to the dyslexic syndrome. These findings are discussed as they relate to neurobiological theory.

Brain↗

PubMed1989

Dyslexia and neurodevelopmental pathology: relationships to cognition, intelligence, and reading skill acquisition.

This article addresses the neuroimaging (CT/MRI), electrophysiological (ERP/EEG), and postmortem evidence as to the neurological basis of dyslexia and discusses why these sources of evidence yield what appear to be inconsistent findings. It is concluded that what appear to be inconsistencies may relate in part to limitations of these investigative technologies. Then, important correlates of reading ability and disability are discussed in a developmental-neuropsychological context, and recommendations are made for research serving to further integrate cognitive and neurological paradigms. Of particular importance, inconsistencies between the results revealed through neuroimaging, electrophysiological, and postmortem studies, on the one hand, and neurolinguistic theory, on the other, must be addressed. Articulating the neurometabolic role-and particularly the nature of the behavioral correlates of the thalamus, supplementary motor area, and frontal cortex-in regard to bihemispheric mechanisms related to reading in developmental dyslexia should be a priority in future research.

Cognition Disorders↗

PubMed1989

Attention deficit disorder with and without hyperactivity: reaction time and speed of cognitive processing.

This study addressed the issue as to whether children reliably diagnosed as attention deficit disordered with hyperactivity (ADD/H) and without hyperactivity (ADD/WO) differed significantly from each other and a clinic control (CC) population on speed and efficiency of cognitive processing. From an outpatient clinic population, 43 ADD/H and 22 ADD/WO children were examined. An analysis of mean reaction time and speeded classification task performance revealed significant group effects on both mean reaction time and on a measure of within-subject variability. ADD/H children performed significantly more slowly and variably than the CC children on several of the speeded classification tasks. However, the ADD/WO group was not distinguished on any measure. Thus, while children may be reliably diagnosed as ADD/H or ADD/WO using behavioral measures, it would appear that they cannot be distinguished on these neurocognitive tasks. Issues related to childhood psychopathology and the neuropsychological basis of ADD/H are discussed.

Age Factors↗

PubMed1989

Regional cerebral blood flow (rCBF) in normal readers: bilateral activation with narrative text.

Based on recent evidence that suggests a more active participation of the right cerebral hemisphere in reading, this exploratory study examined changes in regional cerebral blood flow (rCBF) in three normal subjects during the reading of controlled narrative text. Narrative text presumably activates all neurocognitive processes important in reading including the semantic, pragmatic, emotional, and imagery components. Because of the small number of subjects, percentage change over a baseline at rest condition in rCBF during reading was compared to test/retest variability in control subjects. Effect size was also considered. The results indicated statistically significant bilateral central posterior activation during reading. These findings are consistent with an evolving model of bilateral language representation in which subcortical structures and right hemispheric systems are functionally and anatomically tied to the dominant left hemispheric language centers.

Journal Article↗