Development of the human corpus callosum during childhood and adolescence: a longitudinal MRI study

Emotional and cognitive changes during adolescence

Adolescence is a critical period for maturation of neurobiological processes that underlie higher cognitive functions and social and emotional behavior. Recent studies have applied new advances in magnetic resonance imaging to increase understanding of the neurobiological changes that occur during the transition from childhood to early adulthood. Structural imaging data indicate progressive and regressive changes in the relative volumes of specific brain regions, although total brain volume is not significantly altered. The prefrontal cortex matures later than other regions and its development is paralleled by increased abilities in abstract reasoning, attentional shifting, response inhibition and processing speed. Changes in emotional capacity, including improvements in affective modulation and discrimination of emotional cues, are also seen during adolescence. Functional imaging studies using cognitive and affective challenges have shown that frontal cortical networks undergo developmental changes in processing. In summary, brain regions that underlie attention, reward evaluation, affective discrimination, response inhibition and goal-directed behavior undergo structural and functional re-organization throughout late childhood and early adulthood. Evidence from recent imaging studies supports a model by which the frontal cortex adopts an increasingly regulatory role. These neurobiological changes are believed to contribute, in part, to the range in cognitive and affective behavior seen during adolescence.

Traumatic stress: effects on the brain

Brain areas implicated in the stress response include the amygdala, hippocampus, and prefrontal cortex. Traumatic stress can be associated with lasting changes in these brain areas. Traumatic stress is associated with increased cortisol and norepinephrine responses to subsequent stressors. Antidepressants have effets on the hippocampus that counteract the effects of stress. Findings from animal studies have been extended to patients with post-traumatic stress disorder (PTSD) showing smaller hippocampal and anterior cingulate volumes, increased amygdala function, and decreased medial prefrontal/anterior cingulate function. In addition, patients with PTSD show increased cortisol and norepinephrine responses to stress. Treatments that are efficacious for PTSD show a promotion of neurogenesis in animal studies, as well as promotion of memory and increased hippocampal volume in PTSD.

Quantitative diffusion tensor tractography of association and projection fibers in normally developing children and adolescents

Whole-brain diffusion tensor tractography (DTT) at high signal-to-noise ratio and angular and spatial resolutions were utilized to study the effects of age, sex differences, and lateral asymmetries of 6 white matter pathways (arcuate fasciculus [AF], inferior longitudinal fasciculus, inferior fronto-occipital fasciculus [IFOF], uncinate fasciculus [UF], corticospinal tract [CST], and somatosensory pathway [SS]) in 31 right-handed children (6-17 years). Fractional anisotropy (FA), a measure of the orientational variance in water molecular diffusivity, and the magnitude of water diffusivity (parallel, perpendicular, and mean diffusivity) along the pathways were quantified. Three major patterns of maturation were observed: 1) significant increase in FA with age, accompanied by significant decreases in all 3 diffusivities (e.g., left IFOF); 2) significant decreases in all three diffusivities with age without significant changes in FA (e.g., left CST); and 3) no significant age-related changes in FA or diffusivity (e.g., SS). Sex differences were minimal. Many pathways showed lateral asymmetries. In the right hemisphere, the frontotemporal (FT) segment of AF was not visualized in a substantial (29%) number of participants. FA was higher in the left hemisphere in the FT segment of AF, UF, and CST, whereas it was lower in the frontoparietal segment of AF. This study provides normative data essential for the interpretation of pediatric brain DTT measurements in both health and disease.

Agenesis of the corpus callosum and the establishment of handedness

The goal of this study was to check whether an isolated agenesis of the corpus callosum, detected in utero with ultrasound recording, would impair the early development of unimanual and bimanual handedness. Twelve infants with isolated agenesis of the corpus callosum, either total (TACC) or partial (PACC) were tested for handedness at the end of their first year, and were compared to infants with typical development (TD), matched for age and sex. A majority of infants showed right-handedness at the unimanual grasping tasks, with no significant difference between the TD and ACC groups. When the object was presented to the left, the TACC infants were more likely to grasp the object with their right hand (with or without the left hand) than both the TD and the PACC infants who used mostly the ipsilateral left hand. The only significant difference between TD and ACC infants concerned bimanual coordination, as less ACC infants (especially TACC) succeeded at the bimanual task, compared with TD infants. In addition, the strategy of the former tended to be less right-handed than that of the latter. Our results confirm the role of the CC in bimanual coordination, indicating that the early emergence of bimanual coordination and, if confirmed, bimanual handedness, are likely to be delayed in the absence of corpus callosum, especially if agenesis is total. They do not support the idea that the CC is necessary for the early onset of handedness.

Diffusion tensor imaging of the corpus callosum in Autism

The corpus callosum is the largest commissural white matter pathway that connects the hemispheres of the human brain. In this study, diffusion tensor imaging (DTI) was performed on subject groups with high-functioning autism and controls matched for age, handedness, IQ, and head size. DTI and volumetric measurements of the total corpus callosum and subregions (genu, body and splenium) were made and compared between groups. The results showed that there were significant differences in volume, fractional anisotropy, mean diffusivity, and radial diffusivity between groups. These group differences appeared to be driven by a subgroup of the autism group that had small corpus callosum volumes, high mean diffusivity, low anisotropy, and increased radial diffusivity. This subgroup had significantly lower performance IQ measures than either the other individuals with autism or the control subjects. Measurements of radial diffusivity also appeared to be correlated with processing speed measured during the performance IQ tests. The subgroup of autism subjects with high mean diffusivity and low fractional anisotropy appeared to cluster with the highest radial diffusivities and slowest processing speeds. These results suggest that the microstructure of the corpus callosum is affected in autism, which may be related to nonverbal cognitive performance.

Diffusion tensor imaging in children with fetal alcohol spectrum disorders

BACKGROUND

Prenatal alcohol exposure, which is associated with macrostructural brain abnormalities, neurocognitive deficits, and behavioral disturbances, is characterized as fetal alcohol syndrome (FAS) in severe cases. The only published study thus far using diffusion tensor imaging (DTI) showed microstructural abnormalities in patients with FAS. The current study investigated whether similar abnormalities are present in less severely affected, prenatally exposed patients who did not display all of the typical FAS physical stigmata.

METHODS

Subjects included 14 children, ages 10 to 13, with fetal alcohol spectrum disorders (FASD) and 13 matched controls. Cases with full-criteria FAS, mental retardation, or microcephaly were excluded. Subjects underwent MRI scans including DTI.

RESULTS

Although cases with microcephaly were excluded, there was a trend toward smaller total cerebral volume in the FASD group (p=0.057, Cohen's d effect size =0.73). Subjects with FASD had greater mean diffusivity (MD) in the isthmus of the corpus callosum than controls (p=0.013, effect size =1.05), suggesting microstructural abnormalities in this region. There were no group differences in 5 other regions of the corpus callosum. Correlations between MD in the isthmus and facial dysmorphology were nonsignificant.

CONCLUSIONS

These results suggest that even relatively mild forms of fetal alcohol exposure may be associated with microstructural abnormalities in the posterior corpus callosum that are detectable with DTI.

Longitudinal brain magnetic resonance imaging study of the alcohol-preferring rat. Part II: effects of voluntary chronic alcohol consumption

BACKGROUND

Tracking the dynamic course of human alcoholism brain pathology can be accomplished only through naturalistic study and without opportunity for experimental manipulation. Development of an animal model of alcohol-induced brain damage, in which animals consume large amounts of alcohol following cycles of alcohol access and deprivation and are examined regularly with neuroimaging methods, would enable hypothesis testing focused on the degree, nature, and factors resulting in alcohol-induced brain damage and the prospects for recovery or relapse.

METHODS

We report the results of longitudinal magnetic resonance imaging (MRI) studies of the effects of free-choice chronic alcohol intake on the brains of 2 cohorts of selectively bred alcohol-preferring (P) rats. In the companion paper, we described the MRI acquisition and analysis methods, delineation of brain regions, and growth patterns in total brain and selective structures of the control rats in the present study. Both cohorts were studied as adults for about 1 year and consumed high doses of alcohol for most of the study duration. The paradigm involved a 3-bottle choice with 0, 15 (or 20%), and 30% (or 40%) alcohol available in several different exposure schemes: continuous exposure, cycles of 2 weeks on followed by 2 weeks off alcohol, and binge drinking in the dark.

RESULTS

Brain structures of the adult P rats in both the alcohol-exposed and the water control conditions showed significant growth, which was attenuated in a few measures in the alcohol-exposed groups. The region with the greatest demonstrable effect was the corpus callosum, measured on midsagittal images.

CONCLUSION

The P rats showed an age-alcohol interaction different from humans, in that normal growth in selective brain regions that continues in adult rats was retarded.

Bimanual interference in children performing a dual motor task

The present study addressed the development of bimanual interference in children performing a dual motor task, in which each hand executes a different task simultaneously. Forty right-handed children (aged 4, 5-6, 7-8 and 9-11years, ten in each age group) were asked to perform a bimanual task in which they had to tap with a pen using the non-preferred hand and simultaneously trace a circle or a square with a pen using the preferred hand as quickly as possible. Tapping and tracing were also performed unimanually. Differences between unimanual and bimanual performance were assessed for number of taps, length of tap trace and mean tracing velocity. It was assumed that with increasing age, better bimanual coordination would result in better performance on the dual task showing less intermanual interference. The results showed that tapping and tracing performance increased with age, unimanually as well as bimanually, consistent with developmental advancement. However, the percentage of intermanual interference due to bimanual performance was not significantly different in the four age groups. Although performing the dual task resulted in mutual intermanual interference, all groups showed a significant effect of tracing shape. More specifically, all age groups showed a larger percentage decrease in tracing velocity when performing the circle compared to the square in the dual task. The present study reveals that children as young as four years are able to coordinate both hands when tapping and tracing bimanually.

Bildgebungsbefunde bei Kindern und Jugendlichen mit ADHS, Tic-Störungen und Zwangserkrankungen

Zusammenfassung: ADHS, Tic-Störung, Tourette-Syndrom und Zwangsstörung sind gekennzeichnet durch Defizite in der Handlungskontrolle und treten überzufällig häufig komorbid auf. Es bestehen Hinweise auf eine gemeinsame neurobiologische Basis. Der folgende Übersichtsartikel fasst Ergebnisse aus Bildgebungsstudien zu diesen Störungen im Kindes- und Jugendalter zusammen, wobei strukturelle und funktionelle Befunde durch Magnetresonanztomographie einen Schwerpunkt einnehmen. Übereinstimmend zeigen sich im Vergleich zu gesunden Kontrollen morphologische Veränderungen im Bereich von Basalganglien und präfrontalem Kortex sowie abnorme Aktivierungen in fronto-striatalen Systemen. Vor allem beim ADHS und Tourette-Syndrom werden präfrontale Abweichungen gefunden, die beim letzteren milder ausgeprägt sind und unter Umständen auf Kompensationsmechanismen zurückzuführen sein könnten. Beim ADHS finden sich zusätzlich kleine, globale morphologische Veränderungen im gesamten Kortex und im Zerebellum, beim Tourette-Syndrom werden zudem Auffälligkeiten im okzipitalen Kortex beschrieben. Bei der Zwangserkrankung bestehen weitere strukturelle und funktionelle Aberrationen im Bereich von Amygdala und Thalamus und zudem orbito-frontale Funktionsveränderungen, die beim ADHS eher im ventralen präfrontalen Kortex zu finden sind. Diese Befunde scheinen insgesamt mit Störungen in kortiko-striato-thalamiko-kortikalen Regelkreisen assoziiert zu sein und u. a. in Verbindung mit Dysfunktionen im Bereich der Inhibition von motorischen Reaktionen, impulsiven Handlungen und unerwünschten Gedanken zu stehen. Generell wird die Aussagekraft und Vergleichbarkeit vieler Studien durch kleine und heterogene Gruppen sowie methodische Unterschiede eingeschränkt.

Gender effects on callosal thickness in scaled and unscaled space

Some empirical data suggest that sexual dimorphisms in callosal morphology exist, but findings are not consistently replicated across laboratories. We applied novel computational surface-based methods to encode callosal thickness at high spatial resolution. We further examined whether callosal thickness and related gender effects are influenced by brain size adjustments achieved through data scaling. Significant gender differences were absent in scaled data, and women showed no regional thickness increases compared with men (in either scaled or unscaled data). In unscaled data, men exhibited significantly greater callosal thickness in a number of regions that may be attributable to larger brain dimensions in men. Alternatively, given their regional specificity, the observed differences in unscaled callosal thickness may contribute to gender-specific cognition and behavior.

Sex differences in the relationship between white matter microstructure and impulsivity in adolescents

Rapid maturational brain changes occur during adolescence--a time associated with risk-taking behaviors and improvements in cognition. The present study examined the relationship between white matter (WM) microstructure, impulsive behavior and response inhibition in female and male adolescents. Twenty-one healthy adolescents underwent diffusion tensor imaging using a 3.0-T magnetic resonance imaging system. Impulse control was assessed using the Bar-On Emotional Quotient Inventory, Youth Version. Response inhibition was assessed using the Stroop Color-Word Interference Test. Fractional anisotropy (FA), a measure of WM coherence, and trace, a measure of overall diffusivity, were determined from voxels manually placed in the midline and in the left and right forward-projecting arms of the genu and the splenium of the corpus callosum. Sex-specific differences were observed for the relationship between FA and impulsive behavior in the right anterior callosum for males and in the splenium for females. Males, compared to females, displayed significantly higher FA in the left WM region. Although trace was not associated with impulse control, trace in the genu (for females) and splenium (males and females) was associated with Stroop performance. Regional differences in trace also were evident, with lower values in the splenium observed than in all other regions. Although the latter significantly improved with age, no sex differences in impulse control or in Stroop performance were detected. The present findings provide supporting evidence for sex-related differences in the development of WM microstructure during adolescence. These data further suggest a neurobiological mechanism underlying some of the emotional and cognitive changes commonly observed in males versus females during the adolescent period.

Neurological abnormalities in young adults born preterm

OBJECTIVE

Individuals born before 33 weeks' gestation (very preterm, VPT) have an increased likelihood of neurological abnormality, impaired cognitive function, and reduced academic performance in childhood. It is currently not known whether neurological signs detected in VPT children persist into adulthood or become attenuated by maturation of the CNS.

METHOD

We assessed 153 VPT individuals and 71 term-born controls at 17-18 years old, using a comprehensive neurological examination. This examination divides neurological signs into primary and integrative domains, the former representing the localising signs of classical neurology, and the latter representing signs requiring integration between different neural networks or systems. Integrative signs are sub-divided into three groups: sensory integration, motor confusion, and sequencing. The VPT individuals have been followed up since birth, and neonatal information is available on them, along with the results of neurological assessment at 4 and 8 years of age and neuropsychological assessment at 18 years of age.

RESULTS

The total neurology score and primary and integrative scores were significantly increased in VPT young adults compared to term-born controls. Within the integrative domain, sensory integration and motor confusion scores were significantly increased in the VPT group, but sequencing was not significantly different between the VPT and term groups. Integrative neurological abnormalities at 18 were strongly associated with reduced IQ but primary abnormalities were not.

CONCLUSIONS

Neurological signs are increased in VPT adults compared to term-born controls, and are strongly associated with reduced neuropsychological function.

Development of the adolescent brain: implications for executive function and social cognition

Adolescence is a time of considerable development at the level of behaviour, cognition and the brain. This article reviews histological and brain imaging studies that have demonstrated specific changes in neural architecture during puberty and adolescence, outlining trajectories of grey and white matter development. The implications of brain development for executive functions and social cognition during puberty and adolescence are discussed. Changes at the level of the brain and cognition may map onto behaviours commonly associated with adolescence. Finally, possible applications for education and social policy are briefly considered.

Brain development and ADHD

Attention-Deficit/Hyperactivity Disorder (ADHD) is characterized by excessive inattention, hyperactivity, and impulsivity, either alone or in combination. Neuropsychological findings suggest that these behaviors result from underlying deficits in response inhibition, delay aversion, and executive functioning which, in turn, are presumed to be linked to dysfunction of frontal-striatal-cerebellar circuits. Over the past decade, magnetic resonance imaging (MRI) has been used to examine anatomic differences in these regions between ADHD and control children. In addition to quantifying differences in total cerebral volume, specific areas of interest have been prefrontal regions, basal ganglia, the corpus callosum, and cerebellum. Differences in gray and white matter have also been examined. The ultimate goal of this research is to determine the underlying neurophysiology of ADHD and how specific phenotypes may be related to alterations in brain structure.

Neurodevelopmental outcomes of infants born prematurely

Long-term follow-up of infants born prematurely is necessary to determine neurodevelopmental outcomes, particularly with the expansion of interest from major disabilities to high prevalence/low severity dysfunctions. Models of pathogenesis include changes due to developmental disruptions and to injury, the magnitude and type of change influenced by the infant's age, and central nervous system recovery and reorganization. Alterations in neurogenesis, migration, myelination, cell death, and synaptogenesis occur even in the absence of insult. Despite increased knowledge regarding these processes, the functional significance of brain abnormalities is unclear. Because of methodologic problems in follow-up studies, it is difficult to characterize outcome definitively. Nonetheless, an acceptable degree of agreement across studies is found with regard to specific neurodevelopmental outcomes: motor/neurologic function, visuomotor integrative skills, IQ, academic achievement, language, executive function, and attention-deficit hyperactivity disorder/behavioral issues. In general, children born prematurely have more problems in these areas than do their normal birth weight counterparts. Suggestions for improved analyses and clarification of outcomes include use of cluster analysis, structural equation modeling, growth curve analysis, developmental epidemiologic approaches, and better control of background variables using risk indexes and factor scores. Better assessment techniques measuring functions documented to be at higher risk of problems are discussed.

The ipsilateral silent period in boys with attention-deficit/hyperactivity disorder

OBJECTIVE

Characterize maturation of transcallosal inhibition (ipsilateral silent period [iSP]) in attention deficit/hyperactivity disorder (ADHD) using transcranial magnetic stimulation (TMS).

BACKGROUND

Maturation of the iSP is related to acquisition of fine motor skills in typically developing children suggesting that dexterous fine motor skills depend upon mature interhemispheric interactions. Since neuromotor maturation is abnormal in boys with ADHD we hypothesized that iSP maturation in these children would be abnormal. We studied iSP maturation in 12 boys with ADHD and 12 age-matched, typically developing boys, 7-13 years of age.

METHODS

Surface electromyographic activity was recorded from right first dorsal interosseus (FDI). During background activation, focal TMS was delivered at maximal stimulator output over the ipsilateral motor cortex.

RESULTS

Maturation of finger speed in boys with ADHD was significantly slower than that in the control group. The iSP latency decreased with age in the control group but not in the ADHD group.

CONCLUSIONS

These findings suggest the presence of a complex relationship between abnormalities of certain interhemispheric interactions (as represented by iSP latency) and delayed maturation of neuromotor skills in boys with ADHD.

SIGNIFICANCE

These data provide preliminary physiologic evidence supporting delayed or abnormal development of interhemispheric interactions in boys with ADHD.

Mapping brain maturation and cognitive development during adolescence

Non-invasive mapping of brain structure and function with magnetic resonance imaging (MRI) has opened up unprecedented opportunities for studying the neural substrates underlying cognitive development. There is an emerging consensus of a continuous increase throughout adolescence in the volume of white matter, both global and local. There is less agreement on the meaning of asynchronous age-related decreases in the volume of grey matter in different cortical regions; these might equally represent loss ("pruning") or gain (intra-cortical myelination) of tissue. Functional MRI studies have so far focused mostly on executive functions, such as working memory and behavioural inhibition, with very few addressing questions regarding the maturation of social cognition. Future directions for research in this area are discussed in the context of processing biological motion and matching perceptions and actions.

Morphometry of the corpus callosum in Chinese children: relationship with gender and academic performance

BACKGROUND

The corpus callosum has been widely studied, but no study has demonstrated whether its size and shape have any relationship with language and calculation performance.

OBJECTIVE

To examine the morphometry of the corpus callosum of normal Chinese children and its relationship with gender and academic performance.

MATERIALS AND METHODS

One hundred primary school children (63 boys, 37 girls; age 6.5-10 years) were randomly selected and the standardized academic performance for each was ascertained. On the mid-sagittal section of a brain MRI, the length, height and total area of the corpus callosum and its thickness at different sites were measured. These were correlated with sex and academic performance.

RESULTS

Apart from the normal average dimension of the different parts of the corpus callosum, thickness at the body-splenium junction in the average-to-good performance group was significantly greater than the below-average performance group in Chinese language (P=0.005), English language (P=0.02) and mathematics (P=0.01). The remainder of the callosal thickness showed no significant relationship with academic performance. There was no significant sex difference in the thickness of any part of the corpus callosum.

CONCLUSIONS

These findings raise the suggestion that language and mathematics proficiency may be related to the morphometry of the fibre connections in the posterior parietal lobes.

Magnetic resonance findings in bipolar disorder

The MR findings reviewed in this article suggest structural, chemical, and functional abnormalities in specific brain regions participating in mood and cognitive regulation, such as the DLPFC, anterior cingulate, amygdala,STG, and corpus callosum in subjects with bipolar disorder. These abnormalities would represent an altered anterior-limbic network disrupting inter- and intrahemispheric communication and underlying the expression of bipolar disorder. Available studies are limited by several confounding variables, such as small and heterogeneous patient samples, differences in clinical and medication status, and cross-sectional design. It is still unclear whether abnormalities in neurodevelopment or neurodegeneration play a major role in the pathophysiology of bipolar disorder. These processes could act together in a unitary model of the disease, with excessive neuronal pruning/apoptosis during childhood and adolescence being responsible for the onset of the disorder and subsequent neurotoxic mechanisms and impaired neuroplasticity and cellular resilience being responsible for further disease progression. Future MR studies should investigate larger samples of first-episode drug-free patients, pediatric patients, subjects at high risk for bipolar disorder, and unaffected family members longitudinally. Such a study population is crucial to examine systematically whether brain changes are present before the appearance of symptoms (eg, maldevelopment) or whether they develop afterwards, as a result of illness course (eg, neurodegeneration). These studies will also be instrumental in minimizing potentially confounding factors commonly found in adult samples, such as the effects of long-term medication, chronicity, and hospitalizations. Juvenile bipolar patients often have a strong family history of bipolar disorder. Future studies could help elucidate the relevance of brain abnormalities as reflections of genetic susceptibility to the disorder. MR studies associated with genetic, post-mortem, and neuropsychologic studies will be valuable in separating state from trait brain abnormalities and in further characterizing the genetic determinants, the neuropathologic underpinnings, and the cognitive disturbances of bipolar disorder.

The psychobiology of neglect

Child neglect, the most prevalent form of child maltreatment, is associated with adverse psychological and educational outcomes. It is hypothesized that these outcomes may be caused by adverse brain development. However, there are very few published cross-sectional studies and no prospective studies that examine the neurodevelopmental consequences of neglect. In this article, the author comprehensively outlines the issues involved in the psychobiological research of child neglect. Pre-clinical and clinical studies will be reviewed. Throughout the article, suggestions for future research opportunities and novel ways to address methodological difficulties inherent in this field of study are offered. The results of recent neuroimaging studies of maltreated children may provide a basis for understanding the early effects of neglect on childhood brain development. The author is comprehensively examining these issues as part of the Federal Child Neglect Consortium.

Development of upper limb proprioceptive accuracy in children and adolescents

This study was designed to determine differences in the proprioceptively guided movements of children (8-10 years) and adolescents (16-18 years). Participants were blindfolded and asked to actively match passively determined target positions of the elbow joint under three matching conditions. Overall, children were less accurate than adolescents in all matching tasks and utilized different kinematic strategies for making the matching movements. Specifically, children made larger absolute errors and utilized matching movements which, compared to adolescents, were of shorter duration and less irregular in terms of their velocity profiles. An assessment of limb asymmetry was also performed revealing a non-dominant arm matching advantage but only for children and only in the task requiring interhemispheric transfer of a memory-based model of limb position. The proprioceptive differences observed in this study are likely the result of experience-driven refinement in the utilization of somatosensory feedback throughout childhood and into adolescence.

White matter development during childhood and adolescence: a cross-sectional diffusion tensor imaging study

Maturation of brain white matter pathways is an important factor in cognitive, behavioral, emotional and motor development during childhood and adolescence. In this study, we investigate white matter maturation as reflected by changes in anisotropy and white matter density with age. Thirty-four children and adolescents aged 6-19 years received diffusion-weighted magnetic resonance imaging scans. Among these, 30 children and adolescents also received high-resolution T1-weighed anatomical scans. A linear regression model was used to correlate fractional anisotropy (FA) values with age on a voxel-by-voxel basis. Within the regions that showed significant FA changes with age, a post hoc analysis was performed to investigate white matter density changes. With increasing age, FA values increased in prefrontal regions, in the internal capsule as well as in basal ganglia and thalamic pathways, the ventral visual pathways, and the corpus callosum. The posterior limb of the internal capsule, intrathalamic connections, and the corpus callosum showed the most significant overlaps between white matter density and FA changes with age. This study demonstrates that during childhood and adolescence, white matter anisotropy changes in brain regions that are important for attention, motor skills, cognitive ability, and memory. This typical developmental trajectory may be altered in individuals with disorders of development, cognition and behavior.

Maturation of white matter is associated with the development of cognitive functions during childhood

In the human brain, myelination of axons continues until early adulthood and is thought to be important for the development of cognitive functions during childhood. We used diffusion tensor MR imaging and calculated fractional anisotropy, an indicator of myelination and axonal thickness, in children aged between 8 and 18 years. Development of working memory capacity was positively correlated with fractional anisotropy in two regions in the left frontal lobe, including a region between the superior frontal and parietal cortices. Reading ability, on the other hand, was only correlated with fractional anisotropy in the left temporal lobe, in the same white matter region where adults with reading disability are known to have lower fractional anisotropy. Both the temporal and the frontal regions were also correlated with age. These results show that maturation of white matter is an important part of brain maturation during childhood, and that maturation of relatively restricted regions of white matter is correlated with development of specific cognitive functions.

Kinematically Specific Interhemispheric Inhibition Operating in the Process of Generation of a Voluntary Movement

Unilateral hand movements are accompanied by a transient decrease in corticospinal (CS) excitability of muscles in the opposite hand. However, the rules that govern this phenomenon are not completely understood. We measured the amplitude of motor evoked potentials (MEP) in the left first dorsal interosseus (FDI) elicited by transcranial magnetic stimulation (TMS) of the primary motor cortex in order to assess CS excitability changes that preceded eight possible combinations of unilateral and bilateral index finger movements with different right hand positions. Left FDI MEP amplitude (MEP(Left FDI)) increased when this muscle acted as an agonist and tended to decrease when it was an antagonist. Additionally, MEP(Left FDI) decreased substantially before right index finger abduction (a movement mediated by the right FDI) when both hands were lying flat (a movement mirroring left index finger abduction) but not when the right hand was turned at 90 degrees or flat with the palm up. Therefore, CS excitability of the resting FDI was differentially modulated depending on the direction of the opposite index finger movement, regardless of muscles engaged in the task. These results indicate that inhibitory interactions preceding unilateral finger movements are determined by movement kinematics possibly to counteract the default production of mirror motions.

Larger corpus callosum size with better motor performance in prematurely born children

The objective of this study is to determine the relation between the size of the corpus callosum (CC) and motor performance in a population-based cohort of preterm children. Preterm born children (n = 221) with a gestational age less than or equal to 32 weeks and/or a birth weight below 1500 g were eligible for this study. At the age of 7 or 8 years, frontal, middle, posterior, and total areas (mm2) of the corpus callosum were measured on true midsagittal MRI. Due to anxiety of 10 children and motion artifacts in 7 other children, 204 MRIs could be assessed in the preterm group (mean GA 29.4 weeks, sd 2.0,mean BW 1200 g, sd 323). The preterm group consisted of 15 children with cerebral palsy (CP) and 189 children without CP. Motor function was established by using the Movement Assessment Battery for Children, and the Developmental Test of Visual Motor Integration was obtained. The same examinations were performed in 21 term born children. The mean total cross-sectional CC area was significantly smaller in preterm born infants compared with their term born controls (338 mm2 versus 422 mm2, P < 0.0001). The preterm children with CP had significantly smaller mean CC areas compared with the preterms who did not develop CP (P < 0.0001-P < 0.002). However, the preterms born without CP also had significantly smaller body, posterior, and total CC areas compared with term born controls (P < 0.0001-P < 0.002). Only the difference in frontal area measurements dilrc) -3.3 mm2/score point (95% CI -4.5, -2.1). The association existed in all parts of the CC but increased in the direction of the posterior part: frontal: lrc -0.8 mm2/score point (-1.2, -0.4), middle: lrc -1.1 mm2/score point (-1.7, -0.5) and posterior: lrc -1.4 mm2/score point (-1.8, -0.9). An association between CC area and its subareas and the standard scores of the VMI was also found. A larger CC was strongly related t o better scores onthe VMI test total area CC: lrc 0.05 score/mm2 (95% CI 0.03, 0.07), frontal: lrc 0.12 score/mm2 (0.05,0.19), middle: lrc 0.10 score/mm2 (0.05, 0.15) and posterior: lrc 0.12 score/mm2 (0.06, 0.18). After adjustment for gestational age, birth weight, and total cerebral area, these associations were still significant. There is a strong association between the size of the corpus callosum (total midsagittal cross area as well as frontal, middle, and posterior area) and motor function in preterm children, investigated at school age. A poorer score on the Movement ABC was related to a smaller CC. A larger CC was strongly associated with better VMI standard scores.

Brain volumes in adult survivors of very low birth weight: a sibling-controlled study

OBJECTIVES

To establish whether adults who were born very low birth weight (VLBW) show altered volumes of certain brain structures.

METHODS

Unmatched case-control study was conducted of 33 individuals from a cohort of VLBW (<1500 g) infants who were born between 1966 and 1977 and 18 of their normal birth weight siblings. Whole brain, gray matter, ventricular, corpus callosum, and hippocampal volumes were measured on structural magnetic resonance imaging scans.

RESULTS

VLBW individuals had a 46% increase in total ventricular volume and a 17% reduction in posterior corpus callosum volume. No differences in whole brain, gray matter, or hippocampal volumes were observed.

CONCLUSION

Specific differences exist in the volumes of certain brain structures in adults who were born VLBW compared with their normal birth weight siblings.

Transcranial magnetic stimulation in children

Single and paired pulse transcranial magnetic stimulation (TMS) provide a non-invasive, painless method of probing the motor system. These techniques are of particular interest for studying maturation of the motor system and may provide insights into those developmental disabilities strongly associated with specific delays of motor development. This article will review studies using single pulse and paired pulse TMS in children, with particular reference to insights into neurodevelopment in children. It will also briefly touch on the potential of TMS as a diagnostic tool in neurological disorders. It will not address the use of repetitive TMS in children.

Performance on the IOWA card task by adolescents and adults

Performance on the Iowa Card Task (ICT) is impaired in several populations that demonstrate poor decision-making and risk-taking including patients with damage to the ventromedial prefrontal cortex. For some individuals, adolescence is a period of poor decision-making and risk-taking. Adolescence is also a period of neuroanatomic and neurochemical remodeling. There is evidence that neuropsychological functions of the prefrontal cortex change during adolescence; however, decision-making, as measured by the ICT, has not been systematically studied in adolescents over the age of 14 years. In the present study, 60 participants (30 female) in each of grades 6-12, and 60 young adults were administered the Iowa Card Task, the Wisconsin Card Sorting Task (WCST), a survey of impulsivity and excitement-seeking, and a quantity-frequency index of substance use. Results showed significant and steady improvement on the Iowa Card Task from the 6th grade to adulthood. Performance on the Iowa Card Task was not correlated with measures of impulsivity, excitement-seeking or reported individual substance use. There was one indication that poly-substance use was negatively correlated with performance on the ICT. Performance on the WCST was not significantly correlated with performance on the Iowa Card Task or any other measure. Across age, males and females had a different response pattern on the ICT. Females tended to choose cards associated with both immediate wins and with long-term outcome. Males tended to choose on the basis of long-term outcome. Results are discussed in terms of adolescent brain development and decision-making differences between males and females.

Magnetic resonance imaging study of corpus callosum abnormalities in patients with bipolar disorder

BACKGROUND

This study was conducted to further examine the hypothesis of abnormalities in size of corpus callosum in subjects with bipolar disorder.

METHODS

Sixteen right-handed DSM-IV bipolar I patients and 27 right-handed healthy control subjects were studied. A 1.5-T GE Signa magnet was used, and three-dimensional gradient echo imaging (spoiled gradient recall acquisition) was conducted. Area measurements of corpus callosum were obtained blindly, with a semi-automated software, by a well-trained rater.

RESULTS

Right-handed bipolar I patients had significantly smaller total corpus callosum, genu, posterior body, and isthmus areas compared with right-handed healthy control subjects (analysis of covariance with age, gender, and intracranial volume as covariates, p <.05). Partial correlation analyses, controlled for intracranial volumes, found a significant inverse relationship between age and total callosal, genu, anterior body, isthmus, and circularity in healthy control subjects (p <.05) but not in bipolar patients (p >.05).

CONCLUSIONS

Smaller callosal areas may lead to altered inter-hemispheric communication and be involved in the pathophysiology and cognitive impairment found in bipolar disorder.

Prenatal PCB exposure, the corpus callosum, and response inhibition

The present study reports the association between prenatal exposure to polychlorinated biphenyls (PCBs), the corpus callosum, and response inhibition in children who are 4.5 years old. Children (n = 189) enrolled in the Oswego study were tested using a continuous performance test. We measured (square millimeters) the splenium of the corpus callosum, a pathway implicated in the regulation of response inhibition, using magnetic resonance imaging. Results indicated a dose-dependent association between cord blood PCBs and errors of commission. Splenium size but not other brain areas predicted errors of commission (r(2) = 0.20), with smaller size associated with more errors of commission. There was an interaction between splenium size and PCB exposure. The smaller the splenium, the larger the association between PCBs and errors of commission. If the association between PCBs and response inhibition is indeed causal, then children with suboptimal development of the splenium are particularly vulnerable to these effects. These data await replication.

The shape of the fMRI BOLD response in children and adults changes systematically with age

We measured the shape of the BOLD response to visual stimulation in subjects between 7 and 61 years of age. We performed two experiments. In the first experiment, at low temporal resolution (TR = 1 s) and with long stimulus periods, we determined activated voxels in each subject. In the second experiment, at high temporal resolution (TR = 294 ms), we measured the response to an impulse stimulus in these voxels. We found that the shape of the time course changes systematically with age. Among the parameters whose age dependence we determined quantitatively, we found the smallest effect for the latency of the leading edge. Therefore, in order to avoid the potential confounds resulting from this effect, it may be appropriate to use the latency of the leading edge or the peak intensity of the BOLD signal, rather than its trailing edge or the area under the signal, as the salient variable in event-related studies that compare groups of different age.

Corpus callosum development in childhood-onset schizophrenia

OBJECTIVE

Corpus callosum (CC) size and interhemispheric communication differences have been reported between patients with schizophrenia and normal controls. Childhood-onset schizophrenia (COS) is a severe form of the disorder that is continuous with later-onset disorder. Corpus callosal area was examined for COS at initial scan and prospectively through adolescence, and related to other developmental abnormalities for this group.

METHOD

A total of 113 anatomic brain MRI scans were obtained from 55 COS (22 female) and 110 scans from 56 age- and gender-matched healthy volunteers (22 female), across ages 8-24. Baseline and prospective rescans were obtained at approximately 2-year intervals. The midsagittal areas for total corpus callosum and seven subregions were calculated using an automated system. Cross-sectional and longitudinal data were combined using mixed model regression analysis to compare developmental changes for the two groups.

RESULTS

No diagnostic differences were seen at time of initial scan. Longitudinally, and in contrast to healthy volunteers, patients with schizophrenia showed a significant difference in developmental trajectory for the area of the splenium, both before (p=0.012) and after (p=0.05) adjustment for total cerebral volume. The area of the splenium becomes significantly smaller in COS, starting at about age 22.

CONCLUSION

Patients with schizophrenia showed a significant difference in developmental trajectory for the splenial area, which seems to decline for COS. If replicated, this may reflect anticipated late occipital and extrastriate changes in brain regions.

Developmental aspects of language processing: fMRI of verbal fluency in children and adults

We examined developmental differences, in location and extent of fMRI language activation maps, between adults and children while performing a semantic fluency task. We studied 29 adults and 16 children with echo planar imaging BOLD fMRI at 1.5 T using covert semantic verbal fluency (generation of words to categories compared to rest) using a block design. Post task testing was administered to assess performance. Individual data were analyzed with an a priori region of interest approach from t maps (t = 4) and asymmetry indices (AI). Group studies were analyzed using SPM 99 (Wellcome, UK; fixed effect, corrected P < 0.0001). We found no significant differences in location or laterality of activation between adults and children for a semantic verbal fluency task. Adults activated more pixels than children in left inferior frontal gyrus and left middle frontal gyrus, but AIs were the similar across ages (r(2) < 0.09). Extent or laterality of activation was not affected by performance (r(2) < 0.15). The brain areas that process semantic verbal fluency are similar in children and adults. The laterality of activation does not change appreciably with age and appears to be strongly lateralized by age 7 years.

Corpus callosum: musician and gender effects

Previously we found that musicians have significantly larger anterior corpus callosum (CC). In the current study, we intended to replicate and extend our previous results using a new and larger sample of gender-matched subjects (56 right-handed professional musicians and 56 age- and handedness-matched controls). We found a significant gender x musicianship interaction for anterior and posterior CC size; male musicians had a larger anterior CC than non-musicians, while females did not show a significant effect of musicianship. The lack of a significant effect in females may be due to a tendency for a more symmetric brain organization and a disproportionately high representation of absolute pitch (AP) musicians among females. Although a direct causal effect between musicianship and alterations in the midsagittal CC size cannot be established, it is likely that the early commencement and continuous practice of bimanual motor training serves as an external trigger that can influence midsagittal CC size through changes in the actual callosal fiber composition and in the degree of myelinization, which will have implications for interhemispheric connectivity.

Deformation-based surface morphometry applied to gray matter deformation

We present a unified statistical approach to deformation-based morphometry applied to the cortical surface. The cerebral cortex has the topology of a 2D highly convoluted sheet. As the brain develops over time, the cortical surface area, thickness, curvature, and total gray matter volume change. It is highly likely that such age-related surface changes are not uniform. By measuring how such surface metrics change over time, the regions of the most rapid structural changes can be localized. We avoided using surface flattening, which distorts the inherent geometry of the cortex in our analysis and it is only used in visualization. To increase the signal to noise ratio, diffusion smoothing, which generalizes Gaussian kernel smoothing to an arbitrary curved cortical surface, has been developed and applied to surface data. Afterward, statistical inference on the cortical surface will be performed via random fields theory. As an illustration, we demonstrate how this new surface-based morphometry can be applied in localizing the cortical regions of the gray matter tissue growth and loss in the brain images longitudinally collected in the group of children and adolescents.

Sex differences in brain maturation in maltreatment-related pediatric posttraumatic stress disorder

BACKGROUND

Recent investigations suggested that pediatric posttraumatic stress disorder (PTSD) is associated with adverse brain development. However, sex differences are poorly understood.

METHODS

In this study, 61 medically healthy children and adolescents (31 males and 30 females) with chronic PTSD secondary to abuse, who had similar trauma and mental health histories, and 122 healthy controls (62 males and 60 females) underwent comprehensive psychiatric assessments and an anatomical MRI brain scan.

RESULTS

When gender groups were analyzed separately, findings of larger prefrontal lobe CSF volumes and smaller midsagittal area of the corpus callosum subregion 7 (splenium) were seen in both boys and girls with maltreatment-related PTSD compared to their gender-matched comparison subjects. Subjects with PTSD did not show the normal age related increases in the area of the total corpus callosum and its region 7 (splenium) compared to non-maltreated subjects; however, this finding was more prominent in males with PTSD. Significant sex by group effects demonstrated smaller cerebral volumes and corpus callosum regions 1 (rostrum) and 6 (isthmus) in PTSD males and greater lateral ventricular volume increases in maltreated males with PTSD than maltreated females with PTSD.

CONCLUSIONS

These data suggest that there are sex differences in the brain maturation of boys and girls with maltreatment-related PTSD. Longitudinal MRI brain investigations of childhood PTSD and the relationship of gender to psychosocial outcomes are warranted.

The neurobiological consequences of early stress and childhood maltreatment

Early severe stress and maltreatment produces a cascade of neurobiological events that have the potential to cause enduring changes in brain development. These changes occur on multiple levels, from neurohumoral (especially the hypothalamic-pituitary-adrenal [HPA] axis) to structural and functional. The major structural consequences of early stress include reduced size of the mid-portions of the corpus callosum and attenuated development of the left neocortex, hippocampus, and amygdala. Major functional consequences include increased electrical irritability in limbic structures and reduced functional activity of the cerebellar vermis. There are also gender differences in vulnerability and functional consequences. The neurobiological sequelae of early stress and maltreatment may play a significant role in the emergence of psychiatric disorders during development.

A callosal transfer deficit in children with developmental language disorder

Twenty-two control children (aged 6-12 years) and forty-three children with developmental language disorder (DLD) (aged 7-12 years) received a test of callosal transfer of tactile information. Among the children with dysphasia, 30 had a diagnosis of receptive dysphasia and 13 of expressive dysphasia. Both control children and children with DLD made a significantly larger number of errors in the crossed localization condition (implying callosal transfer of tactile information) versus the uncrossed localization condition. In the crossed localization condition, children with DLD made a significantly larger number of errors than controls, while no differences were found in the two groups of children with DLD. These data suggest that the corpus callosum may be involved in the pathogenesis of DLD.

Millisecond by millisecond, year by year: normative EEG microstates and developmental stages

Most studies of continuous EEG data have used frequency transformation, which allows the quantification of brain states that vary over seconds. For the analysis of shorter, transient EEG events, it is possible to identify and quantify brain electric microstates as subsecond time epochs with stable field topography. These microstates may correspond to basic building blocks of human information processing. Microstate analysis yields a compact and comprehensive repertoire of short lasting classes of brain topographic maps, which may be considered to reflect global functional states. Each microstate class is described by topography, mean duration, frequency of occurrence and percentage analysis time occupied. This paper presents normative microstate data for resting EEG obtained from a database of 496 subjects between the age of 6 and 80 years. The extracted microstate variables showed a lawful, complex evolution with age. The pattern of changes with age is compatible with the existence of developmental stages as claimed by developmental psychologists. The results are discussed in the framework of state dependent information processing and suggest the existence of biologically predetermined top-down processes that bias brain electric activity to functional states appropriate for age-specific learning and behavior.

Neuropsychology and temporal lobe epilepsy

The purpose of this article is to review aspects of the neuropsychology of temporal lobe epilepsy. Evidence will be presented to demonstrate that the cognitive consequences of this focal seizure disorder can be more generalized in nature than expected. Consistent with the extratemporal neurocognitive findings, careful quantitative magnetic resonance imaging volumetrics have shown that structural brain changes may be detected outside the temporal lobes. Many factors can potentially affect cognition and brain structure. We focus on the potential neurodevelopmental impact of early-onset temporal lobe epilepsy on brain structure and cognition positing that this disorder can have both immediate and lifespan implications for cognition and psychosocial status.

Development of the corpus callosum in childhood, adolescence and early adulthood

The corpus callosum (CC) is the major commissure connecting the cerebral hemispheres and there is evidence of its continuing development into young adulthood [Ann. Neurol. 34 (1993) 71]. Yet, little is known about changes in the size and tissue characteristics of its sub-regions. The sub-regions of the CC (genu, body, isthmus and splenium) are topographically organized to carry interhemispheric fibres representing heteromodal and unimodal cortical brain regions. Studies of the development of each of these sub-regions can therefore provide insights into the time course of brain development. We assessed age-related changes in the size and the signal intensities (SI) of the subregions of the corpus callosum in the Magnetic Resonance Imaging (MRI) scans of a cross-sectional sample of 109 healthy young individuals aged 7-32 years. Age was significantly positively correlated with the size of the callosal sub-regions (with the exception of the isthmus). On the other hand, there was an age-related decrease in SI across all the CC sub-regions. The rates of CC regional size increases appeared to be most pronounced in childhood. By contrast, SI decreases occurred during childhood and adolescence but reached an asymptote during young adulthood. Finally, the observed size and SI changes were similar across CC sub-regions. The observed increases in CC size in conjunction with the decreases in signal intensity reflect continued maturation of the structure from childhood through young adulthood. An increase in axonal size may underlie growth in the size of the CC during childhood. The continued decrease in the CC signal intensity during adolescence may in addition be related to ongoing maturation of the axonal cytoskeleton. CC maturational changes appeared synchronous across sub-regions suggesting parallel maturation of diverse brain regions during childhood and adolescence.

Anatomical MRI of the developing human brain: what have we learned?

OBJECTIVE

To critically review and integrate the existing literature on magnetic resonance imaging (MRI) studies of the normally developing brain in childhood and adolescence and discuss the implications for clinical MRI studies.

METHOD

Changes in regional brain volume with age and differences between the sexes are summarized from reports in refereed journal articles pertaining to MRI of the developing human brain.

RESULTS

White matter volume increases with age. Gray matter volumes increase during childhood and then decrease before adulthood. On average, boys have larger brains than girls; after correction for overall brain volume the caudate is relatively larger in girls, and the amygdala is relatively larger in boys. Differences are of clinical interest given gender-related differences in the age of onset, symptomatology, and prevalence noted for nearly all childhood-onset psychiatric disorders. Attention-deficit/hyperactivity disorder is frequently used as an example to demonstrate these points.

CONCLUSIONS

Understanding the developmental trajectories of normal brain development and differences between the sexes is important for the interpretation of clinical imaging studies.

A unified statistical approach to deformation-based morphometry

We present a unified statistical framework for analyzing temporally varying brain morphology using the 3D displacement vector field from a nonlinear deformation required to register a subject's brain to an atlas brain. The unification comes from a single model for structural change, rather than two separate models, one for displacement and one for volume changes. The displacement velocity field rather than the displacement itself is used to set up a linear model to account for temporal variations. By introducing the rate of the Jacobian change of the deformation, the local volume change at each voxel can be computed and used to measure possible brain tissue growth or loss. We have applied this method to detecting regions of a morphological change in a group of children and adolescents. Using structural magnetic resonance images for 28 children and adolescents taken at different time intervals, we demonstrate how this method works.

Developmental aspects of pediatric fMRI: considerations for image acquisition, analysis, and interpretation

Functional MRI provides a powerful means to identify and trace the evolution, development, and consolidation of cognitive neural networks through normal childhood. Neural network perturbations due to disease and other adverse factors during development can also be explored. Studies performed to date suggest that normal children older than 5 years show activation maps comparable to adults for similar cognitive paradigms. Minor differences in adult and pediatric activation maps may reflect age dependent strategies or maturation of cognitive networks. However, there are important physiologic and anatomic differences in children, varying with age, that may affect the acquisition, analysis, and interpretation of pediatric fMRI data. Differences between children and adult fMRI comparison studies may reflect technical aspects of data acquisition as much as developmental and brain maturation factors.

Callosal transfer in different subtypes of developmental dyslexia

Sixteen controls (age 6-13) and 20 native Italian children with developmental dyslexia (age 7-15) received a test of callosal transfer of tactile information. Among the dyslexic children, 7 had a diagnosis of L-type, 7 of P-type and 6 of M-type dyslexia according to Bakker's classification. Both control children and children with dyslexia made a significantly larger number of errors in the crossed localization condition (implying callosal transfer of tactile information) vs. the uncrossed condition. In the same condition, children with dyslexia made a significantly larger number of errors than controls. In the crossed localization condition L-types and M-types made a significantly larger number of errors than P-types and controls, while there was no significant difference in performance between P-types and controls. These findings are discussed in terms of defective callosal transfer or deficient somatosensory representation in children with L- and M-dyslexia.