Combined analysis of DTI and fMRI data reveals a joint maturation of white and grey matter in a fronto-parietal network

The aim of this study was to explore whether there are networks of regions where maturation of white matter and changes in brain activity show similar developmental trends during childhood. In a previous study, we showed that during childhood, grey matter activity increases in frontal and parietal regions. We hypothesized that this would be mediated by maturation of white matter. Twenty-three healthy children aged 8-18 years were investigated. Brain activity was measured using the blood oxygen level-dependent (BOLD) contrast with functional magnetic resonance imaging (fMRI) during performance of a working memory (WM) task. White matter microstructure was investigated using diffusion tensor imaging (DTI). Based on the DTI data, we calculated fractional anisotropy (FA), an indicator of myelination and axon thickness. Prior to scanning, WM score was evaluated. WM score correlated independently with FA values and BOLD response in several regions. FA values and BOLD response were extracted for each subject from the peak voxels of these regions. The FA values were used as covariates in an additional BOLD analysis to find brain regions where FA values and BOLD response correlated. Conversely, the BOLD response values were used as covariates in an additional FA analysis. In several cortical and sub-cortical regions, there were positive correlations between maturation of white matter and increased brain activity. Specifically, and consistent with our hypothesis, we found that FA values in fronto-parietal white matter correlated with BOLD response in closely located grey matter in the superior frontal sulcus and inferior parietal lobe, areas that could form a functional network underlying working memory function.     

Neural pathways in tactile object recognition

OBJECTIVE: To define further the brain regions involved in tactile object recognition using functional MRI (fMRI) techniques. BACKGROUND: The neural substrates involved in tactile object recognition (TOR) have not been elucidated. Studies of nonhuman primates and humans suggest that basic motor and somatosensory mechanisms are involved at a peripheral level; however, the mechanisms of higher order object recognition have not been determined. METHODS: The authors investigated 11 normal volunteers utilizing fMRI techniques in an attempt to determine the neural pathways involved in TOR. Each individual performed a behavioral paradigm with the activated condition involving identification of objects by touch, with identification of rough/smooth as the control. RESULTS: Data suggest that in a majority of individuals, TOR involves the calcarine and extrastriatal cortex, inferior parietal lobule, inferior frontal gyrus, and superior frontal gyrus-polar region. CONCLUSIONS: TOR may utilize visual systems to access an internal object representation. The parietal cortices and inferior frontal regions may be involved in a concomitant lexical strategy of naming the object being examined. Frontal polar activation likely serves a role in visuospatial working memory or in recognizing unusual representations of objects. Overall, these findings suggest that TOR could involve a network of cortical regions subserving somatosensory, motor, visual, and, at times, lexical processing. The primary finding suggests that in this normal study population, the visual cortices may be involved in the topographic spatial processing of TOR.     

A dual-route perspective on poor reading in a regular orthography: An fMRI study

This study examined functional brain abnormalities in dyslexic German readers who - due to the regularity of German in the reading direction - do not exhibit the reading accuracy problem of English dyslexic readers, but suffer primarily from a reading speed problem. The in-scanner task required phonological lexical decisions (i.e., Does xxx sound like an existing word?) and presented familiar and unfamiliar letter strings of existing phonological words (e.g., Taxi-Taksi) together with nonwords (e.g., Tazi). Dyslexic readers exhibited the same response latency pattern (words < pseudohomophones < nonwords) as nonimpaired readers, but latencies to all item types were much prolonged. The imaging results were suggestive for a different neural organization of reading processes in dyslexic readers. Specifically, dyslexic readers, in response to lexical route processes, exhibited underactivation in a left ventral occipitotemporal (OT) region which presumably is engaged by visual-orthographic whole word recognition. This region was also insensitive to the increased visual-orthographic processing demands of the sublexical route. Reduced engagement in response to sublexical route processes was also found in a left inferior parietal region, presumably engaged by attentional processes, and in a left inferior frontal region, presumably engaged by phonological processes. In contrast to this reduced engagement of the optimal left hemisphere reading network (ventral OT, inferior parietal, inferior frontal), our dyslexic readers exhibited increased engagement of visual occipital regions and of regions presumably engaged by silent articulatory processes (premotor/motor cortex and subcortical caudate and putamen).     

Effect of word and syllable frequency on activation during lexical decision and reading aloud

This functional MRI (fMRI) study investigated the effect of lexical and syllable frequency on visual word processing during lexical decision and reading aloud. Previous research has shown a dissociation of syllable and word frequency effects in Spanish using behavioral and electrophysiological measures, suggesting that sublexical (syllabic) representations are computed and mediate the firing of lexical candidates. Here, we characterize the neuroanatomical basis of these lexical and sublexical manipulations and their dependence on task. During lexical decision, words with low vs. high lexical frequency increased activation in left frontal, anterior cingulate, supplemental motor area (SMA), and pre-SMA regions; while words with high vs. low syllable frequency increased activation in a left anterior inferior temporal region. In contrast, when the words were read aloud those with low vs. high syllable frequency increased activation in the left anterior insula, with no other significant effects. On the basis of the neuroanatomy, we propose that the contrasting effects of syllable frequency during lexical decision and reading aloud reflect two different cognitive processes in visual word processing. Specifically, words with high-frequency syllables may increase lexical competition in the inferior temporal lobe while facilitating articulatory planning in the left anterior insula.     

Chemotherapy‐induced structural changes in cerebral white matter and its correlation with impaired cognitive functioning in breast cancer patients

A subgroup of patients with breast cancer suffers from mild cognitive impairment after chemotherapy. To uncover the neural substrate of these mental complaints, we examined cerebral white matter (WM) integrity after chemotherapy using magnetic resonance diffusion tensor imaging (DTI) in combination with detailed cognitive assessment. Postchemotherapy breast cancer patients (n = 17) and matched healthy controls (n = 18) were recruited for DTI and neuropsychological testing, including the self‐report cognitive failure questionnaire (CFQ). Differences in DTI WM integrity parameters [fractional anisotropy (FA) and mean diffusivity (MD)] between patients and healthy controls were assessed using a voxel‐based two‐sample‐t‐test. In comparison with healthy controls, the patient group demonstrated decreased FA in frontal and temporal WM tracts and increased MD in frontal WM. These differences were also confirmed when comparing this patient group with an additional control group of nonchemotherapy‐treated breast cancer patients (n = 10). To address the heterogeneity observed in cognitive function after chemotherapy, we performed a voxel‐based correlation analysis between FA values and individual neuropsychological test scores. Significant correlations of FA with neuropsychological tests covering the domain of attention and processing/psychomotor speed were found in temporal and parietal WM tracts. Furthermore, CFQ scores correlated negatively in frontal and parietal WM. These studies show that chemotherapy seems to affect WM integrity and that parameters derived from DTI have the required sensitivity to quantify neural changes related to chemotherapy‐induced mild cognitive impairment. Hum Brain Mapp 32:480–493, 2011. © 2010 Wiley‐Liss, Inc.     

Brain networks of spatial awareness: evidence from diffusion tensor imaging tractography

Left unilateral neglect, a dramatic condition which impairs awareness of left-sided events, has been classically reported after right hemisphere cortical lesions involving the inferior parietal region. More recently, the involvement of long range white matter tracts has been highlighted, consistent with the idea that awareness of events occurring in space depends on the coordinated activity of anatomically distributed brain regions. Damage to the superior longitudinal fasciculus (SLF), linking parietal to frontal cortical regions, or to the inferior longitudinal fasciculus (ILF), connecting occipital and temporal lobes, has been described in neglect patients. In this study, four right-handed patients with right hemisphere strokes underwent a high definition anatomical MRI with diffusion tensor imaging (DTI) sequences and a pencil and paper neglect battery of tests. We used DTI tractography to visualise the SLF, ILF and the inferior fronto-occipital fasciculus (IFOF), a pathway running the depth of the temporal lobe, not hitherto associated with neglect. Two patients with cortical involvement of the inferior parietal and superior temporal regions, but intact and symmetrical fasciculi, showed no signs of neglect. The other two patients with signs of left neglect had superficial damage to the inferior parietal cortex and white matter damage involving the IFOF. These findings suggest that superficial damage to the inferior parietal cortex per se may not be sufficient to produce visual neglect. In some cases, a lesion to the direct connections between ventral occipital and frontal regions (ie, IFOF) may contribute to the manifestation of neglect by impairing the top down modulation of visual areas from the frontal cortex.     

Developmental changes in cerebral white matter microstructure in a disorder of lysosomal storage

The goal of this work was to study white matter (WM) integrity in children with cystinosis, a rare lysosomal storage disorder resulting in cystine accumulation in peripheral and central nervous system tissue. Based on previous reports of cystine crystal formation in myelin precursors as well as evidence for specific cognitive deficits in visuospatial functioning, diffusion tensor imaging (DTI) was applied to 24 children with cystinosis (age 3-7 years) and to 24 typically developing age-matched controls. Scalar diffusion indices, fractional anisotropy (FA) and mean diffusivity (MD), were examined in manually defined regions of interest within the parietal and inferior temporal lobes. Diffusion indices were correlated with performance on measures of visuospatial cognition and with white blood cell cystine levels. Bilaterally decreased FA and increased MD were evident in the inferior and superior parietal lobules in children with cystinosis, with comparable FA and MD to controls in inferior temporal WM, and implicate a dissociation of the dorsal and ventral visual pathways. In older cystinosis children (age > 5), diminutions in visuospatial performance were associated with reduced FA in the right inferior parietal lobule. In addition, increased MD was found in the presence of high cystine levels in all children with cystinosis. This study provides new information that the average diffusion properties in children with cystinosis deviate from typically developing children. Findings suggest the presence of early microstructural WM changes in addition to a secondary effect of cystine accumulation. These alterations may impact the development of efficient fiber networks important for visuospatial cognition.     

高功能孤独症患儿全脑白质纤维的弥散张量成像研究

目的 分析高功能孤独症患儿的全脑白质纤维的完整性.方法 对18例高功能孤独症患儿(病例组)以及10名年龄、性别、智商与病例组相匹配的健康儿童(对照组)进行全脑弥散张量成像(DTI)测量;应用基于体素的分析方法,比较两组全脑各向异性分数(FA)的差异.使用Spearman相关分析,分析病例组各感兴趣区FA值与儿章期孤独症评定表(CARS)总分及各项目之间的关系.结果 与对照组相比,病例组右侧额下回、左侧额中回及右侧颞下回邻近白质的FA值低(分别为0.67±0.10、0.57±0.09、0.50 ±0.12),左顶上小叶邻近白质的FA值高(0.55±0.15;P<0.001).病例组左额中回邻近白质的FA值与CARS中的与非生命物体的关系的得分呈负相关(r=-0.63,P=0.005).结论 高功能孤独症患儿多个部位的脑白质纤维的完整性受到破坏.     

Altered white matter integrity in primary restless legs syndrome patients: diffusion tensor imaging study

Abstract

Objectives:

A prior diffusion tensor imaging (DTI) of restless legs syndrome (RLS) subjects found alterations in brain white matter (WM). The aim of this study was to explore the possible mechanism of altered integrity of brain WM in RLS patients.

Methods:

The DTI measurement was performed in 22 subjects with RLS and 22 age-matched control subjects. Using a voxel-based analysis, fractional anisotropy (FA) and axial and radial diffusivities (AD and RD) were compared between RLS and control subjects with a two-sample t-test, and correlation analysis was performed in RLS subjects.

Results:

RLS subjects demonstrated decreased FA in the genu of the corpus callosum and frontal WM adjacent to the inferior frontal gyrus compared with the control subjects. For areas of decreased FA, both the AD and RD were higher than that in the control subjects.

Discussion:

Our findings suggest that loss of axonal density and myelin may account for WM changes seen in a prior study of RLS subjects.     

Quantification of age- and gender-related changes in diffusion tensor imaging indices in deep grey matter of the normal human brain

This study aimed to demonstrate age-related and gender-related changes in diffusion tensor imaging (DTI) indices of deep grey matter (GM) nuclei of the normal human brain. DTI was performed on 142 subjects (age: 10-52 years). Regions of interest were placed on the caudate nucleus (CN), putamen, globus pallidus, frontal white matter (WM), occipital WM, anterior and posterior limb of internal capsule, genu of the corpus callosum and splenium in all participants. The quadratic regression model was used to describe age-related and gender-related changes in DTI indices for GM and WM. We observed increased fractional anisotropy (FA) values with age up to adulthood in GM, and a rise up to the third decade of life followed by a decrease in FA for WM. We observed higher FA values in males compared to females in CN and all WM regions. Decreased mean diffusivity with age was observed in GM and WM irrespective of gender. This normative data may be valuable in the diagnosis of neurodegenerative diseases.