Mapping the development of white matter tracts with diffusion tensor imaging

In this study, the development of white matter was studied using an optimized diffusion tensor imaging (DTI) protocol in 20 normal subjects (10–40 years old). The normal development of white matter tracts was addressed by comparing the diffusion anisotropy results between two sub‐groups: eight adults (26–38 years old) and eight adolescents (13–15 years old). The difference in myelination extent between these two groups as indexed by the fractional anisotropy was identified by conducting a student t‐test of the measured diffusion anisotropy maps. Significant differences (p < 0.01) were detected in the gyrus frontalis medialis (GFM), gyrus temporalis medialis (GTM) and gyrus cinguli (GC), in addition to the developmental changes in corpus callosum. A brief overview of previous published DTI studies in developmental science and current progress in DTI techniques is also given at the end of this paper. It may be useful for readers interested in using DTI to study developmental problems but who are not familiar with the various technical aspects.     

Fiber tracking using magnetic resonance diffusion tensor imaging and its applications to human brain development

Diffusion tensor imaging is unique in its ability to noninvasively visualize white matter fiber tracts in the human brain in vivo. Diffusion is the incoherent motion of water molecules on a microscopic scale. This motion is itself dependent on the micro-structural environment that restricts the movement of the water molecules. In white matter fibers there is a pronounced directional dependence on diffusion. With white matter fiber tracking or tractography, projections among brain regions can be detected in the three-dimensional diffusion tensor dataset according to the directionality of the fibers. Examples of developmental changes in diffusion, tracking of major fiber tracts, and examples of how diffusion tensor tractography and functional magnetic resonance imaging can be combined are provided. These techniques are complimentary and allow both the identification of the eloquent areas of the brain involved in specific functional tasks, and the connections between them. The noninvasive nature of magnetic resonance imaging will allow these techniques to be used in both longitudinal developmental and diagnostic studies. An overview of the technique and preliminary applications are presented, along with its current limitations.     

Structural brain abnormalities in the major psychoses: a quantitative review of the evidence from computerized imaging

The neuroimaging literature on structural brain abnormalities in the major psychoses is quantitatively reviewed. The mean effect size for studies of lateral ventriculomegaly in schizophrenia (d = .70) corresponded to 43% nonoverlap between the distributions of schizophrenics and control Ss. Planimetry yielded larger effects than linear methods of ventricular size estimation. Although enlargement of the third ventricle was comparable to that of lateral ventriculomegaly (d = .66), it was found to be significantly greater after differences in measurement method were taken into account. The average cumulative length of hospitalization, adjusted for patients' age and duration of illness, predicted ventriculomegaly in schizophrenia. Studies on schizophrenia and affective disorder differed neither in the extent of reported ventriculomegaly nor in the amount of "cortical atrophy."     

ELSI priorities for brain imaging

As one of the most compelling technologies for imaging the brain, functional MRI (fMRI) produces measurements and persuasive pictures of research subjects making cognitive judgments and even reasoning through difficult moral decisions. Even after centuries of studying the link between brain and behavior, this capability presents a number of novel significant questions. For example, what are the implications of biologizing human experience? How might neuroimaging disrupt the mysteries of human nature, spirituality, and personal identity? Rather than waiting for an ethical agenda to emerge from some unpredictable combination of the concerns of ethicists and researchers, the attention of journalists, or after controversy is sparked by research that cannot be retracted, we queried key figures in bioethics and the humanities, neuroscience, media, industry, and patient advocacy in focus groups and interviews. We identified specific ethical, legal and social issues (ELSI) that highlight researcher obligations and the nonclinical impact of the technology at this new frontier.     

Self-representation and brain development

This study examined the relation between self-representation and brain development in infants and young children. Self-representation was assessed by mirror recognition, personal pronoun use, and pretend play. Structural brain images were obtained from magnetic resonance imaging (MRI). Brain development was assessed by a quantitative measure of maturation of the temporo-parietal junction, temporal pole, medial frontal cortex, and occipital cortex. Fifteen children (15 to 30 months of age; 3 girls) without MRI abnormalities were assessed. Only maturation of the left temporo-parietal junction was related to self-representation after controlling for age. These findings provide some evidence that brain maturation is related to the emergence of a representation of self in the human child.     

Early lexical development in children with focal brain injury

Early lexical development in 27 children with focal brain injury was studied cross-sectionally and longitudinally. Data were obtained from children between 12 and 35 months of age who acquired their lesion prenatally or within the first 6 months of life. Results for the group as a whole provide clear evidence for delays in lexical comprehension and production, and for a larger number of comprehension/production dissociations than would be expected by chance. In addition, a significant number of children were observed having unusual difficulty mastering predication and/or using an atypically high proportion of closed class words (suggesting reliance on holistic/formulaic speech). Analyses by lesion type revealed no effect of lesion size. Analyses according to side of lesion revealed that children with right-hemisphere damage produced a higher proportion of closed class words, suggesting heavy reliance on well-practiced but under-analyzed speech formulae. Children with left-hemisphere damage were slightly better in comprehension than children with right-hemisphere damage. In addition, left posterior lesions were associated with greater delays in expressive language, and delays were more protracted in children with left posterior damage. No differential effects of left posterior damage were found for lexical comprehension.     

Functional brain imaging of childhood clinical disorders with PET and SPECT

During the first years of life, the human brain undergoes repetitive modifications in its anatomical, functional and synaptic construction to reach the complex functional organization of the adult central nervous system. Over the last decade, positron emission tomography (PET) and single photon emission computed tomography (SPECT) have provided further insight into these maturation processes. This article reviews clinical and research applications of PET and SPECT in childhood disorders, with an emphasis on the specific contribution of these techniques in improving our knowledge about the pathophysiology of the developing brain.     

Cognitive impairment and whole brain diffusion in patients with neuromyelitis optica after acute relapse

The objective of this study investigated cognitive impairments and their correlations with fractional anisotropy (FA) and mean diffusivity (MD) in patients with neuromyelitis optica (NMO) without visible lesions on conventional brain MRI during acute relapse. Twenty one patients with NMO and 21 normal control subjects received several cognitive tests to assess cognitive function. Head diffusion tensor imaging (DTI) of all patients with NMO were collected with a 3-T MR system. Correlations of cognitive test scores and whole brain FA and MD were examined by voxel-based analysis. Region-of-interest analysis was applied to the significantly correlated regions which the most frequently appeared. We found that NMO patients without visible brain lesions had significantly impaired learning and memory, decreased information processing speed, and damaged attention compared with normal control subjects. These impaired cognitive domains were significantly correlated with FA and MD in local regions of corpus callosum, anterior cingulate and medial frontal cortex. In corpus callosum of NMO patients, mean FA was significantly lower and mean MD higher than normal control subjects. Our findings suggest that cognitive impairments in learning and memory, information processing speed and attention occur in NMO patients without visible brain lesions during acute relapse. The impairments in immediate and short-term memory in NMO patients may be due to information encoding deficits in the process of information acquisition. The corpus callosum of such patients may have local microscopic damages that play a role in cognitive impairments during acute relapse.     

A space for measuring mind and brain: interdisciplinarity and digital tools in the development of brain mapping and functional imaging, 1980-1990

Brain mapping is said to have opened up the possibility of a new collaboration between the sciences of mind and the sciences of the brain, potentially leading to a new kind of scientist, sometimes called "cognitive neuroscientist." This article traces the recent history of brain mapping and analyzes the processes that have led to a new "close working relationship" between the sciences of mind and brain. A key part of the working relationship is shown to be constituted through the development of the Talairach system, a digital space in which to measure structure and function. The development of meaningful brain mapping data involves the creation of measurement spaces that allow interdisciplinary collaboration and is not the result solely of theoretical developments or of the application of a technology.     

Self-organizing individual differences in brain development

Brain development is self-organizing in that the unique structure of each brain evolves in unpredictable ways through recursive modifications of synaptic networks. In this article, I review mechanisms of neural change in real time and over development, and I argue that change at each of these time scales embodies principles of self-organizing systems. I demonstrate how corticolimbic configurations that emerge within occasions lay down synaptic structure across occasions, giving rise to individual trajectories that become entrenched with age. Emotions have a powerful influence on this process.This is because the neural processes mediating emotion consolidate patterns of activation across the brain, through their enhancement of inter-regional coordination in real time and their contribution to synaptic shaping over development. The loss of corticolimbic plasticity with age is an unfortunate fact of development, but it is compensated in part by transitional phases and individual learning experiences through which habits are modified or replaced. I emphasize variations in inter-systemic coupling as a key mediator of developing individual differences, and I discuss the acquisition of anxious/depressive appraisals as an example.     

The psychopath magnetized: insights from brain imaging

Psychopaths commit a disproportionate amount of violent crime, and this places a substantial economic and emotional burden on society. Elucidation of the neural correlates of psychopathy may lead to improved management and treatment of the condition. Although some methodological issues remain, the neuroimaging literature is generally converging on a set of brain regions and circuits that are consistently implicated in the condition: the orbitofrontal cortex, amygdala, and the anterior and posterior cingulate and adjacent (para)limbic structures. We discuss these findings in the context of extant theories of psychopathy and highlight the potential legal and policy implications of this body of work.     

Holonomic brain theory in imaging and object perception

Image processing in the visual system is described utilizing some basic neurophysiological data. We propose that both sensory and cognitive operations address features already conjoined in critical receptive fields. As both sensory perception and further processing stages are critically dependent upon movement, the theory emphasizes sensory-motor reciprocity in imaging and in object perception.     

White matter development during adolescence as shown by diffusion MRI

Previous volumetric developmental MRI studies of the brain have shown white matter development continuing through adolescence and into adulthood. This review presents current findings regarding white matter development and organization from diffusion MRI studies. The general trend during adolescence (age 12–18 years) is towards increasing fractional anisotropy (FA) with age and decreasing mean diffusivity (MD) with age, findings primarily due to decreasing radial diffusivity with age. However, results of studies vary as to the regional specificity of such age-related changes, likely due in part to methodological issues. Another general trend is for FA to positively correlate and MD to negatively correlate with cognitive function. This trend is however region-specific, task-specific, and population-specific; some studies have in fact found negative correlations of FA and positive correlations of MD in specific regions with specific measures of cognitive performance. There are also published reports of sexual dimorphism in white matter development, indicating differing developmental trajectories between males and females as well as differing relationships developmentally between white matter architecture and cognitive function. There is a need for more research to further elucidate the development of white matter and its relation to cognitive function during this critical developmental period.     

Language development after unilateral brain injury.

This longitudinal study describes the growth of syntactic abilities and vocabulary size in nine children with unilateral antepartum or perinatal brain injury. Five children with left hemisphere damage (LHD) and four with right hemisphere damage (RHD), ages 15 to 48 months, were evaluated on three or more occasions. Language samples generated from parent-child interaction were transcribed, coded, and analyzed using the Child Language Data Exchange System. Individual growth trajectories were constructed by graphing three dependent variables--MLU, scores on the Index of Productive Syntax (IPSYN), and number of different words--as a function of the child's age. One subject remained in a prelinguistic stage throughout the study. Simple linear functions best described the growth of MLU, IPSYN scores, and vocabulary in the other eight children. The slopes of the individual growth trajectories, the graphic representations of rates of progress, were comparable in the eight children. Seven children showed developmental delays in initial word use and five in the onset of multiword utterances. However, by age 24 months, four children with LHD and two children with RHD had syntactic capabilities comparable to those of children without brain injuries. The developmental patterns suggested that both cerebral hemispheres may play critical roles in the very earliest stages of language acquisition. Some unilateral lesions caused little discernible effect on language outcome in the toddler-preschool years after the initial developmental delays.     

Neural modeling,functional brain imaging,and cognition

The richness and complexity of data sets acquired from PET or fMRI studies of human cognition have not been exploited until recently by computational neural-modeling methods. In this article, two neural-modeling approaches for use with functional brain imaging data are described. One, which uses structural equation modeling, estimates the functional strengths of the anatomical connections between various brain regions during specific cognitive tasks. The second employs large-scale neural modeling to relate functional neuroimaging signals in multiple, interconnected brain regions to the underlying neurobiological time-varying activities in each region. Delayed match-to-sample (visual working memory for form) tasks are used to illustrate these models.