Attentional control systems and the Attention Deficit Disorders (ADD)

Dysfunction of right-hemisphere attentional networks in attention deficit hyperactivity disorder

Although differential right-hemisphere dysfunction has been implicated in attention deficit hyperactivity disorder (ADHD) for more than 15 years, this relation remains controversial. Neuroimaging studies suggest asymmetric dysfunction, but neuropsychological evidence in support of this is rather inconsistent. This study examined attentional asymmetry in ADHD adults with a psychophysical extinction task. The interference from right- or left-hemifield distractors with contralateral orientation sensitivity was determined. In a previous study using this paradigm, right brain-damaged patients with left neglect displayed asymmetric distractor interference, meaning a significant interference from a right distractor with left-hemifield orientation sensitivity but no interference from a left distractor with right-hemifield orientation sensitivity. A similar but less pronounced asymmetry was observed in a group of ADHD adults (n = 16). These results indicate dysfunction of right-hemisphere attentional circuits in ADHD.

Right hemisphere dysfunction in ADHD: visual hemispatial inattention and clinical subtype

The relationship between right hemisphere dysfunction and attention-deficit/hyperactivity disorder (ADHD) remains controversial. We administered a random letter cancellation test to 58 carefully selected adult patients meeting DSM-IV criteria for ADHD and 29 age- and education-matched controls. Patients with ADHD had a higher mean omission rate on the left side than the controls, and a greater percentage of ADHD patients than controls made more omissions on the left than on the right (L > R errors). ADHD patients who made L > R errors had lower performance IQ scores than ADHD patients who did not make L > R errors. However, ADHD patients who made L > R errors did not differ from ADHD patients who did not make L > R errors in ADHD subtype, medication response, or neuropsychological measures of attention, executive function, verbal memory, nonverbal memory, or academic achievement. Patients without a family history of ADHD were more likely to make L > R errors than patients with a family history of ADHD. This study provides support for the concept of right hemisphere dysfunction in a subset of patients with ADHD. However, ADHD patients who make L > R errors do not appear to represent a distinct clinical subgroup in terms of medication response, ADHD subtype, or neuropsychological test performance.

Executive dysfunctions in children with attention deficit hyperactivity disorder

One hundred and twenty-four male children ranging in age from seven to 12 years-old were selected. The sample was divided into two groups: (1) sixty-two with attention deficit hyperactivity disorder (ADHD) children; and (2) sixty-two normal matched controls (N-ADHD). Three tests were individually administered: (1) Wisconsin Card Sorting Test (WCST); (2) Verbal fluency and semantics (animals and fruits); and, (3) Picture Arrangement subtest of the WISC-R. For all the test scores, statistically significant differences were found between both ADHD and N-ADHD groups. Two separate factor analyses were performed, using the normal and ADHD groups. Four factors were found for the N-ADHD group, which accounted for 85.7% of the variance. The factor structure presented some similarities in both groups: Factor 2, 3 and 4 in the control group corresponded to factors 1, 2 and 3 in the ADHD group. Nonetheless, in the ADHD group Factor 1 (Abstraction and Flexibility Factor) was absent. Results are interpreted as supporting the hypothesis of executive dysfunction in children with ADHD.

Evaluating medication response in ADHD: cognitive, behavioral, and single-subject methodology

Although evidence supports the use of double-blind placebo medication trials to evaluate methylphenidate (MPH) effects on the core behavioral symptoms of attention-deficit/hyperactivity disorder (ADHD), few studies have demonstrated their utility in examining MPH effects on the cognitive deficits associated with ADHD. This article presents a technique for evaluating behavioral and cognitive dose-response relationships at the single-subject level of analysis. Case study results and multivariate analyses suggest that systematic evaluation of behavioral and cognitive MPH dose-response relationships could lead to more accurate MPH titration and greater long-term multimodal treatment efficacy.

Attentional skills following traumatic brain injury in childhood: a componential analysis

Recent research has documented residual deficits in attention following traumatic brain injury in childhood. The present study aimed to investigate whether such deficits are global, or affect specific components of attention differentially. Four attentional domains were examined using a newly developed test of attention, the Test of Everyday Attention for Children: sustained attention, focussed attention, divided attention, and response inhibition. Eighteen children with a history of traumatic brain injury, aged between 8 and 14 years, and 18 non-injured matched controls participated in the study. Results indicated that attentional skills may be differentially impaired after TBI, with children who have sustained moderate-to-severe TBI exhibiting significant deficits for sustained and divided attention, and response inhibition, but relatively intact focussed attention.

Thyroid hormone and attention in school-age children with congenital hypothyroidism

The relationship between attention and thyroid hormone was examined using a retrospective database of 85 7-year-old children with congenital hypothyroidism who received psychological evaluations and thyroid function tests on the same day. Four unique subgroups with different levels of thyroxine and thyrotropin were compared on psychological tasks and measures of attention. Children with high levels of both hormones were found to be significantly more distractable on an index of cognitive attention but were reportedly less hyperactive. Level of thyroxine accounted for over 10% of the variance in attention.

External Validity of Attention Deficit Disorder without Hyperactivity: A Review of the Evidence

The research evidence for the external validity of Attention Deficit Disorder without Hyperactivity as separate from Attention Deficit Disorder with Hyperactivity is examined. The history of the association between these two diagnoses is summarized, as is the clinical significance of examining this issue. Research on the behavioral characteristics, family history, psychiatric comorbidity, test performance, treatment response, physiological and neuroanatomical correlates of these two groups is reviewed. It is concluded that the evidence supporting the external validity of Attention Deficit Disorder without Hyperactivity as a distinct clinical entity is lacking, although psychophysiological research is emerging as a promising area of research in this regard.

Attention-deficit hyperactivity disorder: magnetic resonance imaging morphometric analysis of the corpus callosum

OBJECTIVE

The following study seeks to document possible differences in corpus callosal area and shape between children with attention-deficit hyperactivity disorder (ADHD) and controls.

METHODS

Fifteen carefully diagnosed right-handed male subjects with ADHD with overactivity symptomatology were compared to 15 right-handed male control subjects. The corpus callosum was divided into seven areas on the midsagittal slice of a magnetic resonance image with shape analysis also conducted.

RESULTS

An exploratory shape analysis showed no significant differences in shape between the groups. No group differences were found in the area, length, or anterior regions of the corpus callosum. The ADHD subjects were found to have significantly smaller posterior corpus callosum regions than the control group, with the splenium accounting for most of the variance between the groups.

CONCLUSIONS

The splenial area of the corpus callosum is smaller in children with ADHD than in a sample of normally developing children. These smaller areas may relate to commonly seen sustained attention deficits which in turn negatively impact on the development of more advanced levels of attention such as self-regulation. Further study of the regions surrounding the splenial area is suggested to determine whether they are correlated in size to the smaller corpus callosum.

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.