Projection Fibers Research Articles

Tractography at 3T MRI of Corpus Callosum Tracts Crossing White Matter Hyperintensities.

The impact of white matter hyperintensities on the diffusion characteristics of crossing tracts is unclear. This study used quantitative tractography at 3T MR imaging to compare, in the same individuals, the diffusion characteristics of corpus callosum tracts that crossed white matter hyperintensities with the diffusion characteristics of corpus callosum tracts that did not pass through white matter hyperintensities. Brain T2 fluid-attenuated inversion recovery-weighted and diffusion tensor 3T MR imaging scans were acquired in 24 individuals with white matter hyperintensities. Tractography data were generated by the Fiber Assignment by Continuous Tracking method. White matter hyperintensities and corpus callosum tracts were manually segmented. In the corpus callosum, the fractional anisotropy, radial diffusivity, and mean diffusivity of tracts crossing white matter hyperintensities were compared with the fractional anisotropy, radial diffusivity, and mean diffusivity of tracts that did not cross white matter hyperintensities. The cingulum, long association fibers, corticospinal/bulbar tracts, and thalamic projection fibers were included for comparison. Within the corpus callosum, tracts that crossed white matter hyperintensities had decreased fractional anisotropy compared with tracts that did not pass through white matter hyperintensities (P = .002). Within the cingulum, tracts that crossed white matter hyperintensities had increased radial diffusivity compared with tracts that did not pass through white matter hyperintensities (P = .001). In the corpus callosum and cingulum, tracts had worse diffusion characteristics when they crossed white matter hyperintensities. These results support a role for white matter hyperintensities in the disruption of crossing tracts.

Basal ganglia and cerebellar interconnectivity within the human thalamus

Basal ganglia and the cerebellum are part of a densely interconnected network. While both subcortical structures process information in basically segregated loops that primarily interact in the neocortex, direct subcortical interaction has been recently confirmed by neuroanatomical studies using viral transneuronal tracers in non-human primate brains. The thalamus is thought to be the main relay station of both projection systems. Yet, our understanding of subcortical basal ganglia and cerebellar interconnectivity within the human thalamus is rather sparse, primarily due to limitation in the acquisition of in vivo tracing. Consequently, we strive to characterize projections of both systems and their potential overlap within the human thalamus by diffusion MRI and tractography. Our analysis revealed a decreasing anterior-to-posterior gradient for pallido-thalamic connections in: (1) the ventral-anterior thalamus, (2) the intralaminar nuclei, and (3) midline regions. Conversely, we found a decreasing posterior-to-anterior gradient for dentato-thalamic projections predominantly in: (1) the ventral-lateral and posterior nucleus; (2) dorsal parts of the intralaminar nuclei and the subparafascicular nucleus, and (3) the medioventral and lateral mediodorsal nucleus. A considerable overlap of connectivity pattern was apparent in intralaminar nuclei and midline regions. Notably, pallidal and cerebellar projections were both hemispherically lateralized to the left thalamus. While strikingly consistent with findings from transneuronal studies in non-human primates as well as with pre-existing anatomical studies on developmentally expressed markers or pathological human brains, our assessment provides distinctive connectional fingerprints that illustrate the anatomical substrate of integrated functional networks between basal ganglia and the cerebellum. Thereby, our findings furnish useful implications for cerebellar contributions to the clinical symptomatology of movement disorders.

Diffusion Tensor Imaging without Complex Statistical Analysis Could Be Helpful for Diagnosis

Objective: Thanks to fast developing technology, visualization of fiber tracts at brain is possible. But with the new developments, data processing and interpretation are becoming more difficult. Actually interpretations in these fields are mostly in-group analysis and are generally not useful on the basis of individual patient evaluations. In these regards, we investigated our cases with diffusion tensor imaging (DTI) and tried to show if the data could be interpreted simply by radiologist’s eye or not. Material: Our study consisted of 31 cases that were evaluated in our center with 3 Tesla Magnetic Resonance Imaging (MRI) units. Cranial DTI studies performed for ischemia, posttraumatic axonal injury, congenital malformation, neoplasia, autism, mental retardation and epilepsy. Cranial DTI was performed to demonstrate effected fiber tracts in neoplasia and ischemia cases and was applied to identify any gross anomaly in microstructural anatomy beside normal conventional MRI in other cases. DTI images were evaluated, along with fused conventional T1 weighted 3D high-resolution images and FA maps. DTI were performed at the first administration of the patients. Results: In addition to chronic ischemic focuses in patients with ischemia, DTI-FA images showed us relevant signal changes secondary to Wallerian degeneration in two cases. In traumatic brain injury cases, though being isointense on conventional sequences, FA values showed decreased values at the levels of the axonal discontinuity. Major abnormalities of association and projection fibers in congenital malformation cases were visualized at both 3D-DTI fused images and FA map images. Displacement, infiltration, destruction fibers were clearly visualized in neoplasia cases. However, any objective abnormality wasn’t reported at any cases diagnosed with motor mental retardation, epilepsy or neuropsychiatric diseases. Conclusion: Colored DTI images and FA maps are helpful in the way of diagnosis in most cases with organic pathologies; it is possible to obtain diagnostic information by vivacious images.

Peptidergic modulation of cerebellar nuclear neurons in promoting motor coordination

Event Abstract Back to Event Peptidergic modulation of cerebellar nuclear neurons in promoting motor coordination Jing-Ning Zhu1* and Jian-Jun Wang1* 1 Nanjing University, State Key Laboratory of Pharmaceutical Biotechnology and Department of Biological Science and Technology, School of Life Sciences, China The cerebellar circuitry receives not only classic glutamatergic mossy fibers and climbing fibers but also fibers containing various peptides, such as orexin and corticotropin-releasing factor (CRF). Both the orexinergic afferent inputs from the hypothalamus and the CRFergic climbing fiber-like afferent inputs from the inferior olive directly excite projection neurons rather than interneurons in the cerebellar interposed nucleus (IN), one of the final outputs of the spinocerebellum. In addition, orexin receptors and CRF receptors are selectively expressed on projection neurons in the IN. Na+-Ca2+ exchangers and inward rectifier K+ channels co-mediate the orexin-induced inward currents on IN projection neurons, whereas HCN channels and inward rectifier K+ channels contribute to the excitation induced by CRF. Furthermore, microinjection of orexin or CRF into bilateral cerebellar INs significantly promotes motor balance and coordination. Intriguingly, blocking orexinergic afferent inputs in IN does not influence routine movements but remarkably attenuates motor performances during motor challenges, whereas interfering CRFergic climbing fiber-like inputs directly leads to an ataxia-like motor incoordination. Therefore, through direct modulations on cerebellar nuclear projection neurons, peptidergic inputs may play important roles in the cerebellar circuitry, and actively promote cerebellar motor control. Acknowledgements Supported by NSFC grants 31330033, 91332124, 31471112, 31461163001, and SRFDP/RGC ERG grant 20130091140003. Keywords: Cerebellar circuitry, Cerebellar nucleus, CRF, orexin, motor control Conference: 14th Meeting of the Asian-Pacific Society for Neurochemistry, Kuala Lumpur, Malaysia, 27 Aug - 30 Aug, 2016. Presentation Type: Symposium 1: Motor Control and Sensorimotor Integration: Circuitry and Plasticity Topic: 14th Meeting of the Asian-Pacific Society for Neurochemistry Citation: Zhu J and Wang J (2016). Peptidergic modulation of cerebellar nuclear neurons in promoting motor coordination. Conference Abstract: 14th Meeting of the Asian-Pacific Society for Neurochemistry. doi: 10.3389/conf.fncel.2016.36.00005 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 26 Jul 2016; Published Online: 11 Aug 2016. * Correspondence: Prof. Jing-Ning Zhu, Nanjing University, State Key Laboratory of Pharmaceutical Biotechnology and Department of Biological Science and Technology, School of Life Sciences, Nanjing, Jiangsu, China, jnzhu@nju.edu.cn Prof. Jian-Jun Wang, Nanjing University, State Key Laboratory of Pharmaceutical Biotechnology and Department of Biological Science and Technology, School of Life Sciences, Nanjing, Jiangsu, China, jjwang@nju.edu.cn Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Jing-Ning Zhu Jian-Jun Wang Google Jing-Ning Zhu Jian-Jun Wang Google Scholar Jing-Ning Zhu Jian-Jun Wang PubMed Jing-Ning Zhu Jian-Jun Wang Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Secondary parkinsonism induced by hydrocephalus after subarachnoid and intraventricular hemorrhage.

Hydrocephalus can induce secondary parkinsonism (Shahar et al., 1988; Aggarwal et al., 1997; Racette et al., 2004). Physical factors such as increased ventricular pressure near the upper midbrain and basal ganglia are thought to cause mechanical disruption of dopaminergic systems (i.e., the nigrostriatal pathways from the medial substantia nigra to the caudate nuclei and putamen and its frontal projection fibers from the basal ganglia) (Asamoto et al., 1998; Yomo et al., 2006). Symptoms of parkinsonism are bradykinesia with rigidity, resting tremor, or postural instability, which can deteriorate a patient's physical function and functional recovery (Racette et al., 2004). Parkinsonian symptoms can be controlled by dopaminergic medication, meaning that the accurate diagnosis of secondary parkinsonism is important for proper management of stroke patients (Shahar et al., 1988; Aggarwal et al., 1997; Racette et al., 2004). Previous studies have investigated dopaminergic system dysfunction induced by hydrocephalus using single photon emission computed tomography (SPECT) and position emission tomography (PET) scanning (Shahar et al., 1988; Aggarwal et al., 1997; Racette et al., 2004; Nakayama et al., 2007). However, these methods are limited in their ability to clearly present the dopaminergic system.

Correlating quantitative tractography at 3T MRI and cognitive tests in healthy older adults.

This study used diffusion tensor imaging tractography at 3T MRI to relate cognitive function to white matter tracts in the brain. Brain T2 fluid attenuated inversion recovery-weighted and diffusion tensor 3T MRI scans were acquired in thirty-three healthy participants without mild cognitive impairment or dementia. They completed a battery of neuropsychological tests including the Montreal Cognitive Assessment, Stroop test, Trail Making Test B, Wechsler Memory Scale-III Longest span forward, Wechsler Memory Scale-III Longest span backward, Mattis Dementia Rating Scale, California Verbal Learning Test Version II Long Delay Free Recall,and Letter Number Sequencing. Tractography was generated by the Fiber Assignment by Continuous Tracking method. The corpus callosum, cingulum, long association fibers, corticospinal/bulbar tracts, thalamic projection fibers, superior cerebellar peduncle, middle cerebellar peduncle and inferior cerebellar peduncle were manually segmented. The fractional anisotropy (FA) and mean diffusivity (MD) of these tracts were quantified. We studied the association between cognitive test scores and the MD and FA of tracts while controlling for age and total white matter hyperintensities volume. Worse scores on the Stroop test was associated with decreased FA of the corpus callosum, corticospinal/bulbar tract, and thalamic projection tracts. Scores on the other cognitive tests were not associated with either the FA or MD of measured tracts. In healthy persons the Stroop test appears to be a better predictor of the microstructural integrity of white matter tracts measured by DTI tractography than other cognitive tests.

Analysis of the Conduction of Information and Its Integration in the Projection Systems Connecting the Basal Ganglia and the Rostromedial Tegmental Nucleus of the Dog Brain

Analysis of retrograde axonal transport studies of the projections between individual parts of the rostral and caudal sectors of the rostromedial tegmental nucleus (RMTg) and functionally diverse segments of striatal and pallidal structures was used to study the structural basis of information processing in the morphofunctional system of the basal ganglia. Topical elements were seen in the organization of the projections between these structures in the dog brain, suggesting the possibility of segregated conduction of information between the limbic segments of the RMTg and the limbic areas of the striopallidum. However, most striopallidal structures showed convergence of projection fibers running from neurons in functionally diverse parts of the RMTg, which may be evidence that functionally diverse information is integrated within these structures. Labeled sparsely branching, long-axon, “reticular” neurons of the RMTg projecting to striopallidal structures also provided evidence of the integrative function of the nucleus of interest. We evaluate data on the possible pathways conducting specific motor and limbic information and its integration in the structures of this system and the possibility of using them to create new models promoting our understanding of the functioning of the basal ganglia in health and disease.

P3Neural circuits for pain modulation in the central nervous system

Pain is a common and severe disease that affects millions of people worldwide and is difficult to treat. The main reason is that the mechanisms for pain information transmission and modulation have still not revealed. In the central nervous system (CNS), there are many long and short neural circuits constituted by axonal processes and are necessary for pain sensation. But the structures and functions of these pathways, especially those constituted by local axons and their collaterals are not known, which is essential for us to uncover the neural mechanisms of pain [1]. In our recent studies, the neural circuits involved in pain sensation in the CNS have been investigated with different methods, especially under the electron microscopic level [2]. The main results are as follows: (1) In the superficial laminae (lamina I and lamina II) of the spinal dorsal horn (SDH), substance P-immunoreactive (SP-ir) and calcitonin gene-related peptide (CGRP)-ir primary afferent terminals have been observed to make synapses with GABA- and glycine-ir neurons which could be activated by periphery painful stimulation, suggesting that the noxious information might be regulated by inhibitory interneurons in the SDH. (2) Endomorphin (EM) is a new member of the endogenous opioid family and specific ligand for μ-opioid receptor (MOR) [3]. Within the superficial laminae of the SDH, either EM-ir fibers from the primary afferents (Figure 1) or serotonin (5-HT)-ir fibers from the descending fibers of the brainstem raphe nuclei have been encountered to terminate onto the same neurons which send projection fibers to the parabrachial nucleus (PBN) or ventrolateral complex of the thalamus, indicating that the SDH might be a very special site for pain modulation. (3) Neurons in layer V of the anterior cingulate cortex (ACC) innervated by direct ascending fibers from the spinal dorsal horn, and then in turn, projected directly to the SDH. The excitation of these ACC-SDH projection neurons by nociceptive inputs could facilitate the activity of the nociceptive neurons in lamina I of the SDH, suggesting that the descending projection from ACC to SDH might directly potentiate the noxious information transmission. This effect might affect the patient and make them to feel much more painful [4]. (4) In the periaqueductal gray, EM released from the terminals originated from the EM-containing neurons in the hypothalamus binds to MOR expressing GABAeregic inhibitory interneurons and then results in disinhibition of 5-HTergic projection neurons, and finally to exert analgesic effects at the spinal cord level [5]. These results have provided morphological and functional evidence for the mechanisms underlying pain information transmission and modulation in the CNS.

Differential aging of cerebral white matter in middle-aged and older adults: A seven-year follow-up

The few extant reports of longitudinal white matter (WM) changes in healthy aging, using diffusion tensor imaging (DTI), reveal substantial differences in change across brain regions and DTI indices. According to the “last-in-first-out” hypothesis of brain aging late-developing WM tracts may be particularly vulnerable to advanced age. To test this hypothesis we compared age-related changes in association, commissural and projection WM fiber regions using a skeletonized, region of interest DTI approach. Using linear mixed effect models, we evaluated the influences of age and vascular risk at baseline on seven-year changes in three indices of WM integrity and organization (axial diffusivity, AD, radial diffusivity, RD, and fractional anisotropy, FA) in healthy middle-aged and older adults (mean age=65.4, SD=9.0years). Association fibers showed the most pronounced declines over time. Advanced age was associated with greater longitudinal changes in RD and FA, independent of fiber type. Furthermore, older age was associated with longitudinal RD increases in late-developing, but not early-developing projection fibers. These findings demonstrate the increased vulnerability of later developing WM regions and support the “last-in-first-out” hypothesis of brain aging.

Organization of the Pallidal Projections of the Rostromedial Tegmental Nucleus of the Dog Brain

The organization of the projections of the rostromedial tegmental nucleus (RMTN) to functionally diverse nuclei of the pallidum in the dog brain (n = 13) was studied by retrograde and anterograde transport of horseradish peroxidase. These studies showed that fibers formed by neurons in the limbic medial segments of the rostral and caudal divisions of the RMTN are directed to the limbic parts of the pallidum – the ventral zone of the globus pallidus and the ventral pallidum. Reciprocal connections were observed between the ventral pallidum and the medial part of the rostral RMTN. These data identify the potential for segregated conduction of limbic information via these projection systems. However, most pallidal structures showed convergence of projection fibers arising from neurons in functionally diverse parts of the RMTN. Thus, projection fibers from neurons in the motor lateral and limbic medial parts of the RMTN are directed to the limbic ventral segment of the globus pallidus and the entopeduncular nucleus, which are innervated by fibers formed by neurons in functionally diverse structures. The possible pathways for the conduction of functionally different information and its integration in the projection systems studied here are discussed.

White Matter Abnormalities in Autism and Unaffected Siblings.

This study was conducted to identify a potential neuroendophenotype for autism using diffusion tensor imaging. Whole-brain, voxel-based analysis of fractional anisotropy was conducted in 50 children: 19 with autism, 20 unaffected siblings, and 11 controls. Relative to controls, participants with autism exhibited bilateral reductions in fractional anisotropy across association, commissure, and projection fibers. The most severely affected tracts included the uncinate fasciculus, forceps minor, and inferior fronto-occipital fasciculus. Unaffected siblings also exhibited reductions in fractional anisotropy, albeit less severe with fewer affected tracts, sparing the uncinate fasciculus and forceps minor. These results suggest the presence of a neuroendophenotype for autism.

Comparative Study of the Major White Matter Tracts Anatomy in Equine, Feline and Canine Brains by Use of the Fibre Dissection Technique

The spatial anatomy of the white matter tracts is a subject of growing interest not only for researchers but also for clinicians. Imagistic methods have some limitations so that they should be confronted with dissection studies. The aim of this paper was to provide a three-dimensional view of the major white matter tracts in equine, feline and canine brains by use of the fibre dissection technique. Twenty cerebral hemispheres (six equine, four feline and 10 canine brains) were prepared according to the Klingler method. Stepwise mediolateral and lateromedial blunt dissections were performed using wooden sticks and spatulas. The lateromedial dissection was followed by the opening of the lateral ventricle. The use of the same multi-stage procedures resulted in a comparable exposure of the major association, projection and commissural fibres and their spatial relation with the lateral ventricle. To conclude, the proposed techniques are reproducible in equine, feline and canine brains and they can be successfully used for teaching, training or research in the field of neurobiology.

Abstract P157: Tractography of White Matter Connections Predicts for Vascular Cognitive Impairment in Hypertensive Patients

Vascular cognitive impairment (VCI) results by several vascular risk factors and, particularly, hypertension (HTN). The identification of early changes associated with later development of dementia is demanding. Great part of research has primarily focused on brain changes occuring in grey matter. However, more recent data highlighted that HTN may determine cognitive decline, even before manifest neurodegeneration. Diffusion tensor imaging (DTI) on magnetic resonance, opened the possibility to predict white matter connections that correlate with specific cognitive functions. In this study, we used DTI and cognitive assessment (CA), in order to identify a regional pattern of fractional anisotropy (FA) changes that could predict for VCI in hypertensive patients (HT). We have examined 15 HT (moderate to severe, with antihypertensive medications) vs 15 normotensive (NT), subjecting them to DTI and CA. HT had significant higher SBP (138±4 vs 118±3 in NT) and DBP (87±2 vs 75±2 in NT) (p<0.001), displayed a significant LV hypertrophic remodeling (LVM/BSA 112±5 vs 83±3 for NT) (p<0.0001), with a significant moderate increase in albuminuria (15.7±2.6 mg/24h vs 8.8±1.6 for NT) (p<0.03). When subjected to CA, HT had significantly worsen performance on both MoCA (22.66±0.97 vs 26.21±0.57 NT) and Stroop Test (34.50±3.87 vs 17.75±2.57 NT) (p<0.01). Conversely, tests regarding Verbal Fluency and Instrumental Activities of Daily Living revealed normal performance of HT, thus indicating a selective impairment of memory. Brain imaging showed that, while none of the patients had abnormal signal intensity on T1/T2-weighted MRI, DTI indices FA were significantly reduced in HT as vs NT. In particular, HT had lower FA in projection fibers related to impairment for non-verbal materials (Anterior Thalamic Radiation: 0.358±0.012 vs 0.330±0.006, p<0.05), association fibers involved in executive functioning and emotional regulation (Superior Longitudinal Fasciculus: 0.388±0.013 vs 0.356±0.007, p<0.05), limbic system fibers involved in attention tasks (cingulate gyrus: 0.364±0.009 vs 0.328±0.010, p<0.01). Our data highlight a novel paradigm of combined DTI/CA of HT patients, capable to identify, with great sensitivity, predictive signs of HTN-induced VCI.

Extensive White Matter Alterations and Its Correlations with Ataxia Severity in SCA 2 Patients.

BackgroundPrevious studies of SCA2 have revealed significant degeneration of white matter tracts in cerebellar and cerebral regions. The motor deficit in these patients may be attributable to the degradation of projection fibers associated with the underlying neurodegenerative process. However, this relationship remains unclear. Statistical analysis of diffusion tensor imaging enables an unbiased whole-brain quantitative comparison of the diffusion proprieties of white matter tracts in vivo.MethodsFourteen genetically confirmed SCA2 patients and aged-matched healthy controls participated in the study. Tract-based spatial statistics were performed to analyze structural white matter damage using two different measurements: fractional anisotropy (FA) and mean diffusivity (MD). Significant diffusion differences were correlated with the patient's ataxia impairment.ResultsOur analysis revealed decreased FA mainly in the inferior/middle/superior cerebellar peduncles, the bilateral posterior limb of the internal capsule and the bilateral superior corona radiata. Increases in MD were found mainly in cerebellar white matter, medial lemniscus, and middle cerebellar peduncle, among other regions. Clinical impairment measured with the SARA score correlated with FA in superior parietal white matter and bilateral anterior corona radiata. Correlations with MD were found in cerebellar white matter and the middle cerebellar peduncle.ConclusionOur findings show significant correlations between diffusion measurements in key areas affected in SCA2 and measures of motor impairment, suggesting a disruption of information flow between motor and sensory-integration areas. These findings result in a more comprehensive view of the clinical impact of the white matter degeneration in SCA2.

Interactive effects of physical activity and APOE-ε4 on white matter tract diffusivity in healthy elders

Older adult apolipoprotein-E epsilon 4 (APOE-ε4) allele carriers vary considerably in the expression of clinical symptoms of Alzheimer's disease (AD), suggesting that lifestyle or other factors may offer protection from AD-related neurodegeneration. We recently reported that physically active APOE-ε4 allele carriers exhibit a stable cognitive trajectory and protection from hippocampal atrophy over 18months compared to sedentary ε4 allele carriers. The aim of this study was to examine the interactions between genetic risk for AD and physical activity (PA) on white matter (WM) tract integrity, using diffusion tensor imaging (DTI) MRI, in this cohort of healthy older adults (ages of 65 to 89). Four groups were compared based on the presence or absence of an APOE-ε4 allele (High Risk; Low Risk) and self-reported frequency and intensity of leisure time physical activity (PA) (High PA; Low PA). As predicted, greater levels of PA were associated with greater fractional anisotropy (FA) and lower radial diffusivity in healthy older adults who did not possess the APOE-ε4 allele. However, the effects of PA were reversed in older adults who were at increased genetic risk for AD, resulting in significant interactions between PA and genetic risk in several WM tracts. In the High Risk-Low PA participants, who had exhibited episodic memory decline over the previous 18-months, radial diffusivity was lower and fractional anisotropy was higher, compared to the High Risk-High PA participants. In WM tracts that subserve learning and memory processes, radial diffusivity (DR) was negatively correlated with episodic memory performance in physically inactive APOE-ε4 carriers, whereas DR was positively correlated with episodic memory performance in physically active APOE-ε4 carriers and the two Low Risk groups. The common model of demyelination-induced increase in radial diffusivity cannot directly explain these results. Rather, we hypothesize that PA may protect APOE-ε4 allele carriers from selective neurodegeneration of individual fiber populations at locations of crossing fibers within projection and association WM fiber tracts.

A review on functional and structural brain connectivity in numerical cognition.

Only recently has the complex anatomo-functional system underlying numerical cognition become accessible to evaluation in the living brain. We identified 27 studies investigating brain connectivity in numerical cognition. Despite considerable heterogeneity regarding methodological approaches, populations investigated, and assessment procedures implemented, the results provided largely converging evidence regarding the underlying brain connectivity involved in numerical cognition. Analyses of both functional/effective as well as structural connectivity have consistently corroborated the assumption that numerical cognition is subserved by a fronto-parietal network including (intra)parietal as well as (pre)frontal cortex sites. Evaluation of structural connectivity has indicated the involvement of fronto-parietal association fibers encompassing the superior longitudinal fasciculus dorsally and the external capsule/extreme capsule system ventrally. Additionally, commissural fibers seem to connect the bilateral intraparietal sulci when number magnitude information is processed. Finally, the identification of projection fibers such as the superior corona radiata indicates connections between cortex and basal ganglia as well as the thalamus in numerical cognition. Studies on functional/effective connectivity further indicated a specific role of the hippocampus. These specifications of brain connectivity augment the triple-code model of number processing and calculation with respect to how gray matter areas associated with specific number-related representations may work together.

Microstructural White Matter Abnormalities and Cognitive Dysfunction in Subcortical Ischemic Vascular Disease: an Atlas-Based Diffusion Tensor Analysis Study.

Recent studies in subcortical ischemic vascular disease (SIVD) suggest the involvement of white matter (WM) abnormalities underlying the pathogenesis of cognitive function impairment. Here, we performed magnetic resonance diffusion tensor imaging (DTI) on detecting WM damage and to investigate the correlations between DTI measures and cognitive dysfunction in SIVD patients. Fifty right-handed SIVD patients were recruited and divided into vascular cognitive impairment on dementia (VCIND) group and normal cognition (NC) group. Twenty-two VCIND patients and 28 NC patients underwent DTI scanning and neuropsychological assessment. Atlas-based analysis (ABA) was performed on each subject for extracting FA and MD measures from supratentorial tracts. Among VCIND, as compared to NC patients, decreased FA and increased MD were observed in all projection fibers (bilateral anterior, posterior limb, and retrolenticular part of internal capsule, anterior, superior, and posterior corona radiata and posterior thalamic radiation), association fibers (bilateral sagittal stratum, external capsule, cingulum, fornix, and stria terminalis, superior longitudinal fasciculus, superior fronto-occipital fasciculus, and uncinate fasciculus), and commissural fibers (genu, body, splenium, and bilateral tapetum of corpus callosum). Furthermore, we also found that MoCA scores correlated with DTI values in all supratentorial WM tracts. The results suggested that SIVD patients demonstrated abnormal WM connectivity in all supratentorial regions. Moreover, the severity of damage in WM tracts correlated with cognitive dysfunction.

Brain gray and white matter differences in healthy normal weight and obese children.

To compare brain gray and white matter development in healthy normal weight and obese children. Twenty-four healthy 8- to 10-year-old children whose body mass index was either <75(th) percentile (normal weight) or >95(th) percentile (obese) completed an MRI examination which included T1-weighted three-dimensional structural imaging and diffusion tensor imaging (DTI). Voxel-based morphometry was used to compare the regional gray and white matter between the normal weight and obese children, and tract-based spatial statistics was used to compare the water diffusion parameters in the white matter between groups. Compared with normal weight children, obese children had significant (P < 0.05, family wise error corrected) regional gray matter reduction in the right middle temporal gyrus, left and right thalami, left superior parietal gyrus, left pre/postcentral gyri, and left cerebellum. Obese children also had higher white matter (P < 0.05, corrected) in multiple regions in the brain and higher DTI measured fractional anisotropy (FA) values (P < 0.05, corrected) in part of the left brain association and projection fibers. There was no difference in mean diffusivity at P < 0.05, corrected. DTI eigenvalues suggested that the FA differences were likely from decreased radial diffusivity (P < 0.1, corrected) and there was no change in axial diffusivity (corrected P > 0.35 for all voxels). Our results indicated that obese but otherwise healthy children have different regional gray and white matter development in the brain and differences in white matter microstructures compared with healthy normal weight children.

White matter fiber tractography and quantitative analysis of diffusion tensor imaging

Magnetic resonance diffusion tensor imaging (DTI) is a noninvasive technique that can identify and quantify white matter tracts by evaluating the diffusion of water in biological tissues. While association fibers are bundles of axons within the brain that unite different parts of the same cerebral hemisphere, projection fibers are bundles of axons that unite the cortex with lower parts of the brain and the spinal cord. The commissural fibers are axon bundles that connect the two hemispheres of the brain. Quantitative analysis of DTI can be roughly classified into three types: region of interest analysis, tract-specific analysis, and fully automated hypothesis free whole brain analysis.

Self-organization of control circuits for invariant fiber projections.

Assuming that patterns in memory are represented as two-dimensional arrays of local features, just as they are in primary visual cortices, pattern recognition can take the form of elastic graph matching (Lades etal., 1993 ). Neural implementation of this may be based on preorganized fiber projections that can be activated rapidly with the help of control units (Wolfrum, Wolff, Lücke, & von der Malsburg, 2008 ). Each control unit governs a set of projection fibers that form part of a coherent mapping. We describe a mathematical model for the ontogenesis of the underlying connectivity based on a principle of network self-organization as described by the Häussler system (Häussler & von der Malsburg, 1983 ), modified to be sensitive to pattern similarity and to support formation of multiple mappings, each under the command of a control unit. The process takes the form of a soft-winner-take-all, where units compete for the representation of maps. We show simulations for invariant point-to-point and feature-to-feature mappings.