Altered resting perfusion and functional connectivity of default mode network in youth with autism spectrum disorder.
Brain Behav. 2015 Sep;5(9):e00358
Authors: Jann K, Hernandez LM, Beck-Pancer D, McCarron R, Smith RX, Dapretto M, Wang DJ
BACKGROUND: Neuroimaging studies can shed light on the neurobiological underpinnings of autism spectrum disorders (ASD). Studies of the resting brain have shown both altered baseline metabolism from PET/SPECT and altered functional connectivity (FC) of intrinsic brain networks based on resting-state fMRI. To date, however, no study has investigated these two physiological parameters of resting brain function jointly, or explored the relationship between these measures and ASD symptom severity.
METHODS: Here, we used pseudo-continuous arterial spin labeling with 3D background-suppressed GRASE to assess resting cerebral blood flow (CBF) and FC in 17 youth with ASD and 22 matched typically developing (TD) children.
RESULTS: A pattern of altered resting perfusion was found in ASD versus TD children including frontotemporal hyperperfusion and hypoperfusion in the dorsal anterior cingulate cortex. We found increased local FC in the anterior module of the default mode network (DMN) accompanied by decreased CBF in the same area. In our cohort, both alterations were associated with greater social impairments as assessed with the Social Responsiveness Scale (SRS-total T scores). While FC was correlated with CBF in TD children, this association between FC and baseline perfusion was disrupted in children with ASD. Furthermore, there was reduced long-range FC between anterior and posterior modules of the DMN in children with ASD.
CONCLUSION: Taken together, the findings of this study - the first to jointly assess resting CBF and FC in ASD - highlight new avenues for identifying novel imaging markers of ASD symptomatology.
PMID: 26445698 [PubMed - as supplied by publisher]
Altered connectivity of the dorsal and ventral visual regions in dyslexic children: a resting-state fMRI study.
Front Hum Neurosci. 2015;9:495
Authors: Zhou W, Xia Z, Bi Y, Shu H
While there is emerging evidence from behavioral studies that visual attention skills are impaired in dyslexia, the corresponding neural mechanism (i.e., deficits in the dorsal visual region) needs further investigation. We used resting-state fMRI to explore the functional connectivity (FC) patterns of the left intraparietal sulcus (IPS) and the visual word form area (VWFA) in dyslexic children (N = 21, age mean = 12) and age-matched controls (N = 26, age mean = 12). The results showed that the left IPS and the VWFA were functionally connected to each other in both groups and that both were functionally connected to left middle frontal gyrus (MFG). Importantly, we observed significant group differences in FC between the left IPS and the left MFG and between the VWFA and the left MFG. In addition, the strengths of the identified FCs were significantly correlated with the score of fluent reading, which required obvious eye movement and visual attention processing, but not with the lexical decision score. We conclude that dyslexics have deficits in the network composed of the prefrontal, dorsal visual and ventral visual regions and may have a lack of modulation from the left MFG to the dorsal and ventral visual regions.
PMID: 26441595 [PubMed - as supplied by publisher]
Resting state functional connectivity differences between behavioral variant frontotemporal dementia and Alzheimer's disease.
Front Hum Neurosci. 2015;9:474
Authors: Hafkemeijer A, Möller C, Dopper EG, Jiskoot LC, Schouten TM, van Swieten JC, van der Flier WM, Vrenken H, Pijnenburg YA, Barkhof F, Scheltens P, van der Grond J, Rombouts SA
Introduction: Alzheimer's disease (AD) and behavioral variant frontotemporal dementia (bvFTD) are the most common types of early-onset dementia. Early differentiation between both types of dementia may be challenging due to heterogeneity and overlap of symptoms. Here, we apply resting state functional magnetic resonance imaging (fMRI) to study functional brain connectivity differences between AD and bvFTD. Methods: We used resting state fMRI data of 31 AD patients, 25 bvFTD patients, and 29 controls from two centers specialized in dementia. We studied functional connectivity throughout the entire brain, applying two different analysis techniques, studying network-to-region and region-to-region connectivity. A general linear model approach was used to study group differences, while controlling for physiological noise, age, gender, study center, and regional gray matter volume. Results: Given gray matter differences, we observed decreased network-to-region connectivity in bvFTD between (a) lateral visual cortical network and lateral occipital and cuneal cortex, and (b) auditory system network and angular gyrus. In AD, we found decreased network-to-region connectivity between the dorsal visual stream network and lateral occipital and parietal opercular cortex. Region-to-region connectivity was decreased in bvFTD between superior temporal gyrus and cuneal, supracalcarine, intracalcarine cortex, and lingual gyrus. Conclusion: We showed that the pathophysiology of functional brain connectivity is different between AD and bvFTD. Our findings support the hypothesis that resting state fMRI shows disease-specific functional connectivity differences and is useful to elucidate the pathophysiology of AD and bvFTD. However, the group differences in functional connectivity are less abundant than has been shown in previous studies.
PMID: 26441584 [PubMed - as supplied by publisher]
BASCO: a toolbox for task-related functional connectivity.
Front Syst Neurosci. 2015;9:126
Authors: Göttlich M, Beyer F, Krämer UM
BASCO (BetA Series COrrelation) is a user-friendly MATLAB toolbox with a graphical user interface (GUI) which allows investigating functional connectivity in event-related functional magnetic resonance imaging (fMRI) data. Connectivity analyses extend and compliment univariate activation analyses since the actual interaction between brain regions involved in a task can be explored. BASCO supports seed-based functional connectivity as well as brain network analyses. Although there are a multitude of advanced toolboxes for investigating resting-state functional connectivity, BASCO is the first toolbox for evaluating task-related whole-brain functional connectivity employing a large number of network nodes. Thus, BASCO allows investigating task-specific rather than resting-state networks. Here, we summarize the main features of the toolbox and describe the methods and algorithms.
PMID: 26441558 [PubMed - as supplied by publisher]
Asymmetric projections of the arcuate fasciculus to the temporal cortex underlie lateralized language function in the human brain.
Front Neuroanat. 2015;9:119
Authors: Takaya S, Kuperberg GR, Liu H, Greve DN, Makris N, Stufflebeam SM
The arcuate fasciculus (AF) in the human brain has asymmetric structural properties. However, the topographic organization of the asymmetric AF projections to the cortex and its relevance to cortical function remain unclear. Here we mapped the posterior projections of the human AF in the inferior parietal and lateral temporal cortices using surface-based structural connectivity analysis based on diffusion MRI and investigated their hemispheric differences. We then performed the cross-modal comparison with functional connectivity based on resting-state functional MRI (fMRI) and task-related cortical activation based on fMRI using a semantic classification task of single words. Structural connectivity analysis showed that the left AF connecting to Broca's area predominantly projected in the lateral temporal cortex extending from the posterior superior temporal gyrus to the mid part of the superior temporal sulcus and the middle temporal gyrus, whereas the right AF connecting to the right homolog of Broca's area predominantly projected to the inferior parietal cortex extending from the mid part of the supramarginal gyrus to the anterior part of the angular gyrus. The left-lateralized projection regions of the AF in the left temporal cortex had asymmetric functional connectivity with Broca's area, indicating structure-function concordance through the AF. During the language task, left-lateralized cortical activation was observed. Among them, the brain responses in the temporal cortex and Broca's area that were connected through the left-lateralized AF pathway were specifically correlated across subjects. These results suggest that the human left AF, which structurally and functionally connects the mid temporal cortex and Broca's area in asymmetrical fashion, coordinates the cortical activity in these remote cortices during a semantic decision task. The unique feature of the left AF is discussed in the context of the human capacity for language.
PMID: 26441551 [PubMed - as supplied by publisher]
An empirical Bayes normalization method for connectivity metrics in resting state fMRI.
Front Neurosci. 2015;9:316
Authors: Chen S, Kang J, Wang G
Functional connectivity analysis using resting-state functional magnetic resonance imaging (rs-fMRI) has emerged as a powerful technique for investigating functional brain networks. The functional connectivity is often quantified by statistical metrics (e.g., Pearson correlation coefficient), which may be affected by many image acquisition and preprocessing steps such as the head motion correction and the global signal regression. The appropriate quantification of the connectivity metrics is essential for meaningful and reproducible scientific findings. We propose a novel empirical Bayes method to normalize the functional brain connectivity metrics on a posterior probability scale. Moreover, the normalization function maps the original connectivity metrics to values between zero and one, which is well-suited for the graph theory based network analysis and avoids the information loss due to the (negative value) hard thresholding step. We apply the normalization method to a simulation study and the simulation results show that our normalization method effectively improves the robustness and reliability of the quantification of brain functional connectivity and provides more powerful group difference (biomarkers) detection. We illustrate our method on an analysis of a rs-fMRI dataset from the Autism Brain Imaging Data Exchange (ABIDE) study.
PMID: 26441493 [PubMed - as supplied by publisher]
Reductions in Cortico-Striatal Hyperconnectivity Accompany Successful Treatment of Obsessive-Compulsive Disorder with Dorsomedial Prefrontal rTMS.
Neuropsychopharmacology. 2015 Oct 6;
Authors: Dunlop K, Woodside B, Olmsted M, Colton P, Giacobbe P, Downar J
Obsessive-compulsive disorder (OCD) is a disabling illness with high rates of non-response to conventional treatments. OCD pathophysiology is believed to involve abnormalities in cortico-striatal-thalamic-cortical circuits through regions such as dorsomedial prefrontal cortex (dmPFC), and ventral striatum. These regions may constitute therapeutic targets for neuromodulation treatments, such as repetitive transcranial magnetic stimulation (rTMS). However, the neurobiological predictors and correlates of successful rTMS treatment for OCD are unclear. Here, we used resting-state functional magnetic resonance imaging (fMRI) to identify neural predictors and correlates of response to 20-30 sessions of bilateral 10 Hz dmPFC-rTMS in 20 treatment-resistant OCD patients, with 40 healthy controls as baseline comparators. A region of interest in the dmPFC was used to generate whole-brain functional connectivity maps pre- and post-treatment. 10 of 20 patients met response criteria (⩾50% improvement on Yale-Brown Obsessive-Compulsive Scale, YBOCS); response to dmPFC-rTMS was sharply bimodal. dmPFC-rTMS responders had higher dmPFC-ventral striatal connectivity at baseline. The degree of reduction in this connectivity, from pre- to post-treatment, correlated to the degree of YBOCS symptomatic improvement. Baseline clinical and psychometric data did not predict treatment response. In summary, reductions in fronto-striatal hyperconnectivity were associated with treatment response to dmPFC-rTMS in OCD. This finding is consistent with previous fMRI studies of deep brain stimulation in OCD, but opposite to previous reports on mechanisms of dmPFC-rTMS in major depression. fMRI could prove useful in predicting response to dmPFC-rTMS in OCD.Neuropsychopharmacology accepted article preview online, 06 October 2015. doi:10.1038/npp.2015.292.
PMID: 26440813 [PubMed - as supplied by publisher]
Role of mitochondrial calcium uptake homeostasis in resting state fMRI brain networks.
NMR Biomed. 2015 Oct 6;
Authors: Kannurpatti SS, Sanganahalli BG, Herman P, Hyder F
Mitochondrial Ca(2+) uptake influences both brain energy metabolism and neural signaling. Given that brain mitochondrial organelles are distributed in relation to vascular density, which varies considerably across brain regions, we hypothesized different physiological impacts of mitochondrial Ca(2+) uptake across brain regions. We tested the hypothesis by monitoring brain "intrinsic activity" derived from the resting state functional MRI (fMRI) blood oxygen level dependent (BOLD) fluctuations in different functional networks spanning the somatosensory cortex, caudate putamen, hippocampus and thalamus, in normal and perturbed mitochondrial Ca(2+) uptake states. In anesthetized rats at 11.7 T, mitochondrial Ca(2+) uptake was inhibited or enhanced respectively by treatments with Ru360 or kaempferol. Surprisingly, mitochondrial Ca(2+) uptake inhibition by Ru360 and enhancement by kaempferol led to similar dose-dependent decreases in brain-wide intrinsic activities in both the frequency domain (spectral amplitude) and temporal domain (resting state functional connectivity; RSFC). The fact that there were similar dose-dependent decreases in the frequency and temporal domains of the resting state fMRI-BOLD fluctuations during mitochondrial Ca(2+) uptake inhibition or enhancement indicated that mitochondrial Ca(2+) uptake and its homeostasis may strongly influence the brain's functional organization at rest. Interestingly, the resting state fMRI-derived intrinsic activities in the caudate putamen and thalamic regions saturated much faster with increasing dosage of either drug treatment than the drug-induced trends observed in cortical and hippocampal regions. Regional differences in how the spectral amplitude and RSFC changed with treatment indicate distinct mitochondrion-mediated spontaneous neuronal activity coupling within the various RSFC networks determined by resting state fMRI. Copyright © 2015 John Wiley & Sons, Ltd.
PMID: 26439799 [PubMed - as supplied by publisher]
Altered resting-state functional connectivity in late-life depression: A cross-sectional study.
J Affect Disord. 2015 Sep 28;189:126-133
Authors: Eyre HA, Yang H, Leaver AM, Van Dyk K, Siddarth P, Cyr NS, Narr K, Ercoli L, Baune BT, Lavretsky H
BACKGROUND: Disrupted brain connectivity is implicated in the pathophysiology of late-life depression (LLD). There are few studies in this area using resting-state functional magnetic resonance imaging (rs-fMRI). In this pilot case-control study, we compare rs-fMRI data between age-matched depressed and non-depressed older adults.
METHODS: Older participants (≥55 years) with current major depressive disorder (MDD) were recruited to participate in an ongoing study of LLD, and were compared to the age-matched, non-depressed controls. Rs-fMRI data were collected using a 3-Tesla MRI system. In this study, a data-driven approach was chosen and an independent component analysis (ICA) was performed.
RESULTS: Seventeen subjects with MDD were compared to 31 controls. The depressed group showed increased connectivity in three main networks compared to the controls (p(corr)<0.05), including connectivity between the default mode network (DMN) and the posterior superior temporal sulcus (pSTS). Increased connectivity was also observed within the visual network in the medial, lateral and ventral regions of the occipital lobes, and within the auditory network throughout the right superior temporal cortex.
CONCLUSION: This data-driven, pilot study finds patterns of increased connectivity that may be unique to LLD in the DMN, as well as visual and auditory networks. The functional implications of this aberrant connectivity remains to be determined. These findings should be further explored in larger samples.
PMID: 26433760 [PubMed - as supplied by publisher]
Tonic Local Brain Blood Flow Control by Astrocytes Independent of Phasic Neurovascular Coupling.
J Neurosci. 2015 Sep 30;35(39):13463-74
Authors: Rosenegger DG, Tran CH, Wamsteeker Cusulin JI, Gordon GR
UNLABELLED: According to the current model of neurovascular coupling, blood flow is controlled regionally through phasic changes in the activity of neurons and astrocytes that signal to alter arteriole diameter. Absent in this model, however, is how brain blood flow is tonically regulated independent of regional changes in activity. This is important because a large fraction of brain blood flow is required to maintain basal metabolic needs. Using two-photon fluorescence imaging combined with patch-clamp in acute rat brain slices of sensory-motor cortex, we demonstrate that reducing resting Ca(2+) in astrocytes with intracellular BAPTA causes vasoconstriction in adjacent arterioles. BAPTA-induced vasoconstriction was eliminated by a general COX blocker and the effect is mimicked by a COX-1, but not COX-2, antagonist, suggesting that astrocytes provide tonic, steady-state vasodilation by releasing prostaglandin messengers. Tonic vasodilation was insensitive to TTX, as well as a variety of synaptic and extrasynaptic receptor antagonists, indicating that the phenomenon operates largely independent of neural activity. Using in vivo two-photon fluorescence imaging of the barrel cortex in fully awake mice, we reveal that acute COX-1 inhibition reduces resting arteriole diameter but fails to affect vasodilation in response to vibrissae stimulation. Our findings demonstrate that astrocytes provide tonic regulation of arterioles using resting intracellular Ca(2+) in a manner that is independent of phasic, neuronal-evoked vasodilation.
SIGNIFICANCE STATEMENT: The brain requires both phasic and tonic regulation of its blood supply to service energy needs over various temporal windows. While many mechanisms have been described for phasic blood flow regulation, how the brain accomplishes tonic control is largely unknown. Here we describe a way in which astrocytes contribute to the management of basal brain blood flow by providing steady-state vasodilation to arterioles via resting astrocyte Ca(2+) and the continuous release of prostaglandin messengers. This phenomenon may be important for understanding the declines in basal brain blood flow that occur in aging and dementia, as well as for the interpretation of fMRI data.
PMID: 26424891 [PubMed - in process]
Exploring brain functional plasticity in world class gymnasts: a network analysis.
Brain Struct Funct. 2015 Sep 29;
Authors: Wang J, Lu M, Fan Y, Wen X, Zhang R, Wang B, Ma Q, Song Z, He Y, Wang J, Huang R
Long-term motor skill learning can induce plastic structural and functional reorganization of the brain. Our previous studies detected brain structural plasticity related to long-term intensive gymnastic training in world class gymnasts (WCGs). The goal of this study was to investigate brain functional plasticity in WCGs by using network measures of brain functional networks. Specifically, we acquired resting-state fMRI data from 13 WCGs and 14 controls, constructed their brain functional networks, and compared the differences in their network parameters. At the whole brain level, we detected significantly decreased overall functional connectivity (FC) and decreased local and global efficiency in the WCGs compared to the controls. At the modular level, we found intra- and inter-modular reorganization in three modules, the cerebellum, the cingulo-opercular and fronto-parietal networks, in the WCGs. On the nodal level, we revealed significantly decreased nodal strength and efficiency in several non-rich club regions of these three modules in the WCGs. These results suggested that functional plasticity can be detected in the brain functional networks of WCGs, especially in the cerebellum, fronto-parietal network, and cingulo-opercular network. In addition, we found that the FC between the fronto-parietal network and the sensorimotor network was significantly negatively correlated with the number of years of training in the WCGs. These findings may help us to understand the outstanding gymnastic performance of the gymnasts and to reveal the neural mechanisms that distinguish WCGs from controls.
PMID: 26420277 [PubMed - as supplied by publisher]
Evidence of a dissociation pattern in default mode subnetwork functional connectivity in schizophrenia.
Sci Rep. 2015;5:14655
Authors: Wang H, Zeng LL, Chen Y, Yin H, Tan Q, Hu D
The default mode network (DMN) is suggested to play a pivotal role in schizophrenia; however, the dissociation pattern of functional connectivity of DMN subsystems remains uncharacterized in this disease. In this study, resting-state fMRI data were acquired from 55 schizophrenic patients and 53 matched healthy controls. DMN connectivity was estimated from time courses of independent components. The lateral DMN exhibited decreased connectivity with the unimodal sensorimotor cortex but increased connectivity with the heteromodal association areas in schizophrenics. The increased connectivity between the lateral DMN and right control network was significantly correlated with negative and anergia factor scores in the schizophrenic patients. The anterior and posterior DMNs exhibited increased and decreased connectivity with the right control and lateral visual networks, respectively, in schizophrenics. The altered DMN connectivity may underlie the hallucinations, delusions, thought disturbances, and negative symptoms involved in schizophrenia. Furthermore, DMN connectivity patterns could be used to differentiate patients from controls with 76.9% accuracy. These findings may shed new light on the distinct role of DMN subsystems in schizophrenia, thereby furthering our understanding of the pathophysiology of schizophrenia. Elucidating key disease-related DMN subsystems is critical for identifying treatment targets and aiding in the clinical diagnosis and development of treatment strategies.
PMID: 26419213 [PubMed - in process]
Correction: Reduced Topological Efficiency in Cortical-Basal Ganglia Motor Network of Parkinson's Disease: A Resting State fMRI Study.
PLoS One. 2015;10(9):e0139757
Authors: Wei L, Zhang J, Long Z, Wu GR, Hu X, Zhang Y, Wang J
[This corrects the article DOI: 10.1371/journal.pone.0108124.].
PMID: 26417947 [PubMed - as supplied by publisher]
In search of neural mechanisms of mirror neuron dysfunction in schizophrenia: resting state functional connectivity approach.
Psychiatr Danub. 2015 Sep;27(Suppl-1):269-272
Authors: Zaytseva Y, Bendova M, Garakh Z, Tintera J, Rydlo J, Spaniel F, Horacek J
It has been repeatedly shown that schizophrenia patients have immense alterations in goal-directed behaviour, social cognition, and social interactions, cognitive abilities that are presumably driven by the mirror neurons system (MNS). However, the neural bases of these deficits still remain unclear. Along with the task-related fMRI and EEG research tapping into the mirror neuron system, the characteristics of the resting state activity in the particular areas that encompass mirror neurons might be of interest as they obviously determine the baseline of the neuronal activity. Using resting state fMRI, we investigated resting state functional connectivity (FC) in four predefined brain structures, ROIs (inferior frontal gyrus, superior parietal lobule, premotor cortex and superior temporal gyrus), known for their mirror neurons activity, in 12 patients with first psychotic episode and 12 matched healthy individuals. As a specific hypothesis, based on the knowledge of the anatomical inputs of thalamus to all preselected ROIs, we have investigated the FC between thalamus and the ROIs. Of all ROIs included, seed-to-voxel connectivity analysis revealed significantly decreased FC only in left posterior superior temporal gyrus (STG) and the areas in visual cortex and cerebellum in patients as compared to controls. Using ROI-to-ROI analysis (thalamus and selected ROIs), we have found an increased FC of STG and bilateral thalamus whereas the FC of these areas was decreased in controls. Our results suggest that: (1) schizophrenia patients exhibit FC of STG which corresponds to the previously reported changes of superior temporal gyrus in schizophrenia and might contribute to the disturbances of specific functions, such as emotional processing or spatial awareness; (2) as the thalamus plays a pivotal role in the sensory gating, providing the filtering of the redundant stimulation, the observed hyperconnectivity between the thalami and the STGs in patients with schizophrenia might explain the sequential overload with sensory inputs that leads to the abnormal cognitive processing.
PMID: 26417778 [PubMed - as supplied by publisher]
FIACH: A Biophysical Model for Automatic Retrospective Noise Control in fMRI.
Neuroimage. 2015 Sep 25;
Authors: Tierney TM, Croft LJ, Centeno M, Shamshiri EA, Perani S, Baldeweg T, Clark CA, Carmichael DW
Different noise sources in fMRI acquisition can lead to spurious false positives and reduced sensitivity. We have developed a biophysically-based model (named FIACH: Functional Image Artefact Correction Heuristic) which extends current retrospective noise control methods in fMRI. FIACH can be applied to both General Linear Model (GLM) and resting state functional connectivity MRI (rs-fcMRI) studies. FIACH is a two-step procedure involving the identification and correction of non-physiological large amplitude temporal signal changes and spatial regions of high temporal instability. We have demonstrated its efficacy in a sample of 42 healthy children while performing language tasks that include overt speech with known activations. We demonstrate large improvements in sensitivity when FIACH is compared with current methods of retrospective correction. FIACH reduces the confounding effects of noise and increases the study's power by explaining significant variance that is not contained within the commonly used motion parameters. The method is particularly useful in detecting activations in inferior temporal regions which have proven problematic for fMRI. We have shown greater reproducibility and robustness of fMRI responses using FIACH in the context of task induced motion. In a clinical setting this will translate to increasing the reliability and sensitivity of fMRI used for the identification of language lateralisation and eloquent cortex. FIACH can benefit studies of cognitive development in young children, patient populations and older adults.
PMID: 26416652 [PubMed - as supplied by publisher]
Vascular Autorescaling of fMRI (VasA fMRI) Improves Sensitivity of Population Studies: A Pilot Study.
Neuroimage. 2015 Sep 25;
Authors: Kazan SM, Mohammadi S, Callaghan MF, Flandin G, Huber L, Leech R, Kennerley A, Windischberger C, Weiskopf N
The blood oxygenation level dependent (BOLD) signal is widely used for functional magnetic resonance imaging (fMRI) of brain function in health and disease. The statistical power of fMRI group studies is significantly hampered by high inter-subject variance due to differences in baseline vascular physiology. Several methods have been proposed to account for physiological vascularization differences between subjects and hence improve the sensitivity in group studies. However, these methods require the acquisition of additional reference scans (such as a full resting-state fMRI session or ASL based calibrated BOLD). We present a vascular autorescaling (VasA) method, which does not require any additional reference scans. VasA is based on the observation that slow oscillations (<0.1 Hz) in arterial blood CO2 levels occur naturally due to changes in respiration patterns. These oscillations yield fMRI signal changes whose amplitudes reflect the blood oxygenation levels and underlying local vascularization and vascular responsivity. VasA estimates proxies of the amplitude of these CO2-driven oscillations directly from the residuals of task-related fMRI data without the need for reference scans. The estimates are used to scale the amplitude of task-related fMRI responses, to account for vascular differences. The VasA maps compared well to cerebrovascular reactivity (CVR) maps and cerebral blood volume maps based on VAscular Space Occupancy (VASO) measurements in four volunteers, speaking to the physiological vascular basis of VasA. VasA was validated in a wide variety of tasks in 138 volunteers. VasA increased t-scores by up to 30% in specific brain areas such as the visual cortex. The number of activated voxels was increased by up to 200% in brain areas such as the orbital frontal cortex while still controlling the nominal false positive rate. VasA fMRI outperformed previously proposed rescaling approaches based on resting-state fMRI data and can be readily applied to any task-related fMRI dataset, even retrospectively.
PMID: 26416648 [PubMed - as supplied by publisher]
A parsimonious statistical method to detect groupwise differentially expressed functional connectivity networks.
Hum Brain Mapp. 2015 Sep 29;
Authors: Chen S, Kang J, Xing Y, Wang G
Group-level functional connectivity analyses often aim to detect the altered connectivity patterns between subgroups with different clinical or psychological experimental conditions, for example, comparing cases and healthy controls. We present a new statistical method to detect differentially expressed connectivity networks with significantly improved power and lower false-positive rates. The goal of our method was to capture most differentially expressed connections within networks of constrained numbers of brain regions (by the rule of parsimony). By virtue of parsimony, the false-positive individual connectivity edges within a network are effectively reduced, whereas the informative (differentially expressed) edges are allowed to borrow strength from each other to increase the overall power of the network. We develop a test statistic for each network in light of combinatorics graph theory, and provide p-values for the networks (in the weak sense) by using permutation test with multiple-testing adjustment. We validate and compare this new approach with existing methods, including false discovery rate and network-based statistic, via simulation studies and a resting-state functional magnetic resonance imaging case-control study. The results indicate that our method can identify differentially expressed connectivity networks, whereas existing methods are limited. Hum Brain Mapp, 2015. © 2015 Wiley Periodicals, Inc.
PMID: 26416398 [PubMed - as supplied by publisher]
Reward breaks through center-surround inhibition via anterior insula.
Hum Brain Mapp. 2015 Sep 29;
Authors: Wang L, Yu H, Hu J, Theeuwes J, Gong X, Xiang Y, Jiang C, Zhou X
Focusing attention on a target creates a center-surround inhibition such that distractors located close to the target do not capture attention. Recent research showed that a distractor can break through this surround inhibition when associated with reward. However, the brain basis for this reward-based attention is unclear. In this fMRI study, we presented a distractor associated with high or low reward at different distances from the target. Behaviorally the low-reward distractor did not capture attention and thus did not cause interference, whereas the high-reward distractor captured attention only when located near the target. Neural activity in extrastriate cortex mirrored the behavioral pattern. A comparison between the high-reward and the low-reward distractors presented near the target (i.e., reward-based attention) and a comparison between the high-reward distractors located near and far from the target (i.e., spatial attention) revealed a common frontoparietal network, including inferior frontal gyrus and inferior parietal sulcus as well as the visual cortex. Reward-based attention specifically activated the anterior insula (AI). Dynamic causal modelling showed that reward modulated the connectivity from AI to the frontoparietal network but not the connectivity from the frontoparietal network to the visual cortex. Across participants, the reward-based attentional effect could be predicted both by the activity in AI and by the changes of spontaneous functional connectivity between AI and ventral striatum before and after reward association. These results suggest that AI encodes reward-based salience and projects it to the stimulus-driven attentional network, which enables the reward-associated distractor to break through the surround inhibition in the visual cortex. Hum Brain Mapp, 2015. © 2015 Wiley Periodicals, Inc.
PMID: 26416017 [PubMed - as supplied by publisher]
Neural networks of tinnitus in humans: Elucidating severity and habituation.
Hear Res. 2015 Sep 25;
Authors: Husain FT
The article reviews current data about the neural correlates of an individual's reaction to tinnitus, primarily from studies that employ magnetic resonance imaging (MRI). Human studies employing brain imaging remain the most commonly used method to understand neural biomarkers of the reaction to tinnitus, a subjective hearing disorder. Evidence from anatomical and functional MRI studies is reviewed to better understand the large-scale neural networks implicated in tinnitus habituation and severity. These networks are concerned with attention, audition, and emotion, both during tasks and at 'rest' when no goal-directed activity is expected. I place the data in the context of published literature and current theories about tinnitus severity, while explaining the challenges and limitations of human MRI studies. A possible model of habituation to tinnitus is described, that of the attention system (via the frontal cortex) suppressing the response from the amygdala and the use of alternate nodes of the limbic system such as the insula and the parahippocampal gyrus when mediating emotion.
PMID: 26415997 [PubMed - as supplied by publisher]
Partial-correlation based retinotopically organized resting-state functional connectivity within and between areas of the visual cortex reflects more than cortical distance.
Brain Connect. 2015 Sep 28;
Authors: Dawson DA, Lam J, Lewis LB, Carbonell FM, Mendola JD, Shmuel A
Recent evidence suggests that BOLD-fMRI resting-state-functional-connectivity (RSFC) reflects functional organization at a sub visual-area scale. Here we investigated whether RSFCs within and between lower visual-areas are retinotopically organized, and whether retinotopically organized RSFC merely reflects cortical distance. Visual-areas V1, V2 and V3 were subdivided into regions of interest (ROIs) according to quadrants and visual-field eccentricity. RSFC was computed based on Pearson's linear-correlation and linear partial-correlation (correlation between two time-courses after the time-courses from all other regions in the network are regressed-out). Within a quadrant, within visual-areas, all correlation and partial-correlation measures showed statistical significance. Consistently in V1, V2, and to a lesser extent in V3, correlation decreased with increasing eccentricity separation. Consistent with previously reported monkey anatomical connectivity, correlation/partial-correlation values between regions from adjacent areas (V1-V2 and V2-V3) were higher than those between non-adjacent areas (V1-V3). Within a quadrant, partial-correlation showed consistent significance between regions from 2 different areas with the same or adjacent eccentricities. Pairs of ROIs with similar eccentricity showed higher correlation/partial-correlation than pairs of ROIs distant in eccentricity. Between dorsal and ventral quadrants, partial-correlation between common and adjacent eccentricity regions within a visual-area showed statistical significance. Within and between quadrants, correlation decreased approximately linearly with increasing distances separating the tested ROIs. Partial-correlation showed a more complex dependence on cortical distance: it decreased exponentially within quadrant, but fitted best a quadratic function between quadrants. We conclude that RSFCs within and between lower visual-areas are retinotopically organized. Correlation-based FC is non-selectively high across lower visual-areas, even between regions that do not share direct anatomical connections. The mechanisms likely involve network effects caused by the dense anatomical connectivity and projections from higher visual-areas. FC based on partial-correlation follows expectations based on direct anatomical connections in the monkey better than Corr does. Lastly, partial-correlation based retinotopically organized RSFC reflects more than cortical distance effects.
PMID: 26415043 [PubMed - as supplied by publisher]