Alterations in cortical thickness development in preterm-born individuals:Implications for high-order cognitive functions

AbstractVery preterm birth (gestational age <33weeks) is associated with alterations in cortical thickness and with neuropsychological/behavioural impairments. Here we studied cortical thickness in very preterm born individuals and controls in mid-adolescence (mean age 15years) and beginning of adulthood (mean age 20years), as well as longitudinal changes between the two time points. Using univariate approaches, we showed both increases and decreases in cortical thickness in very preterm born individuals compared to controls. Specifically (1) very preterm born adolescents displayed extensive areas of greater cortical thickness, especially in occipitotemporal and prefrontal cortices, differences which decreased substantially by early adulthood; (2) at both time points, very preterm-born participants showed smaller cortical thickness, especially in parahippocampal and insular regions. We then employed a multivariate approach (support vector machine) to study spatially discriminating features between the two groups, which achieved a mean accuracy of 86.5%. The spatially distributed regions in which cortical thickness best discriminated between the groups (top 5%) included temporal, occipitotemporal, parietal and prefrontal cortices. Within these spatially distributed regions (top 1%), longitudinal changes in cortical thickness in left temporal pole, right occipitotemporal gyrus and left superior parietal lobe were significantly associated with scores on language-based tests of executive function. These results describe alterations in cortical thickness development in preterm-born individuals in their second decade of life, with implications for high-order cognitive processing

Prognostic value of cortically induced motor evoked activity by TMS in chronic stroke: caveats from a very revealing single clinical case

Background: We report the case of a chronic stroke patient (62 months after injury) showing total absence of motor activity evoked by transcranial magnetic stimulation (TMS) of spared regions of the left motor cortex, but near-to-complete recovery of motor abilities in the affected hand. Case presentation: Multimodal investigations included detailed TMS based motor mapping, motor evoked potentials (MEP), and Cortical Silent period (CSP) as well as functional magnetic resonance imaging (fMRI) of motor activity, MRI based lesion analysis and Diffusion Tensor Imaging (DTI) Tractography of corticospinal tract (CST). Anatomical analysis revealed a left hemisphere subinsular lesion interrupting the descending left CST at the level of the internal capsule. The absence of MEPs after intense TMS pulses to the ipsilesional M1, and the reversible suppression of ongoing electromyographic (EMG) activity (indexed by CSP) demonstrate a weak modulation of subcortical systems by the ipsilesional left frontal cortex, but an inability to induce efficient descending volleys from those cortical locations to right hand and forearm muscles. Functional MRI recordings under grasping and finger tapping patterns involving the affected hand showed slight signs of subcortical recruitment, as compared to the unaffected hand and hemisphere, as well as the expected cortical activations. Conclusions: The potential sources of motor voluntary activity for the affected hand in absence of MEPs are discussed. We conclude that multimodal analysis may contribute to a more accurate prognosis of stroke patients

Frontal networks in adults with autism spectrum disorder.

It has been postulated that autism spectrum disorder is underpinned by an 'atypical connectivity' involving higher-order association brain regions. To test this hypothesis in a large cohort of adults with autism spectrum disorder we compared the white matter networks of 61 adult males with autism spectrum disorder and 61 neurotypical controls, using two complementary approaches to diffusion tensor magnetic resonance imaging. First, we applied tract-based spatial statistics, a 'whole brain' non-hypothesis driven method, to identify differences in white matter networks in adults with autism spectrum disorder. Following this we used a tract-specific analysis, based on tractography, to carry out a more detailed analysis of individual tracts identified by tract-based spatial statistics. Finally, within the autism spectrum disorder group, we studied the relationship between diffusion measures and autistic symptom severity. Tract-based spatial statistics revealed that autism spectrum disorder was associated with significantly reduced fractional anisotropy in regions that included frontal lobe pathways. Tractography analysis of these specific pathways showed increased mean and perpendicular diffusivity, and reduced number of streamlines in the anterior and long segments of the arcuate fasciculus, cingulum and uncinate--predominantly in the left hemisphere. Abnormalities were also evident in the anterior portions of the corpus callosum connecting left and right frontal lobes. The degree of microstructural alteration of the arcuate and uncinate fasciculi was associated with severity of symptoms in language and social reciprocity in childhood. Our results indicated that autism spectrum disorder is a developmental condition associated with abnormal connectivity of the frontal lobes. Furthermore our findings showed that male adults with autism spectrum disorder have regional differences in brain anatomy, which correlate with specific aspects of autistic symptoms. Overall these results suggest that autism spectrum disorder is a condition linked to aberrant developmental trajectories of the frontal networks that persist in adult life

Alterations in development of hippocampal and cortical memory mechanisms following very preterm birth

Deficits in memory function have been described in children and adolescents who were born very preterm (VPT), which can have profound effects on their school achievement and everyday life. However, to date, little is known about the development of the neuroanatomical substrates of memory following VPT birth. Here we focus on episodic and working memory and highlight key recent functional and structural magnetic resonance imaging (MRI) studies that have advanced our understanding of the relationship between alterations seen in the VPT brain and typical neurodevelopment of networks supporting these memory functions. We contrast evidence from the episodic and working memory literatures and suggest that knowledge gained from these functional and neuroanatomical studies may point to specific time windows in which working memory interventions may be most effective

A whole-brain investigation of white matter microstructure in adolescents with conduct disorder

<div><p>Background</p><p>The biological basis of severe antisocial behaviour in adolescents is poorly understood. We recently reported that adolescents with conduct disorder (CD) have significantly increased fractional anisotropy (FA) of the uncinate fasciculus (a white matter (WM) tract that connects the amygdala to the frontal lobe) compared to their non-CD peers. However, the extent of WM abnormality in other brain regions is currently unclear.</p><p>Methods</p><p>We used tract-based spatial statistics to investigate whole brain WM microstructural organisation in 27 adolescent males with CD, and 21 non-CD controls. We also examined relationships between FA and behavioural measures. Groups did not differ significantly in age, ethnicity, or substance use history.</p><p>Results</p><p>The CD group, compared to controls, had clusters of significantly greater FA in 7 brain regions corresponding to: 1) the bilateral inferior and superior cerebellar peduncles, corticopontocerebellar tract, posterior limb of internal capsule, and corticospinal tract; 2) right superior longitudinal fasciculus; and 3) left cerebellar WM. Severity of antisocial behavior and callous-unemotional symptoms were significantly correlated with FA in several of these regions across the total sample, but not in the CD or control groups alone.</p><p>Conclusions</p><p>Adolescents with CD have significantly greater FA than controls in WM regions corresponding predominantly to the fronto-cerebellar circuit. There is preliminary evidence that variation in WM microstructure may be dimensionally related to behaviour problems in youngsters. These findings are consistent with the hypothesis that antisocial behaviour in some young people is associated with abnormalities in WM ‘connectivity’.</p></div

Repeating with the right hemisphere: reduced interactions between phonological and lexical-semantic systems in crossed aphasia?

Journal Article;Knowledge on the patterns of repetition amongst individuals who develop language deficits in association with right hemisphere lesions (crossed aphasia) is very limited. Available data indicate that repetition in some crossed aphasics experiencing phonological processing deficits is not heavily influenced by lexical-semantic variables (lexicality, imageability, and frequency) as is regularly reported in phonologically-impaired cases with left hemisphere damage. Moreover, in view of the fact that crossed aphasia is rare, information on the role of right cortical areas and white matter tracts underpinning language repetition deficits is scarce. In this study, repetition performance was assessed in two patients with crossed conduction aphasia and striatal/capsular vascular lesions encompassing the right arcuate fasciculus (AF) and inferior frontal-occipital fasciculus (IFOF), the temporal stem and the white matter underneath the supramarginal gyrus. Both patients showed lexicality effects repeating better words than non-words, but manipulation of other lexical-semantic variables exerted less influence on repetition performance. Imageability and frequency effects, production of meaning-based paraphrases during sentence repetition, or better performance on repeating novel sentences than overlearned clichés were hardly ever observed in these two patients. In one patient, diffusion tensor imaging disclosed damage to the right long direct segment of the AF and IFOF with relative sparing of the anterior indirect and posterior segments of the AF, together with fully developed left perisylvian white matter pathways. These findings suggest that striatal/capsular lesions extending into the right AF and IFOF in some individuals with right hemisphere language dominance are associated with atypical repetition patterns which might reflect reduced interactions between phonological and lexical-semantic processes.Ye

Relationship between receptor covariance and functional connectivity in macaque somatosensory areas

Introduction:Sensory information is processed in a hierarchical way across different areas of the somatosensory cortex. In primates, the sensory signal first arrives at the primary somatosensory cortex (SI), and then at the secondary somatosensory cortex (SII), finally at the association cortex, which consists of areas that are located on the superior (SPL), inferior parietal lobes (IPL), and intraparietal sulcus (ips). Neurotransmitter receptors are a key element of information processing. To understand how somatosensory information is processed between brain areas, we analyzed the multiple receptor covariance (RC) patterns of distinct somatosensory areas. Furthermore, we examined functional connectivity (FC) patterns of each area and explore the shared and specific characteristics between RC and FC.Methods:In the present study, we defined 118 areas throughout the macaque brain, 36 of which are somatosensory-related areas located within SI, SII, and parietal association areas. The densities of 14 different receptors in each of the 118 areas had been quantified by means of in vitro receptor autoradiography. To construct the RC of each somatosensory-related area with the remaining areas across the cortex, we calculated a representative feature vector consisting of 14 receptor densities for each area. Statistical similarity between two areas was measured by computing the Pearson correlation. Furthermore, we reconstructed the resting-state FC of the somatosensory cortex using fMRI data from the PRIME-DE dataset. A principal components analysis was performed on the BOLD activity time courses across all vertices within each area, where the first principal component was taken as the representative activity time course for this area. The representative time courses were subsequently correlated with the activity time courses for each vertex across the brain.Results:RC patterns are similar for areas that are 1) anatomically adjacent to each other; or 2) at the same level of hierarchical organization. All SI areas showed consistent correlations with caudal SII, rostral and ventral ips, rostral IPL and higher visual areas. SII areas displayed stronger correlations with rostroventral IPL and cingulate areas, but relatively weaker correlations with ips and visual areas. Regarding SPL, there is a clear segregation between areas located on the lateral surface and the areas located within the cingulate sulcus. Within IPL and ips, the RC patterns changed gradually from rostral to caudal. As in RC patterns, the strongest FC was found between neighbouring areas. Likewise, early and higher sensory areas could also be separated by their FC patterns. The FC and RC also have some differences. For example, FC patterns of SI show more consistent connections to the primary motor cortex instead of to higher visual areas.Conclusions:Our results show that areas belonging to SI, SII or the somatosensory association cortex have distinct connectivity patterns in both RC and FC. Furthermore, despite comparable features, there are also important differences between the RC and FC of the somatosensory cortex. More broadly, our findings provide a link between the chemoarchitectonic and functional organization of the macaque somatosensory cortex and thus a novel direction for a multiscale understanding of brain structure and function

Interindividual Variability of Functional Connectivity in Awake and Anesthetized Rhesus Macaque Monkeys

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