Corpus callosum may be similar in children with ADHD and siblings of children with ADHD

Mixed-amphetamine salts expectancies among college students: Is stimulant induced cognitive enhancement a placebo effect?

INTRODUCTION

Non-medical use of prescription stimulants for cognitive enhancement in college students is increasing, despite evidence showing little benefit in non-clinical populations. The balanced placebo design (BPD) was used to independently evaluate the pharmacologic versus expectancy effects of mixed amphetamine salts on cognitive performance among a non-clinical sample of college-aged students.

METHOD

Participants were screened and excluded for ADHD and other psychopathologies. A non-clinical sample (N=32) completed four two-hour laboratory sessions and were administered a neurocognitive battery in each session. Medication Assignment (10mg mixed-amphetamine salt (Adderall™) versus placebo) was crossed with Instructional Set (deception versus truth). A within-subjects design was used, such that all participants experienced each of the four conditions of the BPD during one of the four laboratory sessions.

RESULTS

Participants performed no better than chance in identifying whether they received stimulant or placebo (Belief about Medication Assignment; 47% agreement; κ=-0.047, p=0.590). Participants showed improvement on only two of 31 subtests during active medication. Expecting and receiving stimulants was associated with improved cognitive performance. However, expecting placebo was associated with worse cognitive performance, regardless of the type of medication given.

DISCUSSION

This study demonstrated that although non-medical use of stimulants does not enhance cognition, expectancies prominently influence cognitive performance. Participants who believed they received active medication both subjectively rated themselves as performing better and objectively performed better on a minority of subtests, independent of medication state.

Developmental trajectories of the corpus callosum in attention-deficit/hyperactivity disorder

BACKGROUND

It was recently found that the development of typical patterns of prefrontal, but not posterior, cortical asymmetry is disrupted in right-handed youth with attention-deficit/hyperactivity disorder (ADHD). Using longitudinal data, we tested the hypothesis that there would be a congruent disruption in the growth of the anterior corpus callosum, which contains white matter tracts connecting prefrontal cortical regions.

METHODS

Areas of five subregions of the corpus callosum were quantified using a semiautomated method from 828 neuroanatomic magnetic resonance scans acquired from 236 children and adolescents with ADHD (429 scans) and 230 typically developing youth (399 scans), most of whom had repeated neuroimaging. Growth rates of each diagnostic group were defined using mixed-model linear regression.

RESULTS

Right-handed participants with ADHD showed a significantly higher rate of growth in the anterior-most region of the corpus callosum (estimated annual increase in area of .97%, SEM .12%) than their typically developing peers (annual increase in area of .32% SEM .13%; t = 3.64, p = .0003). No significant diagnostic differences in growth rates were found in any other regions in right-handed participants, and no significant diagnostic differences were found in non-right-handed participants.

CONCLUSIONS

As hypothesized, we found anomalous growth trajectories in the anterior corpus callosum in ADHD. This disrupted anterior callosal growth may reflect, or even drive, the previously reported disruption in the development of prefrontal cortex asymmetry. The finding documents the dynamic, age-dependent nature of callosal and congruent prefrontal cortical abnormalities characterizing ADHD.

Corpus callosum anatomy in chronically treated and stimulant naïve ADHD

OBJECTIVE

To determine the effect of chronic stimulant treatment on corpus callosum (CC) size in children with ADHD using volumetric and area measurements. Previously published research indicated possible medication effects on specific areas of the CC.

METHOD

Measurements of the CC from anatomical MRIs were obtained from children aged 9-16 in three diagnostic groups (a) chronically treated ADHD, (b) stimulant-naïve ADHD, and (c) typically developing children.

RESULTS

The three groups did not differ in overall CC volume. Additional analyses found differences in the area of the splenium, with the treatment-naïve group exhibiting the smallest area.

CONCLUSIONS

Previously reported reductions of CC size in ADHD samples do not appear to be a result of chronic stimulant treatment. The current study suggested a trend toward normalization of splenium size for participants treated with stimulant medication.

Imaging genetics in ADHD: a focus on cognitive control

This paper evaluates neuroimaging of cognitive control as an endophenotype for investigating the role of dopamine genes in ADHD. First, this paper reviews both data-driven and theory-driven approaches from genetics and neuroimaging. Several viable candidate genes have been implicated in ADHD, including the dopamine DRD4 and DAT1 genes. Neuroimaging studies have resulted in a good understanding of the neurobiological basis of deficits in cognitive control in this disorder. Second, this paper discusses imaging genetics in ADHD. Papers to date have taken one of two approaches: whereas early papers investigated the effects of one or two candidate genes on many brain areas, later papers constrained regions of interest by gene expression patterns. These papers have largely focused on cognitive control and the dopamine circuits involved in this ability. The results show that neuroimaging of cognitive control is useful as an endophenotype in investigating dopamine gene effects in ADHD. Other avenues of investigation are suggested by a combination of data- and theory-driven approaches in both genetics and neuroimaging.

Diffusion tensor quantification of the human midsagittal corpus callosum subdivisions across the lifespan

The midsagittal corpus callosum (CC) cross-sectional area subdivisions have been used as early and sensitive markers of human brain white matter connectivity, development, natural aging and disease. Despite the simplicity and conspicuity of the appearance of the CC on anatomical magnetic resonance imaging (MRI), the published quantitative MRI literature on its regional sex and age trajectories are contradictory. The availability of noninvasive quantitative methods to assess the CC regions across the human lifespan would help clarify its contribution to behavior and cognition. In this report, we extended the utility of a recently described semi-automated diffusion tensor imaging (DTI) tissue segmentation method to utilize the high orientation contrast of the CC on DTI. Using optimized DTI methods on a cohort of 121 right-handed children and adults aged 6-68 years, we examined the CC areas and corresponding DTI metrics of the different functionally specialized sectors of the CC. Both the area and fractional anisotropy metrics followed inverted U-shaped curves, while the mean and radial diffusivities followed U-curves reflecting white matter progressive and regressive myelination dynamics that continue into young adulthood.

Lower extremity response time performance in boys with ADHD

OBJECTIVE

Children with ADHD have been labeled as "uncoordinated" and "inefficient movers"; however, a paucity of research has systematically examined "stimulant-free" motor processing in this population.

METHOD

In the present investigation, the authors employ a cross-lateral integration task to assess the attainment of a motor milestone in a corpus of 16 adolescents with ADHD acutely removed from their daily medication routine (methylphenidate) and 19 age-matched peers. Participants perform a choice response time task involving the lower extremity to targets located at midline and in ipsilateral and contralateral space.

RESULTS/CONCLUSION

This investigation finds that children with ADHD have slower lower extremity reaction and movement times compared to controls, and all preadolescent children demonstrate an inhibition in processing movements that require crossing the midline of the body.

Structural brain imaging of attention-deficit/hyperactivity disorder

Many investigators have hypothesized that attention-deficit/hyperactivity disorder (ADHD) involves structural and functional brain abnormalities in frontal-striatal circuitry. Although our review suggests that there is substantial support for this hypothesis, a growing literature demonstrates widespread abnormalities affecting other cortical regions and the cerebellum. Because there is only one report studying adults with ADHD, this summary is based on children. A key limitation of the literature is that most of the studies until recently have been underpowered, using samples of fewer than 20 subjects per group. Nevertheless, these studies are largely consistent with the most comprehensive and definitive study (Castellanos et al 2002). Moreover, studies differ in the degree to which they address the influence of medications, comorbidities, or gender, and most have not addressed potentially important sources of heterogeneity such as family history of ADHD, subtype, or perinatal complications. Despite these limitations, a relatively consistent picture has emerged. The most replicated alterations in ADHD in childhood include significantly smaller volumes in the dorsolateral prefrontal cortex, caudate, pallidum, corpus callosum, and cerebellum. These results suggest that the brain is altered in a more widespread manner than has been previously hypothesized. Developmental studies are needed to address the evolution of this brain disorder into adulthood.

A review of the biological bases of ADHD: what have we learned from imaging studies?

Attention Deficit Hyperactivity Disorder (ADHD) is a common and impairing neuropsychiatric disorder with onset at preschool age. Although a significant amount of progress has been made investigating the neurobiology of this disorder, its precise etiology still remains unclear. Converging evidence from studies of the neuropharmacology, genetics, neuropsychology, and neuroimaging of ADHD imply the involvement of fronto-striatal circuitry in ADHD. However, while it does appear that poor inhibitory control and the deficits in fronto-striatal circuitry associated with it are central, there is evidence to suggest that more posterior cerebral areas are also implicated in this disorder. Anatomical studies suggest widespread reductions in volume throughout the cerebrum and cerebellum, while functional imaging studies suggest that affected individuals activate more diffuse areas than controls during the performance of cognitive tasks. The future impact of new MR imaging methodologies on the field is discussed.

The dynamic approach to neurodevelopmental psychiatric disorders: use of fMRI combined with neuropsychology to elucidate the dynamics of psychiatric disorders, exemplified in ADHD and schizophrenia

The paper discusses the application of fMRI in combination with neuropsychology to neurodevelopmental psychiatric disorders, exemplified on the case of attention deficit hyperactivity disorder (ADHD) in comparison with schizophrenia. The view is presented that ADHD, rather than being a compound of unrelated co-existing deficits, is a pervasive disorder of impulsiveness, which manifests at the motor, emotional, social and cognitive domain. Neuropsychology needs to refine the psychological measurements of these impulsivity symptoms and, in combination with fMRI, provide new insights into the interrelationship between brain and dysfunction and its bi-directional causalities. The suitability of the dynamic technique of functional MRI to assess the dynamic nature of developmental neuropsychiatric disorders is discussed. Brain activation can inform about strategy and compensatory mechanisms at a neuroanatomical level, which are not observable at a psychological level, providing insight into the underlying neurocognitive mechanisms of psychiatric disorders. Data are presented and discussed on opposing neurocognitive activation patterns for patients with ADHD and those with schizophrenia while performing a stop task. Comparisons between patient groups will be essential to address the specificity of neurocognitive mechanisms corresponding to specific neurodevelopmental psychiatric disorders.

Incoherence of neuroimaging studies of attention deficit/hyperactivity disorder

Neuroimaging studies have been conducted with increasing frequency in recent years in attempts to identify structural and functional abnormalities in the brains of persons with attention deficit/hyperactivity disorder. Although the results of these studies are frequently cited in support of a biologic etiology for this disorder, inconsistencies among studies raise questions about the reliability of the findings. The present review shows that no specific abnormality in brain structure or function has been convincingly demonstrated by neuroimaging studies. Implications regarding stimulant treatment for attention deficit/hyperactivity disorder are discussed.