George W. Hynd

Neuropsychological development of behavior attributed to frontal lobe functioning in children

There has long been speculation as to the development of behaviors attributed to frontal lobe functioning in children. Controversy exists as to when behaviors attributed to frontal lobe functioning become fully developed. This study examined the performance of normal male and female children at four age levels between 6 and 12 years of age. Performance on verbal and nonverbal proactive and retroactive inhibition, verbal and nonverbal conflict, and two perseve‐ration tasks was assessed. The results suggested that in children, the development of behaviors associated with frontal lobe functioning is a multistage process. The greatest period of development appeared to occur at the 6‐ and 8‐year‐old levels. By the age of 10, the ability to inhibit attention to irrelevant stimuli and perseveratory responses was fairly complete, with mastery evident by age 12.

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. (J Child Neurol 1993;8:339-347).

The Role of the Corpus Callosum in Interhemispheric Transfer of Information: Excitation or Inhibition?

The corpus callosum is the major neural pathway that connects homologous cortical areas of the two cerebral hemispheres. The nature of how that interhemispheric connection is manifested is the topic of this review; specifically, does the corpus callosum serve to communicate an inhibitory or excitatory influence on the contralateral hemisphere? Several studies take the position that the corpus callosum provides the pathway through which a hemisphere or cortical area can inhibit the other hemisphere or homologous cortical area in order to facilitate optimal functional capacity. Other studies suggest that the corpus callosum integrates information across cerebral hemispheres and thus serves an excitatory function in interhemispheric communication. This review examines these two contrasting theories of interhemispheric communication. Studies of callosotomies, callosal agenesis, language disorders, theories of lateralization and hemispheric asymmetry, and comparative research are critically considered. The available research, no matter how limited, primarily supports the notion that the corpus callosum serves a predominantly excitatory function. There is evidence, however, to support both theories and the possibility remains that the corpus callosum can serve both an inhibitory and excitatory influence on the contralateral hemisphere.

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.

Psychopathology in the Parents of Children with Conduct Disorder and Hyperactivity

Abstract The biological parents of 86 outpatient children aged 6 to 1 3 years were assessed using a structured diagnostic interview. Both mothers and fathers of children with Conduct Disorder (CD) (N = 37) were more likely to exhibit Antisocial Personality Disorder, and fathers were more likely to abuse substances. CD mothers exhibited more depression and the triad of Antisocial Personality Disorder. Substance Abuse, or Somatization Disorder. In contrast. Attention Deficit Disorder with Hyperactivity (ADD/H) (N = 18) was not associated with any parental disorder. However, fathers of children with both CD and ADD/H, which is associated with greater aggression and persistent law-breaking in children than CD alone, were markedly more likely to have a history of aggression, arrest, and imprisonment. These results confirm findings that CD is linked to parental psychopathology but ADD/ H is not. When CD and ADD/H co-occur, however, there is markedly more aggression and illegal activity in both fathers and children. J. Am. Acad. Child. Adolesc Psychiatry , 1988, 27. 2:163–170.

Dimensions and types of attention deficit disorder

Abstract DSM-III-R provides a unidimensional definition of attention deficit-hyperactivity disorder (ADHD), based on the assumption that inattention, impulsivity, and motor hyperactivity are unitary aspects of the same dimension. The definition of undifferentiated attention deficit disorder (UADD), however, contradicts this assumption by treating inattention as a separate dimension. The present study evaluated these assumptions empirically. A cluster analysis of three factors derived from factor analyses of teacher ratings of ADD symptoms and a broader list of ADD symptoms produced three distinct clusters: patients without ADD, those with both inattention and hyperactivity, and a group that exhibited inattention and sluggish tempo but not hyperactivity. The association was very strong between the empirically derived clusters and clinical DSM-III diagnoses of ADD with and without hyperactivity. These findings do not support the DSM-III-R unidimensional definition of ADHD.

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.

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, Aspergers 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.

Validity of DSM-IV ADHD Predominantly Inattentive and Combined Types: Relationship to Previous DSM Diagnoses/Subtype Differences

UNLABELLED Since 1980, three different diagnostic nomenclatures have been published regarding attention-deficit hyperactivity disorder (ADHD). These changing conceptualizations and diagnostic criteria have generated considerable confusion. OBJECTIVE To examine the multidimensional DSM-IV ADHD criteria in relation to how children and adolescents with a previous DSM-III ADD diagnosis or a DSM-III-R ADHD diagnosis are diagnosed according to DSM-IV criteria. METHOD Children whose original diagnoses were according to DSM-III and DSM-III-R criteria received retrospective diagnoses according to DSM-IV criteria. RESULTS Predominantly inattentive (n = 30) and combined types (n = 26) were compared on their previous DSM-III and DSM-III-R diagnoses and on demographic, behavioral, cognitive, and comorbidity variables. Predominantly inattentive and combined type diagnoses corresponded with DSM-III ADD/WO and ADD/H diagnoses, respectively. The DSM-III-R ADHD diagnosis did not correspond with either DSM-IV subtype. Children with the combined type diagnosis had more externalizing codiagnoses, and their parents reported more externalizing, delinquent, and aggressive behaviors. Children with the predominantly inattentive type had more math learning disability codiagnoses. CONCLUSION Results support a multidimensional conceptualization of ADHD. There exists close correspondence between the DSM-III ADD/WO type and the DSM-IV predominantly inattentive type and between the DSM-III ADD/H type and the DSM-IV combined type.

Rapid Naming Deficits in Children and Adolescents with Reading Disabilities and Attention Deficit Hyperactivity Disorder

Seventy-one children in three groups (reading disabilities, ADHD without reading disabilities, and normal controls) were compared on their ability to rapidly name colors, letters, numbers, and objects (RAN Tasks) and alternating letters/numbers and letters/numbers/colors (RAS tasks). Children with reading disabilities were found to be slower on letter- and number-naming tasks and made more errors on all tasks than controls or children with ADHD. There was an age effect for the RAN/RAS tasks, with younger children with reading disabilities performing more poorly on all tasks, while the older children with reading disabilities showed poorer performance only on the letter- and number-naming tasks.