Normal brain development and aging: quantitative analysis at in vivo MR imaging in healthy volunteers

Diffusion tensor imaging of neurodevelopment in children and young adults

Diffusion tensor magnetic resonance imaging (DTI) was used to study regional changes in the brain's development from childhood (8-12 years, mean 11.1 +/- 1.3, N = 32) to young adulthood (21-27 years, mean 24.4 +/- 1.8, N = 28). Mean diffusivity (Trace/3 apparent diffusion coefficient, ADC) and fractional anisotropy (FA) were measured in 30 regions of interest (ROIs) in 13 distinct brain structures. Correlational analysis was performed to detect changes within 8-12 years and within 21-27 years, and group analysis to compare childhood diffusion properties with young adult values. Increases of fractional anisotropy were seen in the genu of the corpus callosum, splenium of the corpus callosum, corona radiata, putamen, and head of the caudate nucleus within 8-12 years, and also between childhood and young adulthood. Reductions in Trace/3 ADC were observed in 9 of 13 structures within 8-12 years and into young adulthood as well. DTI demonstrates more widespread changes in the brain's microstructure with maturation than previous reports using conventional T1-weighted MRI scans. These findings suggest a continuation of the brain's microstructural development through adolescence.

Longitudinal mapping of cortical thickness and brain growth in normal children

Recent advances in magnetic resonance imaging (MRI) technology now allow the tracing of developmental changes in the brains of children. We applied computer-matching algorithms and new techniques for measuring cortical thickness (in millimeters) to the structural MRI images of 45 children scanned twice (2 yr apart) between the ages 5 and 11. Changes in brain size were also assessed, showing local brain growth progressing at a rate of approximately 0.4-1.5 mm per year, most prominently in frontal and occipital regions. Estimated cortical thickness ranged from 1.5 mm in occipital regions to 5.5 mm in dorsomedial frontal cortex. Gray matter thinning coupled with cortical expansion was highly significant in right frontal and bilateral parieto-occipital regions. Significant thickening was restricted to left inferior frontal (Broca's area) and bilateral posterior perisylvian (Wernicke's area on the left) regions. In the left hemisphere, gray matter thickness was correlated with changing cognitive abilities. For the first time, developmental changes in gray matter thickness, brain size, and structure-function relationships have been traced within the same individuals studied longitudinally during a time of rapid cognitive development.

When is the brain enlarged in autism? A meta-analysis of all brain size reports

BACKGROUND

Multiple studies have reported increased brain size in autism, while others have found no difference from normal. These conflicting results may be due to a lack of accounting for age-related changes in brain enlargement, use of small sample sizes, or differences in data acquisition methods.

METHODS

Reports of autism head circumference (HC), magnetic resonance imaging (MRI), and post-mortem brain weight (BW) that met specific criteria were identified and analyzed. Percent difference from normal values (%Diff) and standardized mean differences (SMD) were calculated to compare brain size across studies and measurement methods. Curve fitting, analysis of variance, and heterogeneity analyses were applied to assay the effects of age and measurement type on reported brain size in autism.

RESULTS

A fitted curve of HC and MRI %Diff values from 15 studies revealed a largely consistent pattern of brain size changes. Specifically, brain size in autism was slightly reduced at birth, dramatically increased within the first year of life, but then plateaued so that by adulthood the majority of cases were within normal range. Analysis of variance of MRI and post-mortem %Diff values by age group (young child, older child, adult) and measurement type (MRI, BW) revealed a significant main effect of both age and measurement type, with the youngest ages (2-5) showing the greatest deviation from normal. Random effects heterogeneity analysis revealed a significant effect of age on HC and MRI SMD.

CONCLUSIONS

These findings reveal a period of pathological brain growth and arrest in autism that is largely restricted to the first years of life, before the typical age of clinical identification. Study of the older autistic brain, thus, reflects the outcome, rather than the process, of pathology. Future research focusing on this early process of brain pathology will likely be critical to elucidate the etiology of autism.

A quantitative computed tomography assessment of brain weight, volume, and specific gravity in severe head trauma

BACKGROUND

Computed tomography DICOM images analysis allows a quantitative measurement of organ weight, volume and specific gravity in humans.

METHODS

The brain weight, volume and specific gravity of 15 traumatic brain-injury patients (3+/-2 days after trauma) were computed using a specially designed software (BrainView). Data were compared with those obtained from 15 healthy subjects paired for age and overall intracranial volume.

RESULTS

Hemisphere weight were 91 g higher in patients than in controls (1167+/-101 vs 1076+/-112 g; p<0.05). Specific gravity of hemispheres (1.0367+/-0.0017 vs 1.0335+/-0.0012 g/ml; p<0.001), brainstem (1.0302+/-0.0016 vs 1.0277+/-0.0015 g/ml; p<0.001) and cerebellum (1.0396+/-0.0020 vs 1.0375+/-0.0015 g/ml; p<0.05) was significantly higher in traumatic brain injury (TBI) patients than in controls (all p<0.0001 without interaction). This increase in specific gravity was evenly distributed between the hemispheres, the brainstem and the cerebellum, and the grey and white matter. It was more pronounced in the rostral than in the caudal areas of the hemispheres. It was independent of the volume of brain contusion, of the mechanism of head injury, of natremia and of initial Glasgow coma score.

CONCLUSION

Human TBI patients present a diffuse increase in specific gravity. This observation is in sharp opposition with the data derived from the experimental literature.

[Correlation between cranial vault size and brain size over time: preliminary MRI evaluation]

OBJECTIVES

To correlate changes of cranial vault measurements of an adult population during the aging process with brain size using the maximum width of the third ventricle in the axial AC-PC plane.

MATERIALS AND METHODS

Prospective study of 126 adult subjects (range: 20 to 80 years) with normal brain MRI and without history of neuropsychiatric disorder. MEASUREMENTS INCLUDED: Cranial vault (Maximum length: Glabella-Opisthocranion, Maximum width: euryon-euryon, and maximum height: Basion-Vertex) measurements and maximum width of the third ventricle in the A C-PC plane.

RESULTS

Vault measurements (length, width, high) were similar for every age group, irrespective of gender. The variability of cranial vault measurements between individuals was low (<1 cm). Cranial vault measurements were larger for men, but this was not significant when adjusted for body height Comparatively, a gradual widening of the third ventricle, with an exponential behavior, was observed with advancing age.

CONCLUSION

Our results indicate that cranial vault measurements are stable over time (between 20-80 years) comparatively to brain atrophy with advancing age. The low variability of cranial vault measurements and their stability over time should be taken into account during segmentation and normalization of brain parenchymal structures.

Individual and Population Penalized Regression Splines for Accelerated Longitudinal Designs

In an accelerated longitudinal design (ALD), individuals enter the study at different points of their growth trajectory and are observed over a short time span relative to the entire time span of interest. ALD data are combined across independent units to provide an estimate of an overall population curve and predictions of individual patterns of change. As a modest extension of the work of Ruppert et al. (2003, Semiparametric Regression, Cambridge University Press), we develop a computationally efficient procedure for the application of longitudinal semiparametric methods under ALD sampling schemes. We compare balanced and complete longitudinal designs to ALDs using the Berkeley Growth Study data and apply our method to longitudinal magnetic resonance imaging (MRI) brain structure size (volume) measurements from an ongoing developmental study. Potential applications extend beyond growth studies to many other fields in which cost and feasibility constraints impose restrictions on sample size and on the numbers and timings of repeated measurements across subjects.

Sexual dimorphism in mammalian gene expression

Males and females have obvious phenotypic differences; they also exhibit differences related to health, life span, cognitive abilities and have different responses to diseases such as anemia, coronary heart disease, hypertension and renal dysfunction. Although the anatomical, hormonal and chemical differences between the sexes are well known, there are few molecular descriptors for gender-specific physiological traits and health risks. Recent studies using microarrays and other methods have made significant progress towards elucidating the molecular differences between mammalian sexes in a variety of tissues and towards identifying the transcription factors that regulate sex-biased gene expression. These findings are providing new insights into the molecular and genetic differences that dictate the different behaviors and physiologies of mammalian sexes.

Aging, stress and the hippocampus

Functional loss often occurs in many body systems (e.g., endocrine, cognitive, motor) with the passage of years, but there is great individual variation in the degree of compromise shown. The current focus on brain aging will continue because demographic trends indicate that the average lifespan will show a continued increase. There is increasing emphasis on understanding how aging contributes to a decline in brain functions, cognition being a prime example. This is due in part to the fact that dementias and other losses in brain function that sometimes accompany aging cause an obvious decline in the quality of life and these deficits are of more concern as the number of elderly increase. Stress also is a ubiquitous aspect of life and there is now a greater interest in understanding the role of stress and the stress response in brain aging. The key role of the hippocampus and its related brain structures in cognition, as well as in the feedback control of the response to stress, have made this brain area a logical focus of investigation for those interested in the impact of stress on brain aging. Here, we describe how the hippocampus changes with age and we examine the idea that age-related changes in the secretion patterns of the hypothalamic-pituitary adrenal (HPA) axis can contribute to aging of this structure. We also examine the proposal that stress, perhaps due to compromised HPA axis function, can contribute to hippocampal aging through exposure to excessive levels of glucocorticoids. The aging hippocampus does not appear to suffer a generalized loss of cells or synapses, although atrophy of the structure may occur in humans. Thus, age-related cognitive impairments are likely related to other neurobiological alterations that could include changes in the signaling, information encoding, plasticity, electrophysiological or neurochemical properties of neurons or glia. Although excessive levels of glucocorticoids are able to interfere with cognition, as well as hippocampal neuronal integrity, and aging is sometimes accompanied by an increase in these steroids because of inadequate feedback control of the HPA axis, none of these are a foregone consequence of aging. The general preservation of cells and the plastic potential of the hippocampus provide a focus for the development of pharmacological, nutritive or lifestyle strategies to combat age-related declines in the hippocampus as well as other brain areas.

Age- and sex-related effects on the neuroanatomy of healthy elderly

Effects of age and sex, and their interaction on the structural brain anatomy of healthy elderly were assessed thanks to a cross-sectional study of a cohort of 662 subjects aged from 63 to 75 years. T1- and T2-weighted MRI scans were acquired in each subject and further processed using a voxel-based approach that was optimized for the identification of the cerebrospinal fluid (CSF) compartment. Analysis of covariance revealed a classical neuroanatomy sexual dimorphism, men exhibiting larger gray matter (GM), white matter (WM), and CSF compartment volumes, together with larger WM and CSF fractions, whereas women showed larger GM fraction. GM and WM were found to significantly decrease with age, while CSF volume significantly increased. Tissue probability map analysis showed that the highest rates of GM atrophy in this age range were localized in primary cortices, the angular and superior parietal gyri, the orbital part of the prefrontal cortex, and in the hippocampal region. There was no significant interaction between "Sex" and "Age" for any of the tissue volumes, as well as for any of the tissue probability maps. These findings indicate that brain atrophy during the seventh and eighth decades of life is ubiquitous and proceeds at a rate that is not modulated by "Sex".

T2rho-weighted contrast in MR images of the human brain

In this work, the feasibility of using T2rho weighting as an MR contrast mechanism is evaluated. Axial images of a human brain were acquired using a single-slice spin-lock T2rho-weighted pulse sequence and compared to analogous T2-weighted images of the same slice. The contrast between white matter and gray matter in T2rho-weighted images was approximately 40% greater than that from T2-weighted data. These preliminary data suggest that the novel contrast mechanism of T2rho can be used to yield high-contrast T2-like images.

Regulation of cytochrome oxidase activity in the rat forebrain throughout adulthood

Measures of metabolic activity can provide useful indices of the effects of aging on neural function, since sustained changes in neural activity alter metabolic demand and the activity of metabolic enzymes. Previous reports of effects of aging on key enzymes for oxidative metabolism are mixed, however, with some reports that activity declines in the aging brain and others that activity remains stable or increases. We used high-resolution, quantitative histochemistry to test whether cytochrome oxidase (CO) activity changes in the forebrain during adulthood and senescence, measuring activity in each layer of the hippocampus and several cerebral cortical areas. In most forebrain regions, average cytochrome oxidase activity was slightly higher in middle-aged than in young adult rats but did not differ between middle-aged and old rats. Thus, there was no significant change in cytochrome oxidase activity with senescence. Additional analyses indicated that cytochrome oxidase activity is regulated regionally in the brain, as well as focally, and that differences in regional regulation may contribute to variation in CO activity among individuals, which was greater in young and old rats than in middle-aged animals.

Brain overgrowth in autism during a critical time in development: implications for frontal pyramidal neuron and interneuron development and connectivity

While abnormalities in head circumference in autism have been observed for decades, it is only recently that scientists have begun to focus in on the developmental origins of such a phenomenon. In this article we review past and present literature on abnormalities in head circumference, as well as recent developmental MRI studies of brain growth in this disorder. We hypothesize that brain growth abnormalities are greatest in frontal lobes, particularly affecting large neurons such as pyramidal cells, and speculate how this abnormality might affect neurofunctional circuitry in autism. The relationship to clinical characteristics and other disorders of macrencephaly are discussed.

Regional Brain Changes in Aging Healthy Adults: General Trends, Individual Differences and Modifiers

Brain aging research relies mostly on cross-sectional studies, which infer true changes from age differences. We present longitudinal measures of five-year change in the regional brain volumes in healthy adults. Average and individual differences in volume changes and the effects of age, sex and hypertension were assessed with latent difference score modeling. The caudate, the cerebellum, the hippocampus and the association cortices shrunk substantially. There was minimal change in the entorhinal and none in the primary visual cortex. Longitudinal measures of shrinkage exceeded cross-sectional estimates. All regions except the inferior parietal lobule showed individual differences in change. Shrinkage of the cerebellum decreased from young to middle adulthood, and increased from middle adulthood to old age. Shrinkage of the hippocampus, the entorhinal cortices, the inferior temporal cortex and the prefrontal white matter increased with age. Moreover, shrinkage in the hippocampus and the cerebellum accelerated with age. In the hippocampus, both linear and quadratic trends in incremental age-related shrinkage were limited to the hypertensive participants. Individual differences in shrinkage correlated across some regions, suggesting common causes. No sex differences in age trends except for the caudate were observed. We found no evidence of neuroprotective effects of larger brain size or educational attainment.

Brain development in autism: early overgrowth followed by premature arrest of growth

Due to the relatively late age of clinical diagnosis of autism, the early brain pathology of children with autism has remained largely unstudied. The increased use of retrospective measures such as head circumference, along with a surge of MRI studies of toddlers with autism, have opened a whole new area of research and discovery. Recent studies have now shown that abnormal brain overgrowth occurs during the first 2 years of life in children with autism. By 2-4 years of age, the most deviant overgrowth is in cerebral, cerebellar, and limbic structures that underlie higher-order cognitive, social, emotional, and language functions. Excessive growth is followed by abnormally slow or arrested growth. Deviant brain growth in autism occurs at the very time when the formation of cerebral circuitry is at its most exuberant and vulnerable stage, and it may signal disruption of this process of circuit formation. The resulting aberrant connectivity and dysfunction may lead to the development of autistic behaviors. To discover the causes, neural substrates, early-warning signs and effective treatments of autism, future research should focus on elucidating the neurobiological defects that underlie brain growth abnormalities in autism that appear during these critical first years of life.

fMRI evidence of compensatory mechanisms in older adults at genetic risk for Alzheimer disease

OBJECTIVE

To determine whether APOE genotype influences brain response and whether nonverbal stimuli generate findings comparable with those of previous studies that used verbal stimuli. The relationship between APOE genotype and blood oxygenation level dependent (BOLD) brain response was examined during a picture-encoding task in nondemented older adults.

METHODS

Twenty nondemented participants with normal episodic memory function were divided into two groups based on the presence (n = 10) or absence (n = 10) of the APOE epsilon4 allele. Picture learning was completed during functional MRI in a blocked design alternating between experimental (novel pictures) and control (repeated picture) conditions.

RESULTS

Nondemented older adults with an APOE epsilon4 allele showed greater magnitude and extent of BOLD brain response during learning of new pictures relative to their matched epsilon3 counterparts. Different patterns and directions of association between hippocampal activity and learning and memory performance were also demonstrated.

CONCLUSIONS

The results suggest that brain response differences are not due to poorer general memory abilities, differential atrophy, or brain response during control conditions, but instead appear to be directly influenced by APOE genotype. Results are consistent with a compensatory hypothesis wherein older adults at genetic risk for Alzheimer disease by virtue of the APOE epsilon4 allele appear to require additional cognitive effort to achieve comparable performance levels on tests of episodic memory encoding.

Localized enlargement of the frontal cortex in early autism

BACKGROUND

Evidence from behavioral, imaging, and postmortem studies indicates that the frontal lobe, as well as other brain regions such as the cerebellum and limbic system, develops abnormally in children with autism. It is not yet clear to what extent the frontal lobe is affected; that is, whether all regions of frontal cortex show the same signs of structural maldevelopment.

METHODS

In the present study, we measured cortical volume in four subregions of the frontal cortex in 2-year-old to 9-year-old boys with autism and normal control boys.

RESULTS

The dorsolateral region showed a reduced age effect in patients when compared with control subjects, with a predicted 10% increase in volume from 2 years of age to 9 years of age compared with a predicted 48% increase for control subjects. In a separate analysis, dorsolateral and medial frontal regions were significantly enlarged in patients aged 2 to 5 years compared with control subjects of the same age, but the precentral gyrus and orbital cortex were not.

CONCLUSIONS

These data indicate regional variation in the degree of frontocortical overgrowth with a possible bias toward later developing or association areas. Possible mechanisms for these regional differences are discussed.

Auditory spatial localization and attention deficits in autistic adults

The objective of this study was to compare autistic adults and matched control subjects in their ability to focus attention selectively on a sound source in a noisy environment. Event-related brain potentials (ERPs) were recorded while subjects attended to a fast paced sequence of brief noise bursts presented in free-field at a central or peripheral location. Competing sequences of noise bursts at adjacent locations were to be ignored. Both behavioral measures of target detection and auditory ERP amplitudes indicated that control subjects were able to focus their attention more sharply on the relevant sound source than autistic subjects. These findings point to a fundamental deficit in the spatial focusing of auditory attention in autism, which may be a factor that impedes social interactions and sensory-guided behavior, particularly in noisy environments.

Cortical volume and speed-of-processing are complementary in prediction of performance intelligence

The rationale for the present study was to investigate the relationship between cortical volume, the latency of the ERP component P3a (as a measure of speed-of-processing), and performance intelligence (not adjusted for age differences). Seventy-one participants aged 20-88 years underwent a visual 3-stimuli oddball ERP task, an MRI-scan, and intelligence testing. P3a latency and cortical volume shared 9% variance (p<.05) and both were significantly related to performance intelligence (R2=.26 and .40, respectively). The amount of explained variance increased significantly (to R2=.51) when both measures were used as simultaneous predictors. When a path diagram was constructed including age as an exogenous variable, P3a latency and cortical volume both significantly predicted performance intelligence, but were no longer related to one another. The main conclusion from the study is that speed and size are complementary in prediction of performance intelligence, and the theoretical implications are discussed.

Age does not increase rate of forgetting over weeks--neuroanatomical volumes and visual memory across the adult life-span

The aim of the study was to investigate whether age affects visual memory retention across extended time intervals. In addition, we wanted to study how memory capabilities across different time intervals are related to the volume of different neuroanatomical structures (right hippocampus, right cortex, right white matter). One test of recognition (CVMT) and one test of recall (Rey-Osterrieth Complex Figure Test) were administered, giving measures of immediate recognition/recall, 20-30 min recognition/recall, and recognition/recall at a mean of 75 days. Volumetric measures of right hemisphere hippocampus, cortex, and white matter were obtained through an automated labelling procedure of MRI recordings. Results did not demonstrate a steeper rate of forgetting for older participants when the retention intervals were increased, indicating that older people have spared ability to retain information in the long-term store. Differences in neuroanatomical volumes could explain up to 36% of the variance in memory performance, but were not significantly related to rates of forgetting. Cortical volume and hippocampal volume were in some cases independent as predictors of memory function. Generally, cortical volume was a better predictor of recognition memory than hippocampal volume, while the 2 structures did not differ in their predictive power of recall abilities. While neuroanatomical volumetric differences can explain some of the differences in memory functioning between younger and older persons, the hippocampus does not seem to be unique in this respect.

Pharmacokinetics Following Intraventricular Administration of Chemotherapy in Patients with Neoplastic Meningitis

Intraventricular administration of chemotherapy is one approach to overcoming the limited distribution of anticancer drugs and their active metabolites into the CNS. This form of regional chemotherapy has led to effective treatment of occult and overt meningeal leukaemia in humans. In contrast, the efficacy of this therapy is extremely limited in the treatment of leptomeningeal dissemination of various solid tumours. Pharmacokinetic studies of the commonly intraventricularly applied anticancer agents in humans have demonstrated that, using low drug doses, very high drug concentrations can be achieved in the cerebrospinal fluid (CSF) and relatively high concentrations in the leptomeninges but not in the brain tissue and the plasma. Therefore, this approach is not an effective treatment for bulky disease of brain tissue, and results in minimal systemic toxicity. In comparison with intralumbar administration, lower interpatient variability of CSF drug concentrations and improved clinical efficacy were observed. 'Concentration x time' schedules, i.e. frequent small drug doses over a short period, enable long-term CSF exposure to cytotoxic drug concentrations while avoiding excessively high and potentially neurotoxic drug concentrations. The technique of ventriculolumbar cerebrospinal perfusion delivers continuously high drug concentrations throughout the CSF for several hours, but its widespread use is limited by the technical complexities of this approach. In this article, the dosages, schedules and pharmacokinetic data of routinely used intraventricular agents in humans, e.g. methotrexate, cytarabine, glucocorticoids and thiotepa, are outlined in detail. In addition, pharmacokinetic data of investigational agents for intraventricular administration (diaziquone, DTC 101, mercaptopurine, mafosfamide, etoposide, topotecan, nimustine [ACNU] and bleomycin) are presented. Better understanding of the CSF pharmacology of these drugs is an essential prerequisite for safe, effective administration of these drugs. Investigational efforts are underway to verify the feasibility and efficacy of different dosages, schedules and combination therapies of these new intra-CSF agents. Current and future clinical research should also focus on methods allowing the delivery of tumoricidal drug concentrations for extended periods into the CSF and the brain tissue while minimising neurotoxicity and systemic toxicity (e.g. liposomal drug preparations, monoclonal antibodies, immunotoxins and gene therapy).

Quantitative MRI: hidden age-related changes in brain tissue

The advent of MRI has made a remarkable progress in the understanding of age-related brain changes providing a noninvasive tool to study in vivo the normally aging individuals at multiple time points. However, conventional MRI techniques are unable to detect and quantify age-related microstructural changes that have been documented at the post-mortem examination of brain tissues. More sophisticated, quantitative MR techniques such as magnetization transfer imaging, diffusion tensor imaging, and proton MR spectroscopy have been shown to be sensitive to microstructural and metabolic changes that occur in gray and white matter over the course of life span. This review highlights some of these innovative, quantitative MR techniques that are particularly relevant for the study of occult age-related brain tissue changes. Characterization of the in vivo patterns of molecular and cellular changes that occur in the normal aging brain is of crucial importance to understand the pathophysiology of normal cognitive decline and to interpret observed changes in neurodegenerative diseases.

Sensitivity and reproducibility of a new fast 3D segmentation technique for clinical MR-based brain volumetry in multiple sclerosis

Fast, reliable and easy-to-use methods to quantify brain atrophy are of increasing importance in clinical studies on neuro-degenerative diseases. Here, ILAB 4, a new volumetry software that uses a fast semi-automated 3D segmentation of thin-slice T1-weighted 3D MR images based on a modified watershed transform and an automatic histogram analysis was evaluated. It provides the cerebral volumes: whole brain, white matter, gray matter and intracranial cavity. Inter- and intra-rater reliability and scan-rescan reproducibility were excellent in measuring whole brain volumes (coefficients of variation below 0.5%) of volunteers and patients. However, gray and white matter volumes were more susceptible to image quality. High accuracy of the absolute volume results (+/-5 ml) were shown by phantom and preparation measurements. Analysis times were 6 min for processing of 128 slices. The proposed technique is reliable and highly suitable for quantitative studies of brain atrophy, e.g., in multiple sclerosis.

Mapping changes in the human cortex throughout the span of life

In this review, the authors summarize the literature on brain morphological changes that occur throughout the human life span from childhood into old age. They examine changes observed postmortem and in vivo where various brain MRI analytic methods have been applied. They evaluate brain changes observed with volumetric image analytic methods and voxel-based morphometric methods that may be used to better localize where changes occur. The primary focus of the review is on recent studies using state-of-the-art cortical pattern-matching techniques to assess age-related changes in cortical asymmetries, gray matter distribution, and brain growth across various age spans. The authors attempt to integrate findings from the in vivo studies with results from postmortem studies and analyze the complicated question of when brain maturation stops and brain aging begins. Analyzing the regional patterns of change initiated at various ages may help elucidate relationships between changing brain morphology and changing cognitive functions that occur throughout life. Long-range longitudinal studies, correlations between imaging and postmortem data, and more advanced image acquisition and analysis technologies will be needed to fully interpret brain morphological changes observed in vivo in relation to development and aging.

A unified approach for morphometric and functional data analysis in young, old, and demented adults using automated atlas-based head size normalization: reliability and validation against manual measurement of total intracranial volume

Atlas normalization, as commonly used by functional data analysis, provides an automated solution to the widely encountered problem of correcting for head size variation in regional and whole-brain morphometric analyses, so long as an age- and population-appropriate target atlas is used. In the present article, we develop and validate an atlas normalization procedure for head size correction using manual total intracranial volume (TIV) measurement as a reference. The target image used for atlas transformation consisted of a merged young and old-adult template specifically created for cross age-span normalization. Automated atlas transformation generated the Atlas Scaling Factor (ASF) defined as the volume-scaling factor required to match each individual to the atlas target. Because atlas normalization equates head size, the ASF should be proportional to TIV. A validation analysis was performed on 147 subjects to evaluate ASF as a proxy for manual TIV measurement. In addition, 19 subjects were imaged on multiple days to assess test-retest reliability. Results indicated that the ASF was (1) equivalent to manual TIV normalization (r = 0.93), (2) reliable across multiple imaging sessions (r = 1.00; mean absolute percentage of difference = 0.51%), (3) able to connect between-gender head size differences, and (4) minimally biased in demented older adults with marked atrophy. Hippocampal volume differences between nondemented (n = 49) and demented (n = 50) older adults (measured manually) were equivalent whether corrected using manual TIV or automated ASF (effect sizes of 1.29 and 1.46, respectively). To provide normative values, ASF was used to automatically derive estimated TIV (eTIV) in 335 subjects aged 15-96 including both clinically characterized nondemented (n = 77) and demented (n = 90) older adults. Differences in eTIV between nondemented and demented groups were negligible, thus failing to support the hypothesis that large premorbid brain size moderates Alzheimer's disease. Gender was the only robust factor that influenced eTIV. Men showed an approximately approximately 12% larger eTIV than women. These results demonstrate that atlas normalization using appropriate template images provides a robust, automated method for head size correction that is equivalent to manual TIV correction in studies of aging and dementia. Thus, atlas normalization provides a common framework for both morphometric and functional data analysis.

Memory and executive function in older adults: relationships with temporal and prefrontal gray matter volumes and white matter hyperintensities

Forty-eight healthy adults aged 65-85 were recruited for structural magnetic resonance scans after an extensive neuropsychological battery that ensured a high degree of variability across the sample in performance on long-term memory tests, and on tests traditionally thought to rely on prefrontal cortex. Gray matter volumes were measured for three gyri in the frontal lobe (superior, middle, inferior), six gyri in the temporal lobe (superior, middle, inferior, fusiform, parahippocampal, and hippocampus), and the occipital lobe. Gray matter volumes declined across the age range evaluated, but with substantial regional variation--greatest in the inferior frontal, superior temporal, and middle temporal gyri but negligible in the occipital lobe. Both memory performance and executive function declined as the number of hyperintense regions in the subcortical white matter increased. Memory performance was also significantly correlated with gray matter volumes of the middle frontal gyrus (MFG), and several regions of temporal neocortex. However, the correlations were all in the negative direction; better memory performance was associated with smaller volumes. Several previous reports of significant negative correlations between gray matter volumes and memory performance are described, so that the possible reasons for this surprising finding are discussed.

Mapping cortical thickness and gray matter concentration in first episode schizophrenia

We mapped regional changes in cortical thickness and intensity-based cortical gray matter concentration in first episode schizophrenia. High-resolution magnetic resonance images were obtained from 72 (51 male, 21 female) first episode patients and 78 (37 male, 41 female) healthy subjects similar in age. Cortical pattern matching methods allowed comparisons of cortical thickness and gray matter concentration at thousands of homologous cortical locations between subjects in three dimensions. Principal components analyses reduced measures obtained across the cortex to identify global differences in cortical thickness/gray matter concentration. First principal component factor scores showed significant effects of diagnosis, sex and age for both cortical measures. Diagnosis and age effects remained significant after brain size correction. Cortical thickness and gray matter concentration values were highly correlated. Statistical maps showed significant regional gray matter thinning in frontal, temporal and parietal heteromodal association cortices bilaterally in first episode patients. Regional reductions in cortical gray matter concentration were similar but pronounced in the superior temporal lobe. Regional reductions in cortical thickness and gray matter concentration are present at disease onset in brain regions linked with functional disturbances in schizophrenia. Cortical thickness and gray matter concentration mapping produce similar results, although the concentration metric may be influenced by diagnostic differences in extra-cortical cerebrospinal fluid and surface curvature/complexity.

Comparison of sustained and transient activity in children and adults using a mixed blocked/event-related fMRI design

The ability to make direct comparisons between adult and child neuroimaging data is important to the study of the neural basis of cognitive development. Recent fMRI studies in adults have used mixed blocked/event-related designs to extract activity consistent with separable sustained, task-related processes and transient, trial-related processes. Because brain regions with different time courses of activity may have different roles in cognitive processing, the ability to distinguish between sustained and transient signals would contribute to understanding the functional roles of regions involved in cognitive processing. The developmental profile of such activity would give insight into how cognitive processing develops over time. The purpose of this study was to assess the utility of the mixed design to detect and dissociate sustained and transient activity in children, and to determine if the time courses or magnitudes of the extracted signals differ from those extracted from adults. An fMRI experiment was performed on 10 adults and 10 children (ages 7-8) using counterphase flickering checkerboard stimuli that produced sustained, transient, and a combination of sustained and transient responses in visual cortex. Analyses were performed using the general linear model (GLM) assuming a shape for sustained effects, but not for transient effects. In visual cortex, neither transient nor sustained effects showed significant between-group differences. For both groups, flickering checkerboard stimuli produced robust responses in visual cortex contralateral but not ipsilateral to the stimulus. Results extend the feasibility of direct statistical comparison of adults and children; mixed designs provide a means to examine neural activity in both adults and children related to sustained, task-level processes, likely related to task-level control.

Cognitive correlates of white matter growth and stress hormones in female squirrel monkey adults

Neurobiological studies of stress and cognitive aging seldom consider white matter despite indications that complex brain processes depend on networks and white matter interconnections. Frontal and temporal lobe white matter volumes increase throughout midlife adulthood in humans, and this aspect of aging is thought to enhance distributed brain functions. Here, we examine spatial learning and memory, neuroendocrine responses to psychological stress, and regional volumes of gray and white matter determined by magnetic resonance imaging in 31 female squirrel monkeys between the ages of 5 and 17 years. This period of lifespan development corresponds to the years 18-60 in humans. Older adults responded to stress with greater increases in plasma levels of adrenocorticotropic hormone and modest reductions in glucocorticoid feedback sensitivity relative to young adults. Learning and memory did not differ with age during the initial cognitive test sessions, but older adults more often failed to inhibit the initial learned response after subsequent spatial reversals. Impaired cognitive response inhibition correlated with the expansion of white matter volume statistically controlling for age, stress hormones, gray matter, and CSF volumes. These results indicate that instead of enhancing cognitive control during midlife adulthood, white matter volume expansion contributes to aspects of cognitive decline. Cellular and molecular research combined with brain imaging is needed to determine the basis of white matter growth in adults, elucidate its functions during lifespan development, and provide potential new targets for therapies aimed at maintaining in humans cognitive vitality with aging.

Aging, sexual dimorphism, and hemispheric asymmetry of the cerebral cortex: replicability of regional differences in volume

We examined age-, sex-, and hemisphere-related differences in the cerebral cortex. Volumes of the cerebral hemispheres and 13 regions of interest (ROIs) were measured on magnetic resonance images of 200 healthy adults. The strength of association between age and volume differed across ROIs. The lateral prefrontal cortex exhibited the greatest age-related differences, whereas significantly weaker associations were observed in the prefrontal white matter, sensory-motor, and visual association regions. The hippocampal shrinkage was significant in people in their mid-fifties. The primary visual, anterior cingulate, the inferior parietal cortices, and the parietal white matter showed no age-related differences. The pattern of age-related regional differences replicated the findings previously obtained on an independent sample drawn from the same population. Men evidenced larger volumes in all ROIs except the inferior parietal lobule, even after sexual dimorphism in body size was statistically controlled. In some regions (hippocampus and fusiform gyrus) men exhibited steeper negative age-related trends than women. Although a typical pattern of global hemispheric asymmetry was observed, the direction and magnitude of regional volumetric asymmetry was as inconsistent as in the previous reports. Thus, a pattern of age-related shrinkage suggesting increased vulnerability of the lateral prefrontal cortex to aging appears stable and replicable, whereas little consistency exists in sex-related and hemispheric differences in regional cortical volumes.

Adolescence and the Trajectory of Alcohol Use: Basic to Clinical Studies

Emerging findings from developmentally focused research indicates subtle but important neurocognitive disadvantages among adolescents with alcohol-use disorders (AUD) as compared to teens without AUD. Even after 3 weeks of abstinence AUD youth display a 10% decrement in delayed memory functions. Neuropsychological testing of youth followed at 4 and 8 years demonstrates that heavy drinking during adolescence is associated with diminished retrieval of verbal and nonverbal material, and poorer performance on tests requiring attention skills. Alcohol withdrawal over the teen years appears to uniquely contribute to deterioration in functioning in visuospatial tasks. Brain imaging studies suggest reduced hippocampal volumes, white matter microstructure irregularities, brain response abnormalities while performing challenging cognitive tasks, and enhanced brain response when viewing alcohol cues (i.e., alcohol advertisements) among adolescents with AUD. Family characteristics such as history of alcoholism and socioeconomic status as well as personal features, including adolescent psychopathology, gender, and age of onset must be carefully considered when investigating the influence of teenage drinking on neurocognition. Further research is needed to understand how age at onset of drinking and duration of abstinence at the time of assessment affect cognitive findings. Longitudinal studies are needed to clarify neuromaturational changes associated with early alcohol exposure and patterns of resiliency. Although the magnitude of alcohol-related effects observed in adolescents' neurocognition is relatively modest, the implications are major given the prevalence of alcohol involvement, and the important educational, occupational, and social transitions that occur during adolescence.

Voxel-based morphometry in adolescents with bipolar disorder: first results

Bipolar disorder is an increasingly recognized cause of significant morbidity in the pediatric age group. However, there is still a large degree of uncertainty regarding the underlying neurobiological deficits. In this preliminary study, we performed automated volumetric studies and whole-brain voxel-based morphometry (VBM) on gray matter. Imaging data from 10 adolescents with bipolar disorder were compared with data from 52 age- and gender-matched healthy controls. Previously defined brain parcellations and optimized VBM protocols were used, based on custom-made pediatric reference data. An additional, exploratory whole-brain comparison was also implemented. The volumetric region-of-interest study revealed significantly greater gray matter volume in central gray matter structures bilaterally (including the basal ganglia and the thalamus) and the left temporal lobe in the bipolar group. VBM confirmed bilaterally larger basal ganglia. Localized gray matter deficits in bipolar subjects were found in the medial temporal lobe, orbito-frontal cortex, and the anterior cingulate, confirming and extending earlier studies.

Voxel-based morphometry of human brain with age and cerebrovascular risk factors

The objectives of this study were to evaluate the correlations of the volumes of the gray matter and white matter with age, and the correlations of the tissue probabilities of the gray matter and white matter with age and several cerebrovascular risk factors. We obtained magnetic resonance (MR) images of the brain and clinical information from 769 normal Japanese subjects. We processed the MR images automatically by correcting for inter-individual differences in brain size and shape, and by segmenting the MR images into the gray matter and white matter. Volumetry of the brain revealed a significant negative correlation between the gray matter volume and age, which was not observed between white matter volume and age. Voxel-based morphometry showed that age, systolic blood pressure, and alcohol drinking correlated with the regional tissue probabilities of the gray matter and white matter.

Diffusion tensor imaging of adult age differences in cerebral white matter: relation to response time

Diffusion tensor imaging (DTI) measures the displacement of water molecules across tissue components, thus providing information regarding the microstructure of cerebral white matter. Fractional anisotropy (FA), the degree to which diffusion is directionally dependent, is typically higher for compact, homogeneous fiber bundles such as the corpus callosum. Previous DTI studies in adults have demonstrated an age-related decline in white matter FA, but whether the relation between FA and behavioral performance varies as a function of age has not been determined. We investigated adult age differences in FA, and age-related changes in the relation between FA and response time (RT), in a visual target-detection task. The results confirmed that, independently of age, FA is higher in the corpus callosum than in other brain regions. We also observed an age-related decline in FA that did not vary significantly across the brain regions. For both age groups, a lower level of integrity of the cerebral white matter (as indexed by FA), in specific brain regions, was associated with slower responses in the visual task. An age-related change in this relation was evident, however, in that the best predictor of RT for younger adults was FA in the splenium of the corpus callosum, whereas for older adults the best predictor was FA in the anterior limb of the internal capsule. This pattern is consistent with measures of the task-related cortical activation obtained from these same individuals and suggests an age-related increase in the attentional control of responses mediated by corticostriatal or corticothalamic circuits.

Cerebral volume loss, cognitive deficit and neuropsychological performance: comparative measures of brain atrophy: I. Dementia

There are several magnetic resonance (MR) imaging methods to measure brain volume and cerebral atrophy; however, the best measure for examining potential relationships between such measures and neuropsychological performance has not been established. Relationships between seven measures of MR derived brain volume or indices of atrophy and neuropsychological performance in the elderly subjects of the population-based Cache County, Utah Study of Aging and Memory (n = 195) were evaluated. The seven MR measures included uncorrected total brain volume (TBV), TBV corrected by total intracranial volume (TICV), TBV corrected by the ratio of the individuals TICV by group TICV (TBVC), a ventricle-to-brain ratio (VBR), total ventricular volume (TVV), TVV corrected by TICV, and a measure of parenchymal volume loss. The cases from the Cache County Study were comprised of elderly individuals classified into one of four subject groups based on a consensus diagnostic process, independent of quantitative MR imaging findings. The groups included subjects with Alzheimer's disease (AD, n = 85), no dementia but mild/ambiguous (M/A) deficits (n = 30), a group of subjects with non-AD dementia or neuropsychiatric disorder including vascular dementia (n = 60), and control subjects (n = 20). Neuropsychological performance was based on the Mini-Mental Status Exam (MMSE) and an expanded neuropsychological test battery (consortium to establish a registry for Alzheimer's disease (CERAD). The results demonstrated that the various quantitative MR measures were highly interrelated and no single measure was statistically superior. However, TBVC, TBV/TICV and VBR consistently exhibited the more robust relationships with neuropsychological performance. These results suggest that a single corrected brain volume measure or index is sufficient in studies examining global MR indicators of cerebral atrophy in relation to cognitive function and recommends use of either TBVC, TBV/TICV, or VBR.

Incentive-elicited brain activation in adolescents: similarities and differences from young adults

Brain motivational circuitry in human adolescence is poorly characterized. One theory holds that risky behavior in adolescence results in part from a relatively overactive ventral striatal (VS) motivational circuit that readily energizes approach toward salient appetitive cues. However, other evidence fosters a theory that this circuit is developmentally underactive, in which adolescents approach more robust incentives (such as risk taking or drug experimentation) to recruit this circuitry. To help resolve this, we compared brain activation in 12 adolescents (12-17 years of age) and 12 young adults (22-28 years of age) while they anticipated the opportunity to respond to obtain monetary gains as well as to avoid monetary losses. In both age groups, anticipation of potential gain activated portions of the VS, right insula, dorsal thalamus, and dorsal midbrain, where the magnitude of VS activation was sensitive to gain amount. Notification of gain outcomes (in contrast with missed gains) activated the mesial frontal cortex (mFC). Across all subjects, signal increase in the right nucleus accumbens during anticipation of responding for large gains independently correlated with both age and self-rated excitement about the high gain cue. In direct comparison, adolescents evidenced less recruitment of the right VS and right-extended amygdala while anticipating responding for gains (in contrast with anticipation of nongains) compared with young adults. However, brain activation after gain outcomes did not appreciably differ between age groups. These results suggest that adolescents selectively show reduced recruitment of motivational but not consummatory components of reward-directed behavior.

Indirect evidence for early widespread gray matter involvement in relapsing–remitting multiple sclerosis

Multiple sclerosis (MS) has traditionally been viewed as an inflammatory demyelinating white matter (WM) disease of the central nervous system. However, recent pathology and MRI studies have shown lesions in the gray matter (GM) as well. To ascertain the extent of GM involvement, we obtained with nonlocalizing proton MR spectroscopy the concentration of N-acetylaspartate (NAA), a metabolite found almost exclusively in neuronal cells, T2-lesion loads, and GM and WM fractions in the entire brain of 71 relapsing-remitting (RR) MS patients (51 women, 20 men, 25-55 years old) and 41 healthy controls (27 women, 14 men, 23-55 years old). The average whole-brain NAA (WBNAA) difference between the patients and the controls was -2.9 mM (-22%, P < 0.0001); range: +1.2 to -7.8 mM (+8% to -63%). The patients' median T2 lesion volume was 5.5 (range: 0.140-28) cm(3). GM and WM comprised 50.4 +/- 3.8% and 30.4 +/- 5.0% (mean +/- standard deviation), respectively, of the total brain volume in the patients; 53.8 +/- 3.7% and 35.4 +/- 4.7% in the controls. Because WM and GM constitute approximately 40% and 60% of the brain parenchyma, respectively, and the NAA concentration in the former is 2/3 of the latter, WBNAA loss greater than 40% x 2/3 = 27% cannot be explained in terms of WM (axonal) pathology alone and must include widespread GM (neuronal) deficits. Therefore, the concept of MS, even at its earlier stages, as a WM disease might need to be reexamined.

Effects of age and sex on volumes of the thalamus, pons, and cortex

Volumes of thalamus, pons, cortical gray matter, and white matter were derived from MR brain images of healthy men and women spanning the adult age range in order to delineate patterns of aging and to compare age and sex effects in thalamus and pons with such effects in cortical gray and white matter volumes. Men had larger intracranial volume (ICV) than women, but ICV did not correlate with age in either sex. Thalamic, pontine, and cortical white matter volumes did not differ between men and women once ICV differences were taken into account, but men had more cortical gray matter than women even after accounting for ICV. Volumes of pons and thalamus were associated, independent of ICV, in women but not in men. Thalamic volume declined linearly with age at a similar rate in both men and women, whereas cortical gray matter volume declined more steeply with age in men than women. Both pontine and cortical white matter volumes remained stable across the age span in both men and women.

Age-related decline in striatal volume in rhesus monkeys: assessment of long-term calorie restriction

Using magnetic resonance imaging (MRI), we measured striatal volume in 22 male rhesus monkeys undergoing calorie restriction (CR) for 11-13 years and 38 monkeys who were fed ad libitum (CON). CR delays the onset of many age-related processes, and this study tested whether it would alter the age-related decline in striatal volume. The CON and CR groups were sub-divided into middle age (less than 24 years old) and old age groups. Contrary to expectation, volumes of the putamen (not the caudate nucleus) were larger bilaterally in the CON than in the CR group both at middle age and senescence. Regression analysis (region volume versus age) indicated bilateral age-related declines in putamen and caudate nucleus volumes in the old CON monkeys, but only for the putamen in the old CR monkeys. Because tests for slopes found no differences between the groups, the data do not establish an effect of CR. Further study, involving sequential imaging, is warranted in order to clarify the possible effects of CR on age-related changes in striatal volume.

Outcome classification of preschool children with autism spectrum disorders using MRI brain measures

OBJECTIVE

To test the hypothesis that a combination of magnetic resonance imaging (MRI) brain measures obtained during early childhood distinguish children with autism spectrum disorders (ASD) from typically developing children and is associated with functional outcome.

METHOD

Quantitative MRI technology was used to measure gray and white matter volumes (cerebrum and cerebellum), total brain volume, and the area of the cerebellar vermis in 52 boys with a provisional diagnosis of autism (aged 1.9-5.2 years) and 15 typically developing young children (aged 1.7-5.2 years). Diagnostic confirmation and cognitive outcome data were obtained after the children reached 5 years of age.

RESULTS

A discriminant function analysis of the MRI brain measures correctly classified 95.8% of the ASD cases and 92.3% of the control cases. This set of variables also correctly classified 85% of the ASD cases as lower functioning and 68% of the ASD cases as higher functioning.

CONCLUSIONS

These results indicate that variability in cerebellar and cerebral size is correlated with diagnostic and functional outcome in very young children with ASD.

Relationship between hippocampal volume and memory ability in healthy individuals across the lifespan: review and meta-analysis

Poor memory ability and small hippocampal volume measurements in magnetic resonance images co-occur in neurological patients. Numerous studies have examined the relationship between memory performance and hippocampal volumes in participants without neurological or psychiatric disorders, with widely varying results. Three hypotheses about volume-memory relationships in the normal human brain are discussed: "bigger is always better", a neuropsychological view that volume decreases due to normal aging are accompanied by memory decline, and a developmental perspective that regressive events in development may result in negative correlations between hippocampal volume and memory ability. Meta-analysis of results from 33 studies led to little support for the bigger-is-better hypothesis. A negative relationship between hippocampal volume and memory (smaller is better) was significant for studies with children, adolescents, and young adults. For studies with older adults, the most striking observation was extreme variability: the evidence for a positive relationship between hippocampal size and episodic memory ability in older adults was surprisingly weak. Some of the variability in results from older adults was associated with statistical methods of normalizing for age and head size, which are discussed.

Differential age-related changes in the regional metencephalic volumes in humans: a 5-year follow-up

We examined changes in the metencephalon of healthy adults who underwent magnetic resonance imaging twice, 5 years apart. The volumes of the cerebellar hemispheres, anterior and posterior vermis, declive-folium-tuber of the vermis, and the ventral pons were measured by operators unaware of subjects' characteristics and the time of scan. The cerebellar hemispheres and the cerebellar vermis, but not the ventral pons, were smaller in older people at both measurements. Significant linear shrinkage was observed in all examined metencephalic regions. Annualized rate of shrinkage was the greatest in the cerebellar hemispheres, somewhat smaller in the vermis, and minimal in the pons. Neither sex differences, nor sex-specific aging trends were found. We conclude that differential age-related shrinkage of the metencephalic structures occurs in healthy adults, but its magnitude differs from cross-sectional estimates.

Variability of gray and white matter during normal development: a voxel-based MRI analysis

This study was aimed at investigating regional and local variability of brain tissue during normal human brain development. We investigated high-resolution MR-imaging data using SPM99 (Wellcome Department, University College London, UK). A pixel-wise variation coefficient of gray and white matter was calculated to visualize local variability. Data from 200 normal children (5-18 years) were analyzed. We found a profound interaction between variability of brain structures and normal development in both gray and white matter. Variability in gray and white matter shows regionally specific, age-related variations, possibly offering a new tool for the assessment of subtle brain abnormalities. Our results emphasize the necessity to take this variability into account when planning pediatric neuroimaging studies.

Normative pediatric brain data for spatial normalization and segmentation differs from standard adult data

Spatial normalization and morphological studies of pediatric brain imaging data based on adult reference data may not be appropriate due to the developmental differences between the two populations. In this study, we set out to create pediatric templates and a priori brain tissue data from a large collection of normal, healthy children to compare it to standard adult data available within a widely used imaging software solution (SPM99, WDOCN, London, UK). Employing four different processing strategies, we found considerable differences between our pediatric data and the adult data. We conclude that caution should be used when analyzing pediatric brain data using adult a priori information. To assess the effects of using pediatric a priori brain information, the data obtained in this study is available to the scientific community from our website (www.irc.cchmc.org).

Effects of X-monosomy and X-linked imprinting on superior temporal gyrus morphology in Turner syndrome

BACKGROUND

Turner syndrome (TS) results from complete or partial monosomy X. The cognitive phenotype of TS involves preservation of verbal skills with visuospatial functioning deficits. The superior temporal gyrus (STG), which is involved in language capacities, has not been investigated in TS.

METHODS

The STG was measured in 30 female subjects (mean age = 14.73 +/- 6.41; range = 7.56-33.30) with TS and 30 age-matched control subjects (mean age = 14.63 +/- 5.90; range = 6.35-32.65) using volumetric magnetic resonance imaging analyses.

RESULTS

-Right STG, including both gray and white matter volumes, was significantly larger in TS compared with control subjects. Overall left STG volume was not significantly different between groups, although left white matter volume was increased in the TS subjects. The TS subgroup with a maternally derived X chromosome (Xm) demonstrated more aberrant STG volumes compared with subjects with a paternally (Xp) derived X and control subjects. The difference in STG volumes between Xm and control subjects involved both white and gray matter. The Xm subjects differed from Xp subjects only in terms of gray matter.

CONCLUSIONS

These findings suggest that X-monosomy and X-linked imprinting negatively affect STG development, possibly by disrupting neural pruning mechanisms.