Interhemispheric functional connectivity in anorexia and bulimia nervosa

The functional interplay between hemispheres is fundamental for behavioral, cognitive, and emotional control. Anorexia nervosa (AN) and bulimia nervosa (BN) have been largely studied with brain magnetic resonance imaging (MRI) in relation to the functional mechanisms of high‐level processing, but not in terms of possible inter‐hemispheric functional connectivity anomalies. Using resting‐state functional MRI (fMRI), voxel‐mirrored homotopic connectivity (VMHC) and regional inter‐hemispheric spectral coherence (IHSC) were studied in 15 AN and 13 BN patients and 16 healthy controls (HC). Using T1‐weighted and diffusion tensor imaging MRI scans, regional VMHC values were correlated with the left‐right asymmetry of corresponding homotopic gray matter volumes and with the white matter callosal fractional anisotropy (FA). Compared to HC, AN patients exhibited reduced VMHC in cerebellum, insula, and precuneus, while BN patients showed reduced VMHC in dorso‐lateral prefrontal and orbito‐frontal cortices. The regional IHSC analysis highlighted that the inter‐hemispheric functional connectivity was higher in the ‘Slow‐5’ band in all regions except the insula. No group differences in left–right structural asymmetries and in VMHC vs. callosal FA correlations were significant in the comparisons between cohorts. These anomalies, not explained by structural changes, indicate that AN and BN, at least in their acute phase, are associated with a loss of inter‐hemispheric connectivity in regions implicated in self‐referential, cognitive control and reward processing. These findings may thus gather novel functional markers to explore aberrant features of these eating disorders.     

Parieto-frontal network in humans studied by cortico-cortical evoked potential

Parieto‐frontal network is essential for sensorimotor integration in various complex behaviors, and its disruption is associated with pathophysiology of apraxia and visuo‐spatial disorders. Despite advances in knowledge regarding specialized cortical areas for various sensorimotor transformations, little is known about the underlying cortico‐cortical connectivity in humans. We investigated inter‐areal connections of the lateral parieto‐frontal network in vivo by means of cortico‐cortical evoked potentials (CCEPs). Six patients with epilepsy and one with brain tumor were studied. With the use of subdural electrodes implanted for presurgical evaluation, network configuration was investigated by tracking the connections from the parietal stimulus site to the frontal site where the maximum CCEP was recorded. It was characterized by (i) a near‐to‐near and distant‐to‐distant, mirror symmetric configuration across the central sulcus, (ii) preserved dorso‐ventral organization (the inferior parietal lobule to the ventral premotor area and the superior parietal lobule to the dorsal premotor area), and (iii) projections to more than one frontal cortical sites in 56% of explored connections. These findings were also confirmed by the standardized parieto‐frontal CCEP connectivity map constructed in reference to the Jülich cytoarchitectonic atlas in the MNI standard space. The present CCEP study provided an anatomical blueprint underlying the lateral parieto‐frontal network and demonstrated a connectivity pattern similar to non‐human primates in the newly developed inferior parietal lobule in humans. Hum Brain Mapp, 2012. © 2011 Wiley Periodicals, Inc.     

Prefrontal cortex afferents to the anterior temporal lobe in the Macaca fascicularis monkey

The anatomical organization of the lateral prefrontal cortex (LPFC) afferents to the anterior part of the temporal lobe (ATL) remains to be clarified. The LPFC has two subdivisions, dorsal (dLPFC) and ventral (vLPFC), which have been linked to cognitive processes. The ATL includes several different cortical areas, namely, the temporal polar cortex and rostral parts of the perirhinal, inferotemporal, and anterior tip of the superior temporal gyrus cortices. Multiple sensory modalities converge in the ATL. All of them (except the rostral inferotemporal and superior temporal gyrus cortices) are components of the medial temporal lobe, which is critical for long‐term memory processing. We studied the LPFC connections with the ATL by placing retrograde tracer injections into the ATL: the temporal polar (n = 3), perirhinal (areas 35 and 36, n = 6), and inferotemporal cortices (area TE, n = 5), plus one additional deposit in the posterior parahippocampal cortex (area TF, n = 1). Anterograde tracer deposits into the dLPFC (A9 and A46, n = 2), the vLPFC (A46v, n = 2), and the orbitofrontal cortex (OF; n = 2) were placed for confirmation of those projections. The results showed that the vLPFC displays a moderate projection to rostral area TE and the dorsomedial portion of the temporal polar cortex; in contrast, the dLPFC connections with the ATL were weak. By comparison, the OFC and medial frontal cortices (MFC) showed dense connectivity with the ATL, namely, A13 with the temporopolar and perirhinal cortices. All areas of the MFC projected to the temporopolar cortex, albeit with a lower intensity. The functional significance of such paucity of LPFC afferents is unknown. J. Comp. Neurol. 523:2570–2598, 2015. © 2015 Wiley Periodicals, Inc.     

Frontal and temporal functional connections of the living human brain

Connections between human temporal and frontal cortices were investigated by intracranial electroencephalographic responses to electrical stimulation with 1-ms single pulses in 51 patients assessed for surgery for treatment of epilepsy. The areas studied were medial temporal, entorhinal, lateral temporal, medial frontal, lateral frontal and orbital frontal cortices. Findings were assumed to be representative of human brain as no differences were found between epileptogenic and non-epileptogenic hemispheres. Connections between intralobar temporal and frontal regions were common (43-95%). Connections from temporal to ipsilateral frontal regions were relatively uncommon (seen in 0-25% of hemispheres). Connections from frontal to ipsilateral temporal cortices were more common, particularly from orbital to ipsilateral medial temporal regions (40%). Contralateral temporal connections were rare (< 9%) whereas contralateral frontal connections were frequent and faster, particularly from medial frontal to contralateral medial frontal (61%) and orbital frontal cortices (57%), and between both orbital cortices (67%). Orbital cortex receives profuse connections from the ipsilateral medial (78%) and lateral (88%) frontal cortices, and from the contralateral medial (57%) and orbital (67%) frontal cortices. The high incidence of intralobar temporal connections supports the presence of temporal reverberating circuits. Frontal cortex projects within the lobe and beyond, to ipsilateral and contralateral structures.     

A direct amygdala‐motor pathway for emotional displays to influence action: A diffusion tensor imaging study

An important evolutionary function of emotions is to prime individuals for action. Although functional neuroimaging has provided evidence for such a relationship, little is known about the anatomical substrates allowing the limbic system to influence cortical motor‐related areas. Using diffusion‐weighted magnetic resonance imaging and probabilistic tractography on a cohort of 40 participants, we provide evidence of a structural connection between the amygdala and motor‐related areas (lateral and medial precentral, motor cingulate and primary motor cortices, and postcentral gyrus) in humans. We then compare this connection with the connections of the amygdala with emotion‐related brain areas (superior temporal sulcus, fusiform gyrus, orbitofrontal cortex, and lateral inferior frontal gyrus) and determine which amygdala nuclei are at the origin of these projections. Beyond the well‐known subcortical influences over automatic and stereotypical emotional behaviors, a direct amygdala‐motor pathway might provide a mechanism by which the amygdala can influence more complex motor behaviors. Hum Brain Mapp 35:5974–5983, 2014. © 2014 Wiley Periodicals, Inc.     

Intelligence‐related differences in the asymmetry of spontaneous cerebral activity

Recent evidence suggests the spontaneous BOLD signal synchronization of corresponding interhemispheric, homotopic regions as a stable trait of human brain physiology, with emerging differences in such organization being also related to some pathological conditions. To understand whether such brain functional symmetries play a role into higher‐order cognitive functioning, here we correlated the functional homotopy profiles of 119 healthy subjects with their intelligence level. Counterintuitively, reduced homotopic connectivity in above average‐IQ versus average‐IQ subjects was observed, with significant reductions in visual and somatosensory cortices, supplementary motor area, rolandic operculum, and middle temporal gyrus, possibly suggesting that a downgrading of interhemispheric talk at rest could be associated with higher cognitive functioning. These regions also showed an increased spontaneous synchrony with medial structures located in ipsi‐ and contralateral hemispheres, with such pattern being mostly detectable for regions placed in the left hemisphere. The interactions with age and gender have been also tested, with different patterns for subjects above and below 25 years old and less homotopic connectivity in the prefrontal cortex and posterior midline regions in female participants with higher IQ scores. These findings support prior evidence suggesting a functional role for homotopic connectivity in human cognitive expression, promoting the reduction of synchrony between primary sensory regions as a predictor of higher intelligence levels. Hum Brain Mapp 36:3586–3602, 2015. © 2015 Wiley Periodicals, Inc .     

Intrinsic functional connectivity variance and state‐specific under‐connectivity in autism

Autism spectrum disorder (ASD) is a neurodevelopmental condition associated with altered brain connectivity. Previous neuroimaging research demonstrates inconsistent results, particularly in studies of functional connectivity in ASD. Typically, these inconsistent findings are results of studies using static measures of resting‐state functional connectivity. Recent work has demonstrated that functional brain connections are dynamic, suggesting that static connectivity metrics fail to capture nuanced time‐varying properties of functional connections in the brain. Here we used a dynamic functional connectivity approach to examine the differences in the strength and variance of dynamic functional connections between individuals with ASD and healthy controls (HCs). The variance of dynamic functional connections was defined as the respective standard deviations of the dynamic functional connectivity strength across time. We utilized a large multicenter dataset of 507 male subjects (209 with ASD and 298 HC, from 6 to 36 years old) from the Autism Brain Imaging Data Exchange (ABIDE) to identify six distinct whole‐brain dynamic functional connectivity states. Analyses demonstrated greater variance of widespread long‐range dynamic functional connections in ASD (P < 0.05, NBS method) and weaker dynamic functional connections in ASD (P < 0.05, NBS method) within specific whole‐brain connectivity states. Hypervariant dynamic connections were also characterized by weaker connectivity strength in ASD compared with HC. Increased variance of dynamic functional connections was also related to ASD symptom severity (ADOS total score) (P < 0.05), and was most prominent in connections related to the medial superior frontal gyrus and temporal pole. These results demonstrate that greater intraindividual dynamic variance is a potential biomarker of ASD. Hum Brain Mapp 38:5740–5755, 2017. © 2017 Wiley Periodicals, Inc.     

Role of testosterone and Y chromosome genes for the masculinization of the human brain

Women with complete androgen insensitivity syndrome (CAIS) have a male (46,XY) karyotype but no functional androgen receptors. Their condition, therefore, offers a unique model for studying testosterone effects on cerebral sex dimorphism. We present MRI data from 16 women with CAIS and 32 male (46,XY) and 32 female (46,XX) controls. Methods: FreeSurfer software was employed to measure cortical thickness and subcortical structural volumes. Axonal connections, indexed by fractional anisotropy, (FA) were measured with diffusion tensor imaging, and functional connectivity with resting state fMRI. Results: Compared to men, CAIS women displayed a “female” pattern by having thicker parietal and occipital cortices, lower FA values in the right corticospinal, superior and inferior longitudinal tracts, and corpus callosum. Their functional connectivity from the amygdala to the medial prefrontal cortex, was stronger and amygdala‐connections to the motor cortex weaker than in control men. CAIS and control women also showed stronger posterior cingulate and precuneus connections in the default mode network. Thickness of the motor cortex, the caudate volume, and the FA in the callosal body followed, however, a “male” pattern. Conclusion: Altogether, these data suggest that testosterone modulates the microstructure of somatosensory and visual cortices and their axonal connections to the frontal cortex. Testosterone also influenced functional connections from the amygdala, whereas the motor cortex could, in agreement with our previous reports, be moderated by processes linked to X‐chromosome gene dosage. These data raise the question about other genetic factors masculinizing the human brain than the SRY gene and testosterone. Hum Brain Mapp 38:1801–1814, 2017. © 2017 Wiley Periodicals, Inc.     

Structural connectivity of the human anterior temporal lobe: A diffusion magnetic resonance imaging study

The anterior temporal lobes (ATL) have been implicated in a range of cognitive functions including auditory and visual perception, language, semantic knowledge, and social‐emotional processing. However, the anatomical relationships between the ATLs and the broader cortical networks that subserve these functions have not been fully elucidated. Using diffusion tensor imaging (DTI) and probabilistic tractography, we tested the hypothesis that functional segregation of information in the ATLs is reflected by distinct patterns of structural connectivity to regions outside the ATLs. We performed a parcellation of the ATLs bilaterally based on the degree of connectivity of each voxel with eight ipsilateral target regions known to be involved in various cognitive networks. Six discrete segments within each ATL showed preferential connectivity to one of the ipsilateral target regions, via four major fiber tracts (uncinate, inferior longitudinal, middle longitudinal, and arcuate fasciculi). Two noteworthy interhemispheric differences were observed: connections between the ATL and orbito‐frontal areas were stronger in the right hemisphere, while the consistency of the connection between the ATL and the inferior frontal gyrus through the arcuate fasciculus was greater in the left hemisphere. Our findings support the hypothesis that distinct regions within the ATLs have anatomical connections to different cognitive networks. Hum Brain Mapp 37:2210–2222, 2016. © 2016 Wiley Periodicals, Inc.     

Oscillatory dynamics of cortical functional connections in semantic prediction

An event related potential, known as the N400, has been particularly useful in investigating language processing as it serves as a neural index for semantic prediction. There are numerous studies on the functional segregation of N400 neural sources; however, the oscillatory dynamics of functional connections among the relevant sources has remained elusive. In this study we acquired magnetoencephalography data during a classic N400 paradigm, where the semantic predictability of a fixed target noun was manipulated in simple German sentences. We conducted inter‐regional functional connectivity (FC) and time–frequency analysis on known regions of the semantic network, encompassing bilateral temporal, and prefrontal cortices. Increased FC was found in less predicted (LP) nouns compared with highly predicted (HP) nouns in three connections: (a) right inferior frontal gyrus (IFG) and right middle temporal gyrus (MTG) from 0 to 300 ms mainly within the alpha band, (b) left lateral orbitofrontal (LOF) and right IFG around 400 ms within the beta band, and (c) left superior temporal gyrus (STG) and left LOF from 300 to 700 ms in the beta and low gamma bands. Furthermore, gamma spectral power (31–70 Hz) was stronger in HP nouns than in LP nouns in left anterior temporal cortices in earlier time windows (0–200 ms). Our findings support recent theories in language comprehension, suggesting fronto‐temporal top–down connections are mainly mediated through beta oscillations while gamma band frequencies are involved in matching between prediction and input.     

Microstructural development: Organizational differences of the fiber architecture between children and adults in dorsal and ventral visual streams

Visual perceptual skills are basically mature by the age of 7 years. White matter, however, continues to develop until late adolescence. Here, we examined children (aged 5–7 years) and adults (aged 20–30 years) using diffusion tensor imaging (DTI) fiber tracking to investigate the microstructural maturation of the visual system. We characterized the brain volumes, DTI indices, and architecture of visual fiber tracts passing through white matter structures adjacent to occipital and parietal cortex (dorsal stream), and to occipital and temporal cortex (ventral stream). Dorsal, but not ventral visual stream pathways were found to increase in volume during maturation. DTI indices revealed expected maturational differences, manifested as decreased mean and radial diffusivities and increased fractional anisotropy in both streams. Additionally, fractional anisotropy was increased and radial diffusivity was decreased in the adult dorsal stream, which can be explained by specific dorsal stream myelination or increasing fiber compaction. Adult dorsal stream architecture showed additional intra‐ and interhemispheric connections: Dorsal fibers penetrated into contralateral hemispheres via commissural structures and projection fibers extended to the superior temporal gyrus and ventral association pathways. Moreover, intra‐hemispheric connectivity was particularly strong in adult dorsal stream of the right hemisphere. Ventral stream architecture also differed between adults and children. Adults revealed additional connections to posterior lateral areas (occipital‐temporal gyrus), whereas children showed connections to posterior medial areas (posterior parahippocampal and lingual gyrus). Hence, in addition to dorsal stream myelination or fiber compaction, progressing maturation of intra‐ and interhemispheric connectivity may contribute to the development of the visual system. Hum Brain Mapp, 2011. © 2010 Wiley‐Liss, Inc.     

A combined diffusion‐weighted and electroencephalography study on age‐related differences in connectivity in the motor network during bimanual performance

We studied the relationship between age‐related differences in inter‐ and intra‐hemispheric structural and functional connectivity in the bilateral motor network. Our focus was on the correlation between connectivity and declined motor performance in older adults. Structural and functional connectivity were estimated using diffusion weighted imaging and resting‐state electro‐encephalography, respectively. A total of 48 young and older healthy participants were measured. In addition, motor performances were assessed using bimanual coordination tasks. To pre‐select regions‐of‐interest (ROIs), a neural model was adopted that accounts for intra‐hemispheric functional connectivity between dorsal premotor area (PMd) and primary motor cortex (M1) and inter‐hemispheric connections between left and right M1 (M1_L and M1_R). Functional connectivity was determined via the weighted phase‐lag index (wPLI) in the source‐reconstructed beta activity during rest. We quantified structural connectivity using kurtosis anisotropy (KA) values of tracts derived from diffusion tensor‐based fiber tractography between the aforementioned areas. In the group of older adults, wPLI values between M1_L–M1_R were negatively associated with the quality of bimanual motor performance. The additional association between wPLI values of PMd_L––M1_L and PMd_R–M1_L supports that functional connectivity with the left hemisphere mediated (bimanual) motor control in older adults. The correlational analysis between the selected structural and functional connections revealed a strong association between wPLI values in the left intra‐hemispheric PMd_L–M1_L pathway and KA values in M1_L–M1_R and PMd_R–M1_L pathways in the group of older adults. This suggests that weaker structural connections in older adults correlate with stronger functional connectivity and, hence, poorer motor performance.     

Left‐handed musicians show a higher probability of atypical cerebral dominance for language

Music processing and right hemispheric language lateralization share a common network in the right auditory cortex and its frontal connections. Given that the development of hemispheric language dominance takes place over several years, this study tested whether musicianship could increase the probability of observing right language dominance in left‐handers. Using a classic fMRI language paradigm, results showed that atypical lateralization was more predominant in musicians (40%) than in nonmusicians (5%). Comparison of left‐handers with typical left and atypical right lateralization revealed that: (a) atypical cases presented a thicker right pars triangularis and more gyrified left Heschl's gyrus; and (b) the right pars triangularis of atypical cases showed a stronger intra‐hemispheric functional connectivity with the right angular gyrus, but a weaker interhemispheric functional connectivity with part of the left Broca's area. Thus, musicianship is the first known factor related to a higher prevalence of atypical language dominance in healthy left‐handed individuals. We suggest that differences in the frontal and temporal cortex might act as shared predisposing factors to both musicianship and atypical language lateralization.     

Functional connectivity associated with hand shape generation: Imitating novel hand postures and pantomiming tool grips challenge different nodes of a shared neural network

Clinical research suggests that imitating meaningless hand postures and pantomiming tool‐related hand shapes rely on different neuroanatomical substrates. We investigated the BOLD responses to different tasks of hand posture generation in 14 right handed volunteers. Conjunction and contrast analyses were applied to select regions that were either common or sensitive to imitation and/or pantomime tasks. The selection included bilateral areas of medial and lateral extrastriate cortex, superior and inferior regions of the lateral and medial parietal lobe, primary motor and somatosensory cortex, and left dorsolateral prefrontal, and ventral and dorsal premotor cortices. Functional connectivity analysis revealed that during hand shape generation the BOLD‐response of every region correlated significantly with every other area regardless of the hand posture task performed, although some regions were more involved in some hand postures tasks than others. Based on between‐task differences in functional connectivity we predict that imitation of novel hand postures would suffer most from left superior parietal disruption and that pantomiming hand postures for tools would be impaired following left frontal damage, whereas both tasks would be sensitive to inferior parietal dysfunction. We also unveiled that posterior temporal cortex is committed to pantomiming tool grips, but that the involvement of this region to the execution of hand postures in general appears limited. We conclude that the generation of hand postures is subserved by a highly interconnected task‐general neural network. Depending on task requirements some nodes/connections will be more engaged than others and these task‐sensitive findings are in general agreement with recent lesion studies. Hum Brain Mapp 36:3426–3440, 2015. © 2015 Wiley Periodicals, Inc.     

Auditory and visual connectivity gradients in frontoparietal cortex

A frontoparietal network of brain regions is often implicated in both auditory and visual information processing. Although it is possible that the same set of multimodal regions subserves both modalities, there is increasing evidence that there is a differentiation of sensory function within frontoparietal cortex. Magnetic resonance imaging (MRI) in humans was used to investigate whether different frontoparietal regions showed intrinsic biases in connectivity with visual or auditory modalities. Structural connectivity was assessed with diffusion tractography and functional connectivity was tested using functional MRI. A dorsal–ventral gradient of function was observed, where connectivity with visual cortex dominates dorsal frontal and parietal connections, while connectivity with auditory cortex dominates ventral frontal and parietal regions. A gradient was also observed along the posterior–anterior axis, although in opposite directions in prefrontal and parietal cortices. The results suggest that the location of neural activity within frontoparietal cortex may be influenced by these intrinsic biases toward visual and auditory processing. Thus, the location of activity in frontoparietal cortex may be influenced as much by stimulus modality as the cognitive demands of a task. It was concluded that stimulus modality was spatially encoded throughout frontal and parietal cortices, and was speculated that such an arrangement allows for top–down modulation of modality‐specific information to occur within higher‐order cortex. This could provide a potentially faster and more efficient pathway by which top–down selection between sensory modalities could occur, by constraining modulations to within frontal and parietal regions, rather than long‐range connections to sensory cortices. Hum Brain Mapp 38:255–270, 2017. © 2016 Wiley Periodicals, Inc.     

Frontoparietal and default mode network connectivity varies with age and intelligence

BackgroundAnticorrelated resting state connectivity between task-positive and task-negative networks in adults supports flexible shifting between externally focused attention and internal thought. Findings suggest that children show positive correlations between task-positive (frontoparietal; FP) and task-negative (default mode; DMN) networks. FP-DMN connectivity also associates with intellectual functioning across the lifespan. We investigated whether FP-DMN connectivity in healthy children varied with age and intelligence quotient (IQ).MethodsWe utilized network-based statistics (NBS) to examine resting state functional connectivity between FP and DMN seeds in N = 133 7−25-year-olds (M_age = 15.80). Linear regression evaluated FP-DMN associations with IQ.ResultsWe detected NBS subnetworks containing both within- and between-network connections that were inversely associated with age. Four FP-DMN connections showed more negative connectivity between FP (inferior frontal gyrus and precentral gyrus) and DMN regions (frontal medial cortex, precuneus, and frontal pole) among older participants. Frontal pole-precentral gyrus connectivity inversely associated with IQ.ConclusionsFP-DMN connectivity was more anticorrelated at older ages, potentially indicating dynamic network segregation of these circuits from childhood to early adulthood. Youth with more mature (i.e., anticorrelated) FP-DMN connectivity demonstrated higher IQ. Our findings add to the growing body of literature examining neural network development and its association with IQ.     

A surface‐based technique for mapping homotopic interhemispheric connectivity: Development,characterization, and clinical application

The functional organization of the human brain consists of a high degree of connectivity between interhemispheric homologous regions. The degree of homotopic organization is known to vary across the cortex and homotopic connectivity is high in regions that share cross‐hemisphere structural connections or are activated by common input streams (e.g., the visual system). Damage to one or both regions, as well as damage to the connections between homotopic regions, could disrupt this functional organization. Here were introduce and test a computationally efficient technique, surface‐based homotopic interhermispheric connectivity (sHIC), that leverages surface‐based registration and processing techniques in an attempt to improve the spatial specificity and accuracy of cortical interhemispheric connectivity estimated with resting state functional connectivity. This technique is shown to be reliable both within and across subjects. sHIC is also characterized in a dataset of nearly 1000 subjects. We confirm previous results showing increased interhemispheric connectivity in primary sensory regions, and reveal a novel rostro‐caudal functionally defined network level pattern of sHIC across the brain. In addition, we demonstrate a structural–functional relationship between sHIC and atrophy of the corpus callosum in multiple sclerosis (r = 0.2979, p = 0.0461). sHIC presents as a sensitive and reliable measure of cortical homotopy that may prove useful as a biomarker in neurologic disease. Hum Brain Mapp 37:2849–2868, 2016. © 2016 Wiley Periodicals, Inc.     

The duality of the cingulate gyrus in monkey. Neuroanatomical study and functional hypothesis

According to most behavioural, electrophysiological, and clinical studies, the cingulate gyrus is widely thought to be involved in regulation of emotional life, reactivity to painful stimuli, memory processing, and attention to sensory stimuli. Anatomically the cingulate cortex is composed of two distinct areas numbered 24 and 23 in Brodmann's classification. We have investigated the connections of the cingulate gyrus in monkeys, using horseradish peroxydase and radioautographic techniques, in order to verify the hypothesis of an anatomical complementarity of these cytoarchitectonic subdivisions. The posterior cingulate gyrus (area 23) is specifically connected with the associative temporal cortex, the medial temporal and orbitofrontal cortices, and with the medial pulvinar. The anterior cingulate gyrus (area 24) is related to the intralaminar, mediodorsal, and ventral anterior thalamic nuclei, the amygdala, and the nucleus accumbens septi. The two cingulate areas were found to be interconnected and to have, in common, connections with the 'limbic' thalamic nuclei (AM, AV, LD), the caudate nucleus, the claustrum, the lateral frontal and the posterior parietal (area 7) cortices.     

Default‐mode network functional connectivity is closely related to metabolic activity

Over the last decade, the brain's default‐mode network (DMN) and its function has attracted a lot of attention in the field of neuroscience. However, the exact underlying mechanisms of DMN functional connectivity, or more specifically, the blood‐oxygen level‐dependent (BOLD) signal, are still incompletely understood. In the present study, we combined 2‐deoxy‐2‐[¹⁸F]fluoroglucose positron emission tomography (FDG‐PET), proton magnetic resonance spectroscopy (¹H‐MRS), and resting‐state functional magnetic resonance imaging (rs‐fMRI) to investigate more directly the association between local glucose consumption, local glutamatergic neurotransmission and DMN functional connectivity during rest. The results of the correlation analyzes using the dorsal posterior cingulate cortex (dPCC) as seed region showed spatial similarities between fluctuations in FDG‐uptake and fluctuations in BOLD signal. More specifically, in both modalities the same DMN areas in the inferior parietal lobe, angular gyrus, precuneus, middle, and medial frontal gyrus were positively correlated with the dPCC. Furthermore, we could demonstrate that local glucose consumption in the medial frontal gyrus, PCC and left angular gyrus was associated with functional connectivity within the DMN. We did not, however, find a relationship between glutamatergic neurotransmission and functional connectivity. In line with very recent findings, our results lend further support for a close association between local metabolic activity and functional connectivity and provide further insights towards a better understanding of the underlying mechanism of the BOLD signal. Hum Brain Mapp 36:2027–2038, 2015. © 2015 Wiley Periodicals, Inc.     

Inner Hemispheric and Interhemispheric Connectivity Balance in the Human Brain

The connectome of the brain has a great impact on the function of the brain as the structure of the connectome affects the speed and efficiency of information transfer. As a highly energy-consuming organ, an efficient network structure is essential. A previous study has shown consistent overall brain connectivity across a large variety of species. This connectivity conservation was explained by a balance between interhemispheric and intrahemispheric connections; that is, spices with highly connected hemispheres appear to have weaker interhemisphere connections. This study examines this connectivity trade-off in the human brain using diffusion-based tractography and network analysis in the Human Connectome Project (970 subjects, 527 female). We explore the biological origins of this phenomenon, heritability, and the effect on cognitive measures.The proportion of commissural fibers in the brain had a negative correlation to hemispheric efficiency, pointing to a trade-off between inner hemispheric and interhemispheric connectivity. Network hubs including anterior and middle cingulate cortex, superior frontal areas, medial occipital areas, the parahippocampal gyrus, post- and precentral gyri, and the precuneus had the strongest contribution to this phenomenon. Other results show a high heritability as well as a strong connection to crystalized intelligence. This work presents cohort-based network analysis research, spanning a large variety of samples and exploring the overall architecture of the human connectome. Our results show a connectivity conservation phenomenon at the base of the overall brain network architecture. This network structure may explain much of the functional, behavioral, and cognitive variability among different brains.SIGNIFICANCE STATEMENT The network structure of the brain is at the basis of every brain function as it dictates the characteristics of information transfer. Understanding the patterns and mechanisms that guide the connectome structure is crucial to understanding the brain itself. Here we unravel the mechanism at the base of the connectivity conservation phenomenon by exploring the interaction between hemispheric and commissural connectivity in a large-scale cohort-based connectivity study. We describe the trade-off between the two components and examine the origins of the trade-off and observe the effect on cognitive abilities and behavior.