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Despite the important role of motor imagery (MI) in motor development, our understanding of the contribution of white matter fibre properties to MI performance in childhood remains limited. To provide novel insight into the white matter correlates of MI performance, this study examined the association between white matter fibre properties and motor imagery performance in a sample of typically developing children. High angular diffusion weighted imaging data were collected from 22 typically developing children aged 6-14 years (12 female, M Age = 10.56). Implicit motor imagery performance was assessed using a mental hand rotation paradigm. The cerebellar peduncles and the superior longitudinal fasciculus were reconstructed using TractSeg, a semi-automated method. For each tract, white matter microstructure (fibre density, FD) and morphology (fibre bundle cross-section, FC) were estimated using Fixel-Based Analysis. Permutation-based inference testing and partial correlation analyses demonstrated that higher FC in the middle cerebellar peduncles was associated with better MI performance. Tract-based region of interest analyses showed that higher FC in the middle and superior cerebellar peduncles were associated with better MI performance. Results suggest that white matter connectivity along the cerebellar peduncles may facilitate MI performance in childhood. These findings advance our understanding of the neurobiological systems that underlie MI performance in childhood and provide early evidence for the relevance of white matter sensorimotor pathways to internal action representations., (© 2024. The Author(s).)

Attention is a heterogeneous function theoretically divided into different systems. While functional magnetic resonance imaging (fMRI) has extensively characterized their functioning, the role of white matter in cognitive function has gained recent interest due to diffusion-weighted imaging advancements. However, most evidence relies on correlations between white matter properties and behavioral or cognitive measures. This study used a new method that combines the signal from distant voxels of fMRI images using the probability of structural connection given by high-resolution normative tractography. We analyzed three fMRI datasets with a visual perceptual task and three attentional manipulations: phasic alerting, spatial orienting, and executive attention. The phasic alerting network engaged temporal areas and their communication with frontal and parietal regions, with left hemisphere dominance. The orienting network involved bilateral fronto-parietal and midline regions communicating by association tracts and interhemispheric fibers. The executive attention network engaged a broad set of brain regions and white matter tracts connecting them, with a particular involvement of frontal areas and their connections with the rest of the brain. These results partially confirm and extend previous knowledge on the neural substrates of the attentional system, offering a more comprehensive understanding through the integration of structure and function., (© 2024. The Author(s).)

Diffusion tractography is a non-invasive technique that is being used to estimate the location and direction of white matter tracts in the brain. Identifying the characteristics of white matter plays an important role in research as well as in clinical practice that relies on finding the relationship between the structure and function of the brain. An Ising model implemented on a structural connectivity (SC) has proven to explain the spontaneous fluctuations in the brain at criticality using brain's structure depicted by white matter tracts. Since the SC is the only input of the model, identifying the tractography technique which provides a SC that delivers the highest prediction of the brain's intrinsic activity via the generalized Ising model (GIM) is essential. Hence an Ising model is simulated on SCs generated using two different acquisition schemes (single and multi-shell) and two different tractography approaches (deterministic and probabilistic) and analyzed at criticality across 69 healthy subjects. Results showed that by introducing the GIM, predictability of the empirical correlation matrix increases on average from 0.2 to 0.6 compared to the predictability using the empirical connectivity matrix directly. It is also observed that the SC generated using deterministic tractography without fractional anisotropy resulted in the highest correlation coefficient value of 0.65 between the simulated and empirical correlation matrices. Additionally, calculated dimensionalities per simulation illustrated that the dimensionality depends upon the method of tractography that has been used to extract the SC.

The prefrontal cortex (PFC) is a late developing region of the cortex, and its protracted maturation during adolescence may confer a period of plasticity. Closure of critical, or sensitive, periods in sensory cortices coincides with perineuronal net (PNN) expression, leading to enhanced inhibitory function and synaptic stabilization. PNN density has been found to increase across adolescence in the male rat medial PFC (mPFC). Here, we examined both male and female rats at four time points spanning adolescent development to stereologically quantify the number and intensity of PNNs in the mPFC. Additionally, because puberty coincides with broad behavioral and neuroanatomical changes, we collected tissue from age-matched pre- and post-pubertal siblings within a litter. Results indicate that both males and females show an increase in the total number and intensity of mPFC PNNs between postnatal day (P) 30 and P60. As we have previously found, white matter under the mPFC also increased at the same time. Male puberty did not affect PNNs, while female pubertal onset led to an abrupt decrease in the total number of PNNs that persisted through mid-adolescence before increasing at P60. Despite the change in PNN number, the intensity of female PNNs was not affected by puberty. Thus, though males and females show increases in mPFC PNNs during adolescence, the pubertal decrease in the number of PNNs in female rats may indicate a difference in the pattern of maximal plasticity between the sexes during adolescence.

The often-overlooked dorsal diencephalic conduction system (DDCS) is a highly conserved pathway linking the basal forebrain and the monoaminergic brainstem. It consists of three key structures; the stria medullaris, the habenula and the fasciculus retroflexus. The first component of the DDCS, the stria medullaris, is a discrete bilateral tract composed of fibers from the basal forebrain that terminate in the triangular eminence of the stalk of the pineal gland, known as the habenula. The habenula acts as a relay hub where incoming signals from the stria medullaris are processed and subsequently relayed to the midbrain and hindbrain monoaminergic nuclei through the fasciculus retroflexus. As a result of its wide-ranging connections, the DDCS has recently been implicated in a wide range of behaviors related to reward processing, aversion and motivation. As such, an understanding of the structure and connections of the DDCS may help illuminate the pathophysiology of neuropsychiatric disorders such as depression, addiction and pain. This is the first review of all three components of the DDCS, the stria medullaris, the habenula and the fasciculus retroflexus, with particular focus on their anatomy, function and development.

Mental health problems often emerge in adolescence and are associated with reduced gray matter thickness or volume in the prefrontal cortex (PFC) and limbic system and reduced fractional anisotropy (FA) and increased mean diffusivity (MD) of white matter linking these regions. However, few studies have investigated whether internalizing and externalizing behavior are associated with brain structure in children and adolescents without mental health disorders, which is important for understanding the progression of symptoms. 67 T1-weighted and diffusion tensor imaging datasets were obtained from 48 typically developing participants aged 6-16 years (37M/30F; 19 participants had two visits). Volume was calculated in the prefrontal and limbic structures, and diffusion parameters were assessed in limbic white matter. Linear mixed effects models were used to compute associations between brain structure and internalizing and externalizing behavior, assessed using the Behavioral Assessment System for Children (BASC-2) Parent Rating Scale. Internalizing behavior was positively associated with MD of the bilateral cingulum. Gender interactions were found in the cingulum, with stronger positive relationships between MD and internalizing behavior in females. Externalizing behavior was negatively associated with FA of the left cingulum, and the left uncinate fasciculus showed an age-behavior interaction. No relationships between behavior and brain volumes survived multiple comparison correction. These results show altered limbic white matter FA and MD related to sub-clinical internalizing and externalizing behavior and further our understanding of neurological markers that may underlie risk for future mental health disorders.

The frontal aslant tract (FAT) is a recently documented white matter tract that connects the inferior and superior frontal gyri with a tendency to be more pronounced in the left hemisphere. This tract has been found to play a role in language functions, particularly verbal fluency. However, it is not entirely clear to what extent FAT asymmetry is related to performance benefits in language-related tasks. In the present study, we aimed to fill this gap by examining the correlations between asymmetric micro- and macro-structural properties of the FAT and performance on verbal fluency and lexical decision tasks. The results showed no correlation between the FAT and verbal fluency; however, lexical decision was correlated with FAT laterality. Specifically, greater left lateralization in both micro- and macro-structural properties was related to faster lexical decision response times. The results were not due merely to motor or decision-making processes, as responses in a simple discrimination control task showed no correlation with laterality. These data are the first to suggest a role for the FAT in mediating processes underlying lexical decision.

Word learning plays a central role in language development and is a key predictor for later academic success. The underlying neural basis of successful word learning in children is still unknown. Here, we took advantage of the opportunity afforded by diffusion-weighted magnetic resonance imaging to investigate neural plasticity in the white matter of typically developing preschool children as they learn words. We demonstrate that after 3 weeks of word learning, children showed significantly larger increases of fractional anisotropy (FA) in the left precentral white matter compared to two control groups. Average training accuracy was correlated with FA change in the white matter underlying the left dorsal postcentral gyrus, with children who learned more slowly showing larger FA increases in this region. Moreover, we found that the status of white matter in the left middle temporal gyrus, assumed to support semantic processes, is predictive for early stages of word learning. Our findings provide the first evidence for white matter plasticity following word learning in preschool children. The present results on learning novel words in children point to a key involvement of the left fronto-parietal fiber connection, known to be implicated in top-down attention as well as working memory. While working memory and attention have been discussed to participate in word learning in children, our training study provides evidence that the neural structure supporting these cognitive processes plays a direct role in word learning.

In this study, we examined a large sample of 231 generally healthy older adults across 4 years with regard to several brain anatomical measures (volumes of total grey matter volume: GM, normal appearing white matter: NAWM, lateral ventricle: LV, and white matter hypointensities: WMH) and psychometric intelligence (verbal and non-verbal). The dataset comprised four measurement occasions (baseline, 1-, 2-, and 4-year follow-ups). With this longitudinal data set, we evaluated level-level, level-change, and change-change relationships between the anatomical and psychometric measures using latent growth curve models. Our analyses indicate that GM and NAWM decreased significantly over the course of 4 years with annual percent changes of - 0.73% and - 0.79%, respectively. WMH and LV volumes increase with annual percent changes of 7.3% and 4%, respectively. Verbal and nonverbal IQ measures remained stable in our sample. In addition, we uncovered evidence for level-level and -change associations between several of the brain anatomical measures. With regard to brain-IQ associations, we observed a positive level-level association for GM and NAWM, indicating that participants with larger brain volumes demonstrate higher IQ measures. No substantial evidence was identified for level- or change-change associations between any of the brain metrics and the IQ measures. Taken together, these results suggest that while healthy older adults demonstrated age-related neuroanatomical decline over a time span of 4 years, these degenerative changes are not necessarily linked to simultaneous cognitive deterioration.

Long-term motor training, such as dance or gymnastics, has been associated with increased diffusivity and reduced fiber coherence in regions including the corticospinal tract. Comparisons between different types of motor experts suggest that experience might result in specific structural changes related to the trained effectors (e.g., hands or feet). However, previous studies have not segregated the descending motor pathways from different body-part representations in motor cortex (M1). Further, most previous diffusion tensor imaging studies used whole-brain analyses based on a single tensor, which provide poor information about regions where multiple white matter (WM) tracts cross. Here, we used multi-tensor probabilistic tractography to investigate the specific components of the descending motor pathways in well-matched groups of dancers, musicians and controls. To this aim, we developed a procedure to identify the WM regions below the motor representations of the head, hand, trunk and leg that served as seeds for tractography. Dancers showed increased radial diffusivity (RD) in comparison with musicians, in descending motor pathways from all the regions, particularly in the right hemisphere, whereas musicians had increased fractional anisotropy (FA) in the hand and the trunk/arm motor tracts. Further, dancers showed larger volumes compared to both other groups. Finally, we found negative correlations between RD and FA with the age of start of dance or music training, respectively, and between RD and performance on a melody task, and positive correlations between RD and volume with performance on a whole-body dance task. These findings suggest that different types of training might have different effects on brain structure, likely because dancers must coordinate movements of the entire body, whereas musicians focus on fewer effectors.

Hand preference is a striking example of functional lateralization, with 90% of the population preferentially using their right hand. However, the search for brain structural correlates of this lateralization has produced inconsistent results. While large-scale neuroimaging studies using automated methods have largely failed to find local anatomical asymmetries associated with hand preference, other studies identifying specific motor regions have been able to find local morphological and functional differences. The present study looked at brain asymmetries in the brain's motor system using established cortical landmarks to identify the somatomotor hand region and extracted regional volumes of subcortical and cerebellar regions. Our results showed a strong left-right asymmetry in the cortical hand region, with weaker asymmetries appearing in the striatum and cerebellar white matter. Such asymmetries were much more pronounced in right-handers, whereas much weaker or absent lateralizing effects were observed in left-handed subjects. This study demonstrates the importance of local landmarks in studying individual anatomical differences. More generally, establishing structural correlates of hand preference is important, as this could further establish the origins of cerebral lateralization.

Background: In patients with MS, the effect of structural damage to the corticospinal tract (CST) has been separately evaluated in the brain and spinal cord (SC), even though a cumulative impact is suspected., Objective: To evaluate CST damages on both the cortex and cervical SC, and examine their relative associations with motor function, measured both clinically and by electrophysiology., Methods: We included 43 patients with early relapsing-remitting MS. Lesions were manually segmented on SC (axial T2*) and brain (3D FLAIR) scans. The CST was automatically segmented using an atlas (SC) or tractography (brain). Lesion volume fractions and diffusion parameters were calculated for SC, brain and CST. Central motor conduction time (CMCT) and triple stimulation technique amplitude ratio were measured for 42 upper limbs, from 22 patients., Results: Mean lesion volume fractions were 5.2% in the SC portion of the CST and 0.9% in the brain portion. We did not find a significant correlation between brain and SC lesion volume fraction (r = 0.06, p = 0.68). The pyramidal EDSS score and CMCT were both significantly correlated with the lesion fraction in the SC CST (r = 0.39, p = 0.01 and r = 0.33, p = 0.03), but not in the brain CST., Conclusion: Our results highlight the major contribution of SC lesions to CST damage and motor function abnormalities.

We previously proposed a bipartite 'dorsal-ventral' model of human arcuate fasciculus (AF) morphology. This model does not, however, account for the 'vertical,' temporo-parietal subdivision of the AF described in earlier dissection and tractographic studies. In an effort to address the absence of the vertical AF (VAF) within 'dorsal-ventral' nomenclature, we conducted a dedicated tractographic and white-matter dissection study of this tract and another short, vertical, posterior-hemispheric fascicle: the vertical occipital fasciculus (VOF). We conducted atlas-based, non-tensor, deterministic tractography in 30 single subjects from the Human Connectome Project database and verified our results using an average diffusion atlas compiled from 842 separate normal subjects. We also performed white-matter dissection in four post-mortem specimens. Our  tractography results demonstrate that the VAF is, in fact, a bipartite system connecting the ventral parietal and temporal regions, with variable connective, and no volumetric lateralization. The VOF is a non-lateralized, non-segmented system connecting lateral occipital areas with basal-temporal regions. Importantly, the VOF was spatially dissociated from the VAF. As the VAF demonstrates no overall connective or volumetric lateralization, we postulate its distinction from the AF system and propose its re-naming to the 'temporo-parietal aslant tract,' (TPAT), with unique dorsal and ventral subdivisions. Our tractography results were supported by diffusion atlas and white-matter dissection findings.

Microstructural properties of white matter pathways are associated with concurrent reading abilities in children. In this longitudinal study, we asked whether properties of white matter pathways at the onset of learning to read would be associated with reading abilities at older ages. Children (N = 37) with a wide range of reading abilities completed standardized measures of language and phonological awareness and diffusion MRI at age 6 years. Mean tract-fractional anisotropy (FA) was extracted from reading-related pathways. At age 8, the same children were re-assessed using a standardized reading measure. Using linear regressions, we examined the contribution of tract-FA at age 6 to reading outcome at age 8, beyond known demographic and pre-literacy predictors of reading. Tract-FA of the left arcuate, left and right superior longitudinal fasciculus (SLF), and left inferior cerebellar peduncle (ICP) made unique contributions to reading outcome after consideration of sex and family history of reading delays. Tract-FA of the left and right SLF and left ICP made unique contributions to reading outcome after the addition of pre-literacy skills. Thus, cerebellar and bilateral cortical pathways represented a network associated with subsequent reading abilities. Early white matter properties may be associated with other neuropsychological functions that predict reading or may influence reading development, independent of reading-related abilities. Tract FA at early stages of learning to read may serve as a biomarker of later reading abilities.

Connectivity between brain regions is integral to efficient complex cognitive processing, making the study of white matter pathways in clarifying the neural mechanisms of individual differences in arithmetic abilities critical. This white matter connectivity underlying arithmetic has only been investigated through classic diffusion tensor imaging, which, due to methodological limitations, might lead to an oversimplification of the underlying anatomy. More complex non-tensor models, such as spherical deconvolution, however, allow a much more fine-grained delineation of the underlying brain anatomy. Against this background, the current study is the first to use spherical deconvolution to investigate white matter tracts and their relation to individual differences in arithmetic fluency in typically developing children. Participants were 48 typically developing 9-10-year-olds, who were all in grade 4, and who underwent structural diffusion-weighted magnetic resonance imaging scanning. Theoretically relevant white matter tracts were manually delineated with a region of interest approach, after which the hindrance modulated orientational anisotropy (HMOA) index, which provides information on the structural integrity of the tract at hand, was derived for each tract. These HMOA indices were correlated with measures of arithmetic fluency, using frequentist and Bayesian approaches. Our results point towards an association between the HMOA of the right inferior longitudinal fasciculus and individual differences in arithmetic fluency. This might reflect the efficiency with which children process Arabic numerals. Other previously found associations between white matter and individual differences in arithmetic fluency were not observed.

In primates, proximal cortical areas are interconnected via within-cortex "intrinsic" pathway, whereas distant areas are connected via "extrinsic" white matter pathway. To date, such distinction has not been clearly done for small-brained mammals like rodents. In this study, we systematically analyzed the data of Allen Mouse Brain Connectivity Atlas to answer this question and found that the ipsilateral cortical connections in mice are almost exclusively contained within the gray matter, although we observed exceptions for projections from the retrosplenial area and the medial/orbital frontal areas. By analyzing axonal projections within the gray matter using Cortical Box method, which enabled us to investigate the layer patterns across different cortical areas, we obtained the following results. First, widespread axonal projections were observed in both upper and lower layers in the vicinity of injections, whereas highly specific "point-to-point" projections were observed toward remote areas. Second, such long-range projections were predominantly aligned in the anteromedial-posterolateral direction. Third, in the majority of these projections, the connecting axons traveled through layer 6. Finally, the projections from the primary and higher order areas to distant targets preferentially terminated in the middle and superficial layers, respectively, suggesting hierarchical connections similar to those of primates. Overall, our study demonstrated conspicuous differences in gray/white matter segregation of axonal projections between rodents and primates, despite certain similarities in the hierarchical cortical organization.

Temporal discounting, the tendency to select a smaller reward offered sooner over a larger reward offered at a later time, has been associated with a number of real-world decision-making outcomes important for health and wellbeing. Neurobiological mechanisms supporting temporal discounting have been explored among younger participants, and these have considered white matter integrity. However, the white matter correlates of temporal discounting in older adults are unclear. We hypothesized that greater temporal discounting would be associated with poorer white matter integrity measures, more specifically lower fractional anisotropy and higher trace, in older adults. Participants were 302 older persons without dementia (mean age = 81.38, mean years of education = 15.75, 75.5% female, mean MMSE = 28.29) from the Rush Memory and Aging Project, a community-based longitudinal study of aging. Temporal discounting was assessed using standard elicitation questions. White matter integrity was assessed with diffusion tensor imaging (DTI). Regression models were adjusted for the effects of age, sex, education, and white matter lesions. Secondary models further adjusted for global cognition. Results revealed significant associations between temporal discounting and white matter integrity measures (FA and trace) in bilateral frontal, frontostriatal, and temporal-parietal lobe white matter tracts, and results remained significant after further accounting for global cognition. These results suggest that temporal discounting is inversely associated with white matter integrity in old age and that this association is independent of global cognition.

The subcortical white matter (SWM) has been traditionally considered as a site for passive-neutral-information transfer through cerebral cortex association and projection fibers. Yet, the presence of subcortical neuronal and glial "interstitial" cells expressing immunolabelled neurotransmitters/neuromodulators and synaptic vesicular proteins, and recent immunohistochemical and electrophysiological observations on the rat visual cortex as well as interactive regulation of myelinating processes support the possibility that SWM nests subcortical, regionally variable, distributed neuronal-glial circuits, that could influence information transfer. Their hypothetical involvement in regulating the timing and signal transfer probability at the SWM axonal components ought to be considered and experimentally analysed. Thus, the "interstitial" neuronal cells-associated with local glial cells-traditionally considered to be vestigial and functionally inert under normal conditions, they may well turn to be critical in regulating information transfer at the SWM.

Attention is considered as one of the pre-requisites of conscious perception. Phasic alerting and exogenous orienting improve conscious perception of near-threshold information through segregated brain networks. Using a multimodal neuroimaging approach, combining data from functional MRI (fMRI) and diffusion-weighted imaging (DWI), we investigated the influence of white matter properties of the ventral branch of superior longitudinal fasciculus (SLF III) in functional interactions between attentional systems and conscious perception. Results revealed that (1) reduced integrity of the left hemisphere SLF III was predictive of the neural interactions observed between exogenous orienting and conscious perception, and (2) increased integrity of the left hemisphere SLF III was predictive of the neural interactions observed between phasic alerting and conscious perception. Our results combining fMRI and DWI data demonstrate that structural properties of the white matter organization determine attentional modulations over conscious perception.

Through learning and practice, we can acquire numerous skills, ranging from the simple (whistling) to the complex (memorizing operettas in a foreign language). It has been proposed that complex learning requires a network of brain regions that interact with one another via white matter pathways. One candidate white matter pathway, the uncinate fasciculus (UF), has exhibited mixed results for this hypothesis: some studies have shown UF involvement across a range of memory tasks, while other studies report null results. Here, we tested the hypothesis that the UF supports associative memory processes and that this tract can be parcellated into sub-tracts that support specific types of memory. Healthy young adults performed behavioral tasks (two face-name learning tasks, one word pair memory task) and underwent a diffusion-weighted imaging scan. Our results revealed that variation in UF microstructure was significantly associated with individual differences in performance on both face-name tasks, as well as the word association memory task. A UF sub-tract, functionally defined by its connectivity between face-selective regions in the anterior temporal lobe and orbitofrontal cortex, selectively predicted face-name learning. In contrast, connectivity between the fusiform face patch and both anterior face patches had no predictive validity. These findings suggest that there is a robust and replicable relationship between the UF and associative learning and memory. Moreover, this large white matter pathway can be subdivided to reveal discrete functional profiles.

Purpose: The aim of this study is to study the age, gender and lateral asymmetry-related white matter changes of long association tracts throughout late childhood and adolescence into adulthood using diffusion tensor tractography (DTT)., Methods: DTT was performed in 44 healthy subjects aged 7-45 years. Fractional anisotropy (FA), radial diffusivity (RD), axial diffusivity (AD), Trace, density and volume were calculated for long association tracts, namely the inferior fronto-occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF), uncinate fasciculus, superior longitudinal fasciculus (SLF) and its arcuate fibres. FA and diffusivity indices were correlated as function of age using Pearson correlation test. Comparison between males and females, and comparison between both hemispheres among all participants were also performed. A p value less than .01 was considered significant., Results: The majority of the examined tracts (SLF and IFOF of both hemispheres, and the arcuate fasciculus, uncinate fasciculus, and ILF of the left hemisphere) followed a common pattern of metric changes with age. This pattern was characterized by significant FA increase accompanied by reduction in RD, Trace without significant AD changes. The right arcuate fasciculus showed similar pattern but without significant FA changes. The right uncinate and right ILF fasciculus demonstrated significant reduction in RD, Trace and AD, with and without significant FA increase, respectively. Left hemispheric dominance regarding the FA and diffusivity indices was demonstrated in uncinate fasciculus with no significant gender-related differences., Conclusion: Significant microstructural tract-specific maturation processes continue throughout late childhood into adulthood. These processes may represent stages in a cascade of age-related maturation in white matter microstructure.

The neural foundations underlying semantic processing have been extensively investigated, highlighting a pivotal role of the ventral stream. However, although studies concerning the involvement of the left ventral route in verbal semantics are proficient, the potential implication of the right ventral pathway in non-verbal semantics has been to date unexplored. To gain insights on this matter, we used an intraoperative direct electrostimulation to map the structures mediating the non-verbal semantic system in the right hemisphere. Thirteen patients presenting with a right low-grade glioma located within or close to the ventral stream were included. During the 'awake' procedure, patients performed both a visual non-verbal semantic task and a verbal (control) task. At the cortical level, in the right hemisphere, we found non-verbal semantic-related sites (n = 7 in 6 patients) in structures commonly associated with verbal semantic processes in the left hemisphere, including the superior temporal gyrus, the pars triangularis, and the dorsolateral prefrontal cortex. At the subcortical level, we found non-verbal semantic-related sites in all but one patient (n = 15 sites in 12 patients). Importantly, all these responsive stimulation points were located on the spatial course of the right inferior fronto-occipital fasciculus (IFOF). These findings provide direct support for a critical role of the right IFOF in non-verbal semantic processing. Based upon these original data, and in connection with previous findings showing the involvement of the left IFOF in non-verbal semantic processing, we hypothesize the existence of a bilateral network underpinning the non-verbal semantic system, with a homotopic connectional architecture.

Human brain imaging revealed that the brain can undergo structural plasticity following new learning experiences. Most magnetic resonance imaging (MRI) uncovered morphometric alternation in cortical density after the long-term training of weeks to months. A recent diffusion tensor imaging (DTI) study has found changes in diffusion indices after 2 h of training, primarily in the hippocampus. However, whether a short learning experience can induce microstructural changes in the neocortex is still unclear. Here, we used diffusion MRI, a method sensitive to tissue microstructure, to study cortical plasticity. To attain cortical involvement, we used a short language task (under 1 h) of introducing new lexical items (flower names) to the lexicon. We have found significant changes in diffusivity in cortical regions involved in language and reading (inferior frontal gyrus, middle temporal gyrus, and inferior parietal lobule). In addition, the difference in the values of diffusivity correlated with the lexical learning rate in the task. Moreover, significant changes were found in white matter tracts near the cortex, and the extent of change correlated with behavioral measures of lexical learning rate. These findings provide first evidence of short-term cortical plasticity in the human brain after a short language learning task. It seems that short training of less than an hour of high cognitive demand can induce microstructural changes in the cortex, suggesting a rapid time scale of neuroplasticity and providing additional evidence of the power of MRI to investigate the temporal and spatial progressions of this process.

Computational analysis of communication efficiency of brain networks often relies on graph-theoretic measures based on the shortest paths between network nodes. Here, we explore a communication scheme that relaxes the assumption that information travels exclusively through optimally short paths. The scheme assumes that communication between a pair of brain regions may take place through a path ensemble comprising the k-shortest paths between those regions. To explore this approach, we map path ensembles in a set of anatomical brain networks derived from diffusion imaging and tractography. We show that while considering optimally short paths excludes a significant fraction of network connections from participating in communication, considering k-shortest path ensembles allows all connections in the network to contribute. Path ensembles enable us to assess the resilience of communication pathways between brain regions, by measuring the number of alternative, disjoint paths within the ensemble, and to compare generalized measures of path length and betweenness centrality to those that result when considering only the single shortest path between node pairs. Furthermore, we find a significant correlation, indicative of a trade-off, between communication efficiency and resilience of communication pathways in structural brain networks. Finally, we use k-shortest path ensembles to demonstrate hemispherical lateralization of efficiency and resilience.

What are the neurophysiological determinants of sustained supra-normal inhibitory control performance? We addressed this question by coupling multimodal neuroimaging and behavioral investigations of experts in fencing who underwent more than 20,000 h of inhibitory control training over 15 years. The superior control of the experts manifested behaviorally as a speeding-up of inhibition processes during a Go/NoGo task and was accompanied by changes in bilateral inferior frontal white matter microstructure. In the expert group, inhibition performance correlated positively with the fractional anisotropy (FA) of white matter tracts projecting to the basal ganglia, and the total training load with the FA in supplementary motor areas. Critically, the experts showed no changes in grey matter volume or in the functional organization of the fronto-basal inhibitory control network. The fencers' performance and neural activity during a 2-back working memory task did not differ from those of the controls, ensuring that their expertise was specific to inhibitory control. Our results indicate that while phasic changes in the patterns of neural activity and grey matter architecture accompany inhibitory control improvement after short- to medium- term training, long-lasting inhibitory control improvements primarily depend on the reinforcement of fronto-basal structural connectivity.

The evolutionary process of adaptation to an obligatory aquatic existence dramatically modified cetacean brain structure and function. The brain of the killer whale (Orcinus orca) may be the largest of all taxa supporting a panoply of cognitive, sensory, and sensorimotor abilities. Despite this, examination of the O. orca brain has been limited in scope resulting in significant deficits in knowledge concerning its structure and function. The present study aims to describe the neural organization and potential function of the O. orca brain while linking these traits to potential evolutionary drivers. Magnetic resonance imaging was used for volumetric analysis and three-dimensional reconstruction of an in situ postmortem O. orca brain. Measurements were determined for cortical gray and cerebral white matter, subcortical nuclei, cerebellar gray and white matter, corpus callosum, hippocampi, superior and inferior colliculi, and neuroendocrine structures. With cerebral volume comprising 81.51 % of the total brain volume, this O. orca brain is one of the most corticalized mammalian brains studied to date. O. orca and other delphinoid cetaceans exhibit isometric scaling of cerebral white matter with increasing brain size, a trait that violates an otherwise evolutionarily conserved cerebral scaling law. Using comparative neurobiology, it is argued that the divergent cerebral morphology of delphinoid cetaceans compared to other mammalian taxa may have evolved in response to the sensorimotor demands of the aquatic environment. Furthermore, selective pressures associated with the evolution of echolocation and unihemispheric sleep are implicated in substructure morphology and function. This neuroanatomical dataset, heretofore absent from the literature, provides important quantitative data to test hypotheses regarding brain structure, function, and evolution within Cetacea and across Mammalia.

Recent evidence suggests that individual differences in physical activity (PA) may be associated with individual differences in white matter microstructure and with grey matter volume of the hippocampus. Therefore, this study investigated the association between PA and white matter microstructure of pathways connecting to the hippocampus. A total of 33 young, healthy adults underwent magnetic resonance imaging (MRI). High angular resolution diffusion-weighted imaging and multi-component relaxometry MRI scans (multi-component driven equilibrium pulse observation of T1 and T2) were acquired for each participant. Activity levels (AL) of participants were calculated from 72-h actigraphy recordings. Tractography using the damped Richardson Lucy algorithm was used to reconstruct the fornix and bilateral parahippocampal cinguli (PHC). The mean fractional anisotropy (FA) and the myelin water fraction (MWF), a putative marker of myelination, were determined for each pathway. A positive correlation between both AL and FA and between AL and MWF were hypothesized for the three pathways. There was a selective positive correlation between AL and MWF in the right PHC (r = 0.482, p = 0.007). Thus, our results provide initial in vivo evidence for an association between myelination of the right PHC and PA in young healthy adults. Our results suggest that MWF may not only be more specific, but also more sensitive than FA to detect white matter microstructural alterations. If PA was to induce structural plasticity of the right PHC this may contribute to reverse structural alterations of the right PHC in neuropsychiatric disorder with hippocampal pathologies.

Understanding the genetic factors underlying brain structural connectivity is a major challenge in imaging genetics. Here, we present results from genome-wide association studies (GWASs) of whole-brain white matter (WM) fractional anisotropy (FA), an index of microstructural coherence measured using diffusion tensor imaging. Data from independent GWASs of 355 Swedish and 250 Norwegian healthy adults were integrated by meta-analysis to enhance power. Complementary GWASs on behavioral data reflecting processing speed, which is related to microstructural properties of WM pathways, were performed and integrated with WM FA results via multimodal analysis to identify shared genetic associations. One locus on chromosome 17 (rs145994492) showed genome-wide significant association with WM FA (meta P value = 1.87 × 10 -08 ). Suggestive associations (Meta P value <1 × 10 -06 ) were observed for 12 loci, including one containing ZFPM2 (lowest meta P value = 7.44 × 10 -08 ). This locus was also implicated in multimodal analysis of WM FA and processing speed (lowest Fisher P value = 8.56 × 10 -07 ). ZFPM2 is relevant in specification of corticothalamic neurons during brain development. Analysis of SNPs associated with processing speed revealed association with a locus that included SSPO (lowest meta P value = 4.37 × 10 -08 ), which has been linked to commissural axon growth. An intergenic SNP (rs183854424) 14 kb downstream of CSMD1, which is implicated in schizophrenia, showed suggestive evidence of association in the WM FA meta-analysis (meta P value = 1.43 × 10 -07 ) and the multimodal analysis (Fisher P value = 1 × 10 -07 ). These findings provide novel data on the genetics of WM pathways and processing speed, and highlight a role of ZFPM2 and CSMD1 in information processing in the brain.

The somatotopic organization of the primary motor cortex is well documented. However, a possible somatotopy of the network involved in motor control, i.e., eliciting negative motor phenomena during electrostimulation, is unknown in humans, particularly at the subcortical level. Here, we performed electrical stimulation mapping in awake patients operated for gliomas, to study the distribution of the white matter tracts subserving movement control of the lower limb, upper limb(s), and speech. Eighteen patients underwent awake surgery for frontal low-grade gliomas, by using intraoperative subcortical electrostimulation mapping to search interference with movement of the leg, arm(s), and face. We assessed the negative motor responses and their distribution throughout the tracts located under premotor areas. The corresponding stimulation sites were reported on a standard brain template for visual analysis and between-subjects comparisons. During stimulation of the white matter underneath the dorsal premotor cortex and supplementary motor area, rostral to the corticospinal tracts, all patients experienced cessation of the movement of lower and upper limbs, of bimanual coordination, and/or speech. These subcortical sites were somatotopically distributed. Indeed, stimulation of the fibers from mesial to lateral directions and from posterior to anterior directions evoked arrest of movement of the lower limb (mesially and posteriorly), upper limb(s), and face/speech (laterally and anteriorly). There were no postoperative permanent deficits. This is the first evidence of a somatotopic organization of the white matter bundles underpinning movement control in humans. A better knowledge of the distribution of this motor control network may be helpful in neurosciences and neurosurgery.

Phonetics experts are highly trained to analyze and transcribe speech, both with respect to faster changing, phonetic features, and to more slowly changing, prosodic features. Previously we reported that, compared to non-phoneticians, phoneticians had greater local brain volume in bilateral auditory cortices and the left pars opercularis of Broca's area, with training-related differences in the grey-matter volume of the left pars opercularis in the phoneticians group (Golestani et al. 2011). In the present study, we used diffusion MRI to examine white matter microstructure, indexed by fractional anisotropy, in (1) the long segment of arcuate fasciculus (AF&#95;long), which is a well-known language tract that connects Broca's area, including left pars opercularis, to the temporal cortex, and in (2) the fibers arising from the auditory cortices. Most of these auditory fibers belong to three validated language tracts, namely to the AF&#95;long, the posterior segment of the arcuate fasciculus and the middle longitudinal fasciculus. We found training-related differences in phoneticians in left AF&#95;long, as well as group differences relative to non-experts in the auditory fibers (including the auditory fibers belonging to the left AF&#95;long). Taken together, the results of both studies suggest that grey matter structural plasticity arising from phonetic transcription training in Broca's area is accompanied by changes to the white matter fibers connecting this very region to the temporal cortex. Our findings suggest expertise-related changes in white matter fibers connecting fronto-temporal functional hubs that are important for phonetic processing. Further studies can pursue this hypothesis by examining the dynamics of these expertise related grey and white matter changes as they arise during phonetic training.

The steepness of the delay discounting function shows considerable interindividual differences. Moreover, faster devaluation of future rewards has been consistently observed in pathological gamblers (PGs). Here, we asked whether variability in delay discounting is at least partially driven by differences in the anatomy of gray and white matter. For 40 healthy young subjects (study 1) as well as 15 PG and 15 age-matched healthy controls (HCs, study 2), the individual discounting parameter k was obtained. Based on 3D T1-weighted high-resolution magnetic resonance scans and diffusion tensor imaging, we performed voxel-based morphometry and tract-based spatial statistics, respectively, to examine the relation of gray matter volume (GMV) and white matter properties (as indicated by fractional anisotropy, FA) to k. Healthy groups from both studies showed a negative correlation between k and FA for the superior longitudinal fascicle and inferior longitudinal fascicle, whereas a positive correlation was found in the PG group for the inferior longitudinal fascicle and left inferior fronto-occipital fascicle. The latter also was significantly different between HC and PG in the group statistics (albeit on the right side), thus suggesting that this is a significant structure for the development of pathological gambling. GMV of the right frontal orbital cortex, left insular cortex and right lateral occipital cortex showed a positive correlation to k HC (studies 1 and 2) and PG, whereas a negative correlation was found for the left frontal pole in all three groups. Group comparison of GMV (study 2) revealed a decrease in PG for several cortical and subcortical areas.

The left hemisphere lateralization bias for language functions, such as syntactic processing and semantic retrieval, is well known. Although several theories and clinical data indicate a link between speech motor execution and language, the functional and structural brain lateralization for these functions has never been examined concomitantly in the same individuals. Here, we used functional MRI during rapid silent syllable repetition (/lalala/, /papapa/ and /pataka/, known as oral diadochokinesis or DDK) to map the cortical representation of the articulators in 17 healthy adults. In these same participants, functional lateralization for language production was assessed using the well-established verb generation task. We then used DDK-related fMRI activation clusters to guide tractography of the corticobulbar tract from diffusion-weighted MRI. Functional MRI revealed a wide inter-individual variability of hemispheric asymmetry patterns (left and right dominant, as well as bilateral) for DDK in the motor cortex, despite predominantly left hemisphere dominance for language-related activity in Broca's area. Tractography revealed no evidence for structural asymmetry (based on fractional anisotropy) within the corticobulbar tract. To our knowledge, this study is the first to reveal that motor brain activation for syllable repetition is unrelated to functional asymmetry for language production in adult humans. In addition, we found no evidence that the human corticobulbar tract is an asymmetric white matter pathway. We suggest that the predominance of dysarthria following left hemisphere infarct is probably a consequence of disrupted feedback or input from left hemisphere language and speech planning regions, rather than structural asymmetry of the corticobulbar tract itself.

Cognitive decline, especially the slowing of information processing speed, is associated with normal ageing. This decline may be due to brain cortico-cortical disconnection caused by age-related white matter deterioration. We present results from a large, narrow age range cohort of generally healthy, community-dwelling subjects in their seventies who also had their cognitive ability tested in youth (age 11 years). We investigate associations between older age brain white matter structure, several measures of information processing speed and childhood cognitive ability in 581 subjects. Analysis of diffusion tensor MRI data using Tract-based Spatial Statistics (TBSS) showed that all measures of information processing speed, as well as a general speed factor composed from these tests (g speed), were significantly associated with fractional anisotropy (FA) across the white matter skeleton rather than in specific tracts. Cognitive ability measured at age 11 years was not associated with older age white matter FA, except for the g speed-independent components of several individual processing speed tests. These results indicate that quicker and more efficient information processing requires global connectivity in older age, and that associations between white matter FA and information processing speed (both individual test scores and g speed), unlike some other aspects of later life brain structure, are generally not accounted for by cognitive ability measured in youth.

Plasticity of white matter tracts is thought to be essential for cognitive development and academic skill acquisition in children. However, a dearth of high-quality diffusion tensor imaging (DTI) data measuring longitudinal changes with learning, as well as methodological difficulties in multi-time point tract identification have limited our ability to investigate plasticity of specific white matter tracts. Here, we examine learning-related changes of white matter tracts innervating inferior parietal, prefrontal and temporal regions following an intense 2-month math tutoring program. DTI data were acquired from 18 third grade children, both before and after tutoring. A novel fiber tracking algorithm based on a White Matter Query Language (WMQL) was used to identify three sections of the superior longitudinal fasciculus (SLF) linking frontal and parietal (SLF-FP), parietal and temporal (SLF-PT) and frontal and temporal (SLF-FT) cortices, from which we created child-specific probabilistic maps. The SLF-FP, SLF-FT, and SLF-PT tracts identified with the WMQL method were highly reliable across the two time points and showed close correspondence to tracts previously described in adults. Notably, individual differences in behavioral gains after 2 months of tutoring were specifically correlated with plasticity in the left SLF-FT tract. Our results extend previous findings of individual differences in white matter integrity, and provide important new insights into white matter plasticity related to math learning in childhood. More generally, our quantitative approach will be useful for future studies examining longitudinal changes in white matter integrity associated with cognitive skill development.

Some of the known sex differences in white matter emerge during adolescence. Here, we replicate and extend our previous findings of sex differences in the structure of the corticospinal tract (Perrin et al. 2009; Hervé et al. 2009). In a large normative sample of adolescents, we observed age × sex interactions in the signal intensity of T1-weighted (T1W) images (n = 941) and in magnetization transfer ratio (MTR; n = 761); both features were inversely associated with age in males but not in females. Moreover, we hypothesized that the age-related differences in CST structure exhibited by males would be mediated by differences in puberty stage and levels of bioavailable testosterone. We confirmed this prediction using mediation analysis with bootstrapping. These findings suggest that sex differences in the CST structure observed during male adolescence may be due to multiple processes associated with puberty, including (but not limited to) the rising levels of testosterone.

Infancy and early childhood are periods of rapid brain development, during which brain structure and function mature alongside evolving cognitive ability. An important neurodevelopmental process during this postnatal period is the maturation of the myelinated white matter, which facilitates rapid communication across neural systems and networks. Though prior brain imaging studies in children (4 years of age and above), adolescents, and adults have consistently linked white matter development with cognitive maturation and intelligence, few studies have examined how these processes are related throughout early development (birth to 4 years of age). Here, we show that the profile of white matter myelination across the first 5 years of life is strongly and specifically related to cognitive ability. Using a longitudinal design, coupled with advanced magnetic resonance imaging, we demonstrate that children with above-average ability show differential trajectories of myelin development compared to average and below average ability children, even when controlling for socioeconomic status, gestation, and birth weight. Specifically, higher ability children exhibit slower but more prolonged early development, resulting in overall increased myelin measures by ~3 years of age. These results provide new insight into the early neuroanatomical correlates of cognitive ability, and suggest an early period of prolonged maturation with associated protracted white matter plasticity may result in strengthened neural networks that can better support later development. Further, these results reinforce the necessity of a longitudinal perspective in investigating typical or suspected atypical cognitive maturation.

The areas of academic interest (sciences or humanities) and area of study have been known to be associated with a number of factors associated with autistic traits. However, despite the vast amount of literature on the psychological and physiological characteristics associated with faculty membership, brain structural characteristics associated with faculty membership have never been investigated directly. In this study, we used voxel-based morphometry to investigate differences in regional gray matter volume (rGMV)/regional white matter volume (rWMV) between science and humanities students to test our hypotheses that brain structures previously robustly shown to be altered in autistic subjects are related to differences in faculty membership. We examined 312 science students (225 males and 87 females) and 179 humanities students (105 males and 74 females). Whole-brain analyses of covariance revealed that after controlling for age, sex, and total intracranial volume, the science students had significantly larger rGMV in an anatomical cluster around the medial prefrontal cortex and the frontopolar area, whereas the humanities students had significantly larger rWMV in an anatomical cluster mainly concentrated around the right hippocampus. These anatomical structures have been linked to autism in previous studies and may mediate cognitive functions that characterize differences in faculty membership. The present results may support the ideas that autistic traits and characteristics of the science students compared with the humanities students share certain characteristics from neuroimaging perspectives. This study improves our understanding of differences in faculty membership which is the link among cognition, biological factors, disorders, and education (academia).

To evaluate brain development longitudinally in premature infants without abnormalities as compared to healthy full-term newborns, we assessed fMRI brain activity patterns in response to linguistic stimuli and white matter structural development focusing on language-related fibres. A total sample of 29 preterm newborns and 26 at term control newborns underwent both fMRI and DTI. Griffiths test was performed at 6 months of corrected age to assess development. Auditory fMRI data were analysed in 17 preterm newborns at three time points [34, 41 and 44 weeks of post menstrual age (wPMA)] and in 15 controls, at term. Analysis showed a distinctive pattern of cortical activation in preterm newborns up to 29 wPMA moving from early prevalent left temporal and supramarginal area activation in the preterm period, to a bilateral temporal and frontoopercular activation in the at term equivalent period and to a more fine-grained left pattern of activity at 44 wPMA. At term controls showed instead greater bilateral posterior thalamic activation. The different pattern of brain activity associated to preterm newborns mirrors their white matter maturation delay in peripheral regions of the fibres and thalamo-cortical radiations in subcortical areas of both hemispheres, pointing to different transient thalamo-cortical development due to prematurity. Evidence for functional thalamic activation and more mature subcortical tracts, including thalamic radiations, may represent the substantial gap between preterm and at term infants. The transition between bilateral temporal activations at term age and leftward activations at 44 weeks of PMA is correlated to better neuropsychological results in Griffiths test.

White matter tracts are important for the trafficking of neural progenitor cells (NPCs) in both normal and pathological conditions, but the underlying mechanism is not clear. The directionality of white matter is advantageous for molecules or cells to distribute over a long distance, but this feature is unlikely solely responsible for efficient migration. The present study hypothesizes that the efficient migration of NPCs into white matter is under the influences of neurochemical attraction—CXCL12/CXCR4 signaling, a major mechanism underlying the targeted migration of NPCs. To test this view, the present study investigated the effects of CXCL12 administration into the corpus callosum (CC) on the migratory behavior of transplanted NPCs. A living animal tracking platform based on MRI and a magnetic cell labeling technique was employed. The NPCs were magnetically labeled and then transplanted at the right end of the CC. CXCL12 was infused continuously at the left end. Migration of NPCs was monitored repeatedly over a 7-day course using 3D gradient echo T2*-weighted imaging. It was found that, CXCL12 induced NPCs to migrate up to 1,881 μm from the graft whereas the spontaneous migration was mere 200 μm. CXCL12 induced migration that was nine times as efficient in the speed. The results indicate that the CXCL12/CXCR4 signaling may be a mechanism via which NPCs efficiently migrate along the white matter tracts. The study also presents a potential strategy for facilitating the targeted migration in NPC therapy for brain disorders.

Many previous studies suggested that both short-term and long-term motor training can modulate brain structures. However, little evidence exists for such brain anatomical changes in top-level gymnasts. Using diffusion-weighted and structural magnetic resonance images of the human brain, we applied voxel-based morphometry (VBM) and tract-based spatial statistics (TBSS) as well as FA-VBA (voxel-based analysis of fractional anisotropy, a VBM-style analysis) methods to quantitatively compare the brain structural differences between the world class gymnasts (WCG) and the non-athlete groups. In order to reduce the rate of false positive findings, we first determined that the clusters defined at a threshold of t > 2.3 and a cluster significance of p < 0.05 (FWE-corrected) across all subjects were the brain regions that showed significant differences in a between-group comparison. We then constructed several between-group comparisons based on the repeated diffusion or structural MRI data and created the intersecting regions from multiple between-group comparisons. Thus, we found significantly decreased fractional anisotropy (FA) not only in the white matter of the WCG in areas that included the bilateral superior longitudinal fasciculus, inferior longitudinal fasciculus, and inferior occipito-frontal fascicle, but also in the gray matter of the WCG in areas that included the bilateral middle cingulum, bilateral postcentral gyri, and bilateral motor regions. We also identified significantly increased gray matter density in the WCG, especially in the left inferior frontal gyrus, bilateral inferior and superior parietal lobule, bilateral superior lateral occipital cortex, left cuneus, left angular gyrus, and right postcentral gyrus. We speculate that the brain changes of the WCG may reflect the gymnasts' extraordinary ability to estimate the direction of their movements, their speed of execution, and their identification of their own and surrounding objects' locations. Our findings suggest that our method of constructing intersecting regions from multiple between-group comparison can considerably reduce the false positives, and our results provide new insights into the brain structure changes induced by long-term intensive gymnastic training.

Introduction: Language lateralization is unique to humans. Functional MRI (fMRI) and diffusion tensor imaging (DTI) enable the study of language areas and white matter fibers involved in language, respectively. The objective of this study was to correlate arcuate fasciculus (AF) laterality by diffusion tensor imaging with that by fMRI in preadolescent children which has not yet been reported., Methods: Ten children between 8 and 12 years were subjected to fMRI and DTI imaging using Siemens 1.5 T MRI. Two language fMRI paradigms--visual verb generation and word pair task--were used. Analysis was done using SPM8 software. In DTI, the fiber volume of the arcuate fasciculus (AFV) and fractional anisotropy (FA) was measured. The fMRI Laterality Index (fMRI-LI) and DTI Laterality Index (DTI-LI) were calculated and their correlation assessed using the Pearson Correlation Index., Results: Of ten children, mean age 10.6 years, eight showed left lateralization while bilateral language lateralization was seen in two. AFV by DTI was more on the left side in seven of the eight children who had left lateralization by fMRI. DTI could not trace the AF in one child. Of the two with bilateral language lateralization on fMRI, one showed larger AFV on the right side while the other did not show any asymmetry. There was a significant correlation (p < 0.02) between fMRI-LI and DTI-LI. Group mean of AFV by DTI was higher on the left side (2659.89 ± 654.75 mm(3)) as compared to the right (1824.11 ± 582.81 mm(3)) (p < 0.01)., Conclusion: Like fMRI, DTI also reveals language laterality in children with a high degree of correlation between the two imaging modalities.

Selective attention to features of interest facilitates object processing in a cluttered and dynamic environment. Previous research found that distinct networks of regions across cortex are activated depending on the attended feature. These networks typically consist of posterior feature-preferring regions and anterior regions involved in attentional processes. In the current study, we investigated the role of white matter connections between the posterior and anterior regions within these networks for attention to features of novel colored dynamic objects. We asked participants to perform a 1-back feature-attention task while we acquired both functional and diffusion-weighted images. Using tract-based spatial statistics and probabilistic tractography, we found that the right superior longitudinal fasciculus (SLF) connected posterior and anterior object-processing regions and that voxels within the SLF correlated with response times on the task. Posterior and anterior regions that were anatomically connected also had increased functional connectivity relative to posterior and anterior regions that were not connected. Our results demonstrate that both functional and structural information has to be taken into account to understand selective attention and object perception.

Introduction: The ability of functional magnetic resonance imaging (fMRI) to detect activation in brain white matter (WM) is controversial. In particular, studies on the functional activation of WM tracts in the central auditory system are scarce. We utilized fMRI to assess and characterize the entire auditory WM pathway under robust experimental conditions involving the acquisition of a large number of functional volumes, the application of broadband auditory stimuli of high intensity, and the use of sparse temporal sampling to avoid scanner noise effects and increase signal-to-noise ratio., Methods: Nineteen healthy volunteers were subjected to broadband white noise in a block paradigm; each run had four sound-on/off alternations and was repeated nine times for each subject. Sparse sampling (TR=8 s) was used., Results: In addition to traditional gray matter (GM) auditory center activation, WM activation was detected in the isthmus and midbody of the corpus callosum (CC), tapetum, auditory radiation, lateral lemniscus, and decussation of the superior cerebellar peduncles. At the individual level, 13 of 19 subjects (68 %) had CC activation. Callosal WM exhibited a temporal delay of approximately 8 s in response to the stimulation compared with GM., Conclusions: These findings suggest that direct evaluation of the entire functional network of the central auditory system may be possible using fMRI, which may aid in understanding the neurophysiological basis of the central auditory system and in developing treatment strategies for various central auditory disorders.