Hippocampal-parietal dysconnectivity and glutamate abnormalities in unmedicated patients with schizophrenia.
Hippocampus. 2014 Jul 17;
Authors: Kraguljac NV, White DM, Hadley J, Reid MA, Lahti AC
Objectives. Abnormalities in resting state connectivity in schizophrenia are now well established, but the biological substrates of these functional alterations remain to be elucidated. Experimental design. We performed a combined functional magnetic resonance imaging (fMRI) and magnetic resonance spectroscopy ((1) H-MRS) study in 22 unmedicated patients with schizophrenia and 22 matched healthy controls to evaluate resting state functional connectivity of the hippocampus and Glx/Cr (a combined glutamate+glutamine peak normalized to creatine) in the hippocampus and investigate functional and neurometabolic abnormalities and examine the relationship between these. Major observations. Functional connectivity between the left hippocampus and bilateral precuneus was significantly decreased in unmedicated patients with schizophrenia when compared to healthy controls [t(4.22), cluster extent (kE)= 751, pFDRcorr =.001, MNI coordinates: x= -4, y= -56, z= 44]. Glx/Cr in the hippocampus was significantly elevated in schizophrenia (HC: mean= 0.60+/- 0.10 SZ: 0.67+/- 0.10; F= 5.742; p=.02), but was not correlated with functional connectivity deficits (p >.05). Conclusions. In this study, we found hippocampal resting state functional connectivity deficits to the precuneus in unmedicated patients with schizophrenia and an increase of Glx/Cr in the hippocampus, but did not observe a direct relationship between these abnormalities. However, our findings do not exclude the possibility of a shared underlying pathology which warrants further investigation. © 2014 Wiley Periodicals, Inc.
PMID: 25045047 [PubMed - as supplied by publisher]
Isoflurane induces dose-dependent alterations in the cortical connectivity profiles and dynamic properties of the brain's functional architecture.
Hum Brain Mapp. 2014 Jul 12;
Authors: Hutchison RM, Hutchison M, Manning KY, Menon RS, Everling S
Despite their widespread use, the effect of anesthetic agents on the brain's functional architecture remains poorly understood. This is particularly true of alterations that occur beyond the point of induced unconsciousness. Here, we examined the distributed intrinsic connectivity of macaques across six isoflurane levels using resting-state functional MRI (fMRI) following the loss of consciousness. The results from multiple analysis strategies showed stable functional connectivity (FC) patterns between 1.00% and 1.50% suggesting this as a suitable range for anesthetized nonhuman primate resting-state investigations. Dose-dependent effects were evident at moderate to high dosages showing substantial alteration of the functional topology and a decrease or complete loss of interhemispheric cortical FC strength including that of contralateral homologues. The assessment of dynamic FC patterns revealed that the functional repertoire of brain states is related to anesthesia depth and most strikingly, that the number of state transitions linearly decreases with increased isoflurane dosage. Taken together, the results indicate dose-specific spatial and temporal alterations of FC that occur beyond the typically defined endpoint of consciousness. Future work will be necessary to determine how these findings generalize across anesthetic types and extend to the transition between consciousness and unconsciousness. Hum Brain Mapp, 2014. © 2014 Wiley Periodicals, Inc.
PMID: 25044934 [PubMed - as supplied by publisher]
Computer-automated focus lateralization of temporal lobe epilepsy using fMRI.
J Magn Reson Imaging. 2014 Jul 9;
Authors: Chiang S, Levin HS, Haneef Z
PURPOSE: To compare the performance of computer-automated diagnosis using functional magnetic resonance imaging (fMRI) interictal graph theory (CADFIG) to that achieved in standard clinical practice with MRI, for lateralizing the affected hemisphere in temporal lobe epilepsy (TLE).
MATERIALS AND METHODS: Interictal resting state fMRI and high-resolution MRI were performed on 14 left and 10 right TLE patients. Functional topology measures were calculated from fMRI using graph theory, and used to lateralize the epileptogenic hemisphere using quadratic discriminant analysis. Leave-one-out cross-validation prediction accuracy of CADFIG was compared to performance based on expert manual analysis (MA) of MRI, using video EEG as the "gold standard" for focus lateralization.
RESULTS: CADFIG correctly lateralized 95.8% (23/24) of cases, compared to 66.7% (16/24) with expert MA of MRI. Combining MA with CADFIG allowed all cases (24/24) to be correctly lateralized. CADFIG correctly identified the affected hemisphere for all patients (8/8) where MRI failed to lateralize.
CONCLUSION: CADFIG based on fMRI lateralized the affected hemisphere in TLE with superior performance compared to expert MA of MRI. These results demonstrate that functional patterns in fMRI can be used with automated machine learning for diagnostic lateralization in TLE. Addition of fMRI-based tests to existing protocols for identifying the affected hemisphere in presurgical assessment can improve diagnostic accuracy and surgical outcome in TLE.J. Magn. Reson. Imaging 2014. © 2014 Wiley Periodicals, Inc.
PMID: 25044773 [PubMed - as supplied by publisher]
Decreased limbic and increased fronto-parietal connectivity in unmedicated patients with obsessive-compulsive disorder.
Hum Brain Mapp. 2014 Jul 12;
Authors: Göttlich M, Krämer UM, Kordon A, Hohagen F, Zurowski B
Obsessive-compulsive disorder (OCD) is characterized by recurrent intrusive thoughts and ritualized, repetitive behaviors, or mental acts. Convergent experimental evidence from neuroimaging and neuropsychological studies supports an orbitofronto-striato-thalamo-cortical dysfunction in OCD. Moreover, an over excitability of the amygdala and over monitoring of thoughts and actions involving the anterior cingulate, frontal and parietal cortex has been proposed as aspects of pathophysiology in OCD. We chose a data driven, graph theoretical approach to investigate brain network organization in 17 unmedicated OCD patients and 19 controls using resting-state fMRI. OCD patients showed a decreased connectivity of the limbic network to several other brain networks: the basal ganglia network, the default mode network, and the executive/attention network. The connectivity within the limbic network was also found to be decreased in OCD patients compared to healthy controls. Furthermore, we found a stronger connectivity of brain regions within the executive/attention network in OCD patients. This effect was positively correlated with disease severity. The decreased connectivity of limbic regions (amygdala, hippocampus) may be related to several neurocognitive deficits observed in OCD patients involving implicit learning, emotion processing and expectation, and processing of reward and punishment. Limbic disconnection from fronto-parietal regions relevant for (re)-appraisal may explain why intrusive thoughts become and/or remain threatening to patients but not to healthy subjects. Hyperconnectivity within the executive/attention network might be related to OCD symptoms such as excessive monitoring of thoughts and behavior as a dysfunctional strategy to cope with threat and uncertainty. Hum Brain Mapp, 2014. © 2014 Wiley Periodicals, Inc.
PMID: 25044747 [PubMed - as supplied by publisher]
Role of the sensorimotor cortex in tourette syndrome using multimodal imaging.
Hum Brain Mapp. 2014 Jul 15;
Authors: Tinaz S, Belluscio BA, Malone P, van der Veen JW, Hallett M, Horovitz SG
Tourette syndrome (TS) is a neuropsychiatric disorder characterized by motor and vocal tics. Most patients describe uncomfortable premonitory sensations preceding the tics and a subjective experience of increased sensitivity to tactile stimuli. These reports indicate that a sensory processing disturbance is an important component of TS together with motor phenomena. Thus, we focused our investigation on the role of the sensorimotor cortex (SMC) in TS using multimodal neuroimaging techniques. We measured the gamma-aminobutyric acid (GABA)+/Creatine (Cre) ratio in the SMC using GABA (1) H magnetic resonance spectroscopy. We recorded the baseline beta activity in the SMC using magnetoencephalography and correlated GABA+/Cre ratio with baseline beta band power. Finally, we examined the resting state functional connectivity (FC) pattern of the SMC using functional magnetic resonance imaging (fMRI). GABA+/Cre ratio in the SMC did not differ between patients and controls. Correlation between the baseline beta band power and GABA+/Cre ratio was abnormal in patients. The anterior insula showed increased FC with the SMC in patients. These findings suggest that altered limbic input to the SMC and abnormal GABA-mediated beta oscillations in the SMC may underpin some of the sensorimotor processing disturbances in TS and contribute to tic generation. Hum Brain Mapp, 2014. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.
PMID: 25044024 [PubMed - as supplied by publisher]
Link between hippocampus' raised local and eased global intrinsic connectivity in AD.
Alzheimers Dement. 2014 Jul 17;
Authors: Pasquini L, Scherr M, Tahmasian M, Meng C, Myers NE, Ortner M, Mühlau M, Kurz A, Förstl H, Zimmer C, Grimmer T, Wohlschläger AM, Riedl V, Sorg C
BACKGROUND: The hippocampus (HP) is part of the default mode network (DMN), and both are key targets of Alzheimer's disease (AD). Because of widespread network degeneration, it has been suggested that increasing HP disconnection from the DMN may lead to progressive disinhibition of intra-HP synchronized activity.
METHODS: To analyze HP local (i.e., within HP) and global (i.e., within DMN) intrinsic functional connectivity (local/global intrinsic functional connectivity [iFC]), healthy controls and patients with mild cognitive impairment and AD dementia were assessed by spatial high and normal resolution resting-state functional magnetic resonance imaging.
RESULTS: Although patients' parietal local-iFC was reduced and positively correlated with reduced global-iFC within the DMN, HP local connectivity was progressively increased and negatively correlated with HP decreased global connectivity. Increased intra-HP connectivity was associated with impaired memory.
CONCLUSION: Our result demonstrates a link between increased local and reduced global hippocampal connectivity in AD. Increased intra-HP synchrony may contribute to distinct symptoms such as memory impairment or more speculatively epileptic seizure.
PMID: 25043909 [PubMed - as supplied by publisher]
Increased interhemispheric resting-state in idiopathic generalized epilepsy with generalized tonic-clonic seizures: A resting-state fMRI study.
Epilepsy Res. 2014 Jul 7;
Authors: Yang T, Ren J, Li Q, Li L, Lei D, Gong Q, Zhou D
PURPOSE: The aim is to examine the resting state functional connectivity (RSFC) between the two hemispheres and its relationships with clinical characteristic in idiopathic generalized epilepsy with generalized tonic-clonic seizures only (IGE-GTCS) patients using a technique called "voxel-mirrored homotopic connectivity (VMHC)".
METHODS: The resting-state functional MRI (Rs-fMRI) was used to measure the RSFC in patients with IGE-GTC and age-gender matched healthy subjects. The between-group difference in interhemispheric RSFC was examined after the interhemispheric RSFC map was obtained by an automated VMHC approach.
RESULTS: Compared to the controls, the IGE-GTCS patients showed significant increases in VMHC in the bilateral anterior cingulate and medial prefrontal gyrus. No areas showed decreased VMHC in patients. Moreover, the VMHC in bilateral thalamus, orbital frontal cortex as well as cerebellum showed significant negative correlations with the illness duration.
CONCLUSIONS: The current findings provide preliminary evidence of increased interhemispheric RSFC in patients with IGE-GTCS during the interictal period. These VMHC deficits in these regions and the inverse relations between VMHC and clinical characteristic may play an important role in the pathophysiology of IGE-GTCS. Our study may contribute to the understanding of neuro-pathophysiological mechanism of epilepsy and psychosocial function impairments in patients with IGE-GTCS.
PMID: 25043752 [PubMed - as supplied by publisher]
Disrupted small world networks in patients without overt hepatic encephalopathy: A resting state fMRI study.
Eur J Radiol. 2014 Jul 2;
Authors: Zhang LJ, Zheng G, Zhang L, Zhong J, Li Q, Zhao TZ, Lu GM
PURPOSE: To explore changes in functional connectivity and topological organization of brain functional networks in cirrhotic patients with minimal hepatic encephalopathy (MHE) and non hepatic encephalopathy (nonHE) and their relationship with clinical markers.
MATERIALS AND METHODS: Resting-state functional MR imaging was acquired in 22 MHE, 29 nonHE patients and 33 healthy controls. Functional connectivity networks were obtained by computing temporal correlations between any pairs of 90 cortical and subcortical regions. Graph analysis measures were quantitatively assessed for each subject. One-way analysis of covariance was applied to identify statistical differences of functional connectivity and network parameters among three groups. Correlations between clinical markers, such as Child-Pugh scores, venous blood ammonia level, and number connection test type A (NCT-A)/digit symbol test (DST) scores, and connectivity/graph metrics were calculated.
RESULTS: Thirty functional connectivities represented by edges were found to be abnormal (P<0.05, FDR corrected) in cirrhotic patients, in which 16 edges (53.3%) were related with sub-cortical regions. MHE patients showed abnormal small-world attributes in the functional connectivity networks. Cirrhotic patients had significantly reduced nodal degree in 8 cortical regions and increased nodal centrality in 3 cortical regions. Twenty edges were correlated with either NCT-A or DST scores, in which 13 edges were related with sub-cortical regions. No correlation was found between Child-Pugh scores and graph theoretical measures in cirrhotic patients.
CONCLUSION: Disturbances of brain functional connectivity and small world property loss are associated with neurocognitive impairment of cirrhotic patients. Reorganization of brain network occurred during disease progression from nonHE to MHE.
PMID: 25043497 [PubMed - as supplied by publisher]
Posture alters human resting-state.
Cortex. 2014 Jun 28;58C:199-205
Authors: Thibault RT, Lifshitz M, Jones JM, Raz A
Neuroimaging is ubiquitous; however, neuroimagers seldom investigate the putative impact of posture on brain activity. Whereas participants in most psychological experiments sit upright, many prominent neuroimaging techniques (e.g., functional magnetic resonance imaging (fMRI)) require participants to lie supine. Such postural discrepancies may hold important implications for brain function in general and for fMRI in particular. We directly investigated the effect of posture on spontaneous brain dynamics by recording scalp electrical activity in four orthostatic conditions (lying supine, inclined at 45°, sitting upright, and standing erect). Here we show that upright versus supine posture increases widespread high-frequency oscillatory activity. Our electroencephalographic findings highlight the importance of posture as a determinant in neuroimaging. When generalizing supine imaging results to ecological human cognition, therefore, cognitive neuroscientists would benefit from considering the influence of posture on brain dynamics.
PMID: 25041937 [PubMed - as supplied by publisher]
[The impact of mood on the intrinsic functional connectivity].
Sheng Wu Yi Xue Gong Cheng Xue Za Zhi. 2014 Apr;31(2):262-6
Authors: Wang Z, Song S, Wang L
Although a great number of studies have investigated the changes of resting-state functional connectivity (rsFC) in patients with mental disorders, such as depression and schizophrenia etc, little is known how stable the changes are, and whether temporal sad or happy mood can modulate the intrinsic rsFC. In our experiments, happy and sad video clips were used to induce temporally happy and sad mood states in 20 healthy young adults. We collected functional magnetic resonance imaging (fMRI) data while participants were watching happy or sad video clips, which were administrated in two consecutive days. Seed-based functional connectivity analyses were conducted using the anterior cingulate cortex (ACC), dorsolateral prefrontal cortex (DLPFC), and amygdala as seeds to investigate neural network related to executive function, attention, and emotion. We also investigated the association of the rsFC changes with emotional arousability level to understand individual differences. There is significantly stronger functional connectivity between the left DLPFC and posterior cingulate cortex (PCC) under sad mood than that under happy mood. The increased connectivity strength was positively correlated with subjects' emotional arousability. The increased positive correlation between the left DLPFC and PCC under sad relative to happy mood might reflect an increased processing of negative emotion-relevant stimuli. The easier one was induced by strong negative emotion (higher emotional arousability), the greater the left DLPFC-PCC connectivity was indicated, the greater the instability of the intrinsic rsFC was shown.
PMID: 25039124 [PubMed - in process]
Impaired functional connectivity of brain reward circuitry in patients with schizophrenia and cannabis use disorder: Effects of cannabis and THC.
Schizophr Res. 2014 Jul 15;
Authors: Fischer AS, Whitfield-Gabrieli S, Roth RM, Brunette MF, Green AI
Cannabis use disorder (CUD) occurs in up to 42% of patients with schizophrenia and substantially worsens disease progression. The basis of CUD in schizophrenia is unclear and available treatments are rarely successful at limiting cannabis use. We have proposed that a dysregulated brain reward circuit (BRC) may underpin cannabis use in these patients. In the present pilot study, we used whole-brain seed-to-voxel resting state functional connectivity (rs-fc) to examine the BRC of patients with schizophrenia and CUD, and to explore the effects of smoked cannabis and orally administered delta-9-tetrahydrocannabinol (THC) on the BRC. 12 patients with schizophrenia and CUD and 12 control subjects each completed two fMRI resting scans, with patients administered either a 3.6% THC cannabis cigarette (n=6) or a 15mg THC capsule (n=6) prior to their second scan. Results revealed significantly reduced connectivity at baseline in patients relative to controls, with most pronounced hypoconnectivity found between the nucleus accumbens and prefrontal cortical BRC regions (i.e., anterior prefrontal cortex, orbitofrontal cortex, and anterior cingulate cortex). Both cannabis and THC administration increased connectivity between these regions, in direct correlation with increases in plasma THC levels. This study is the first to investigate interregional connectivity of the BRC and the effects of cannabis and THC on this circuit in patients with schizophrenia and CUD. The findings from this pilot study support the use of rs-fc as a means of measuring the integrity of the BRC and the effects of pharmacologic agents acting on this circuit in patients with schizophrenia and CUD.
PMID: 25037524 [PubMed - as supplied by publisher]
Lewy body compared with Alzheimer dementia is associated with decreased functional connectivity in resting state networks.
Psychiatry Res. 2014 Jun 27;
Authors: Lowther ER, O'Brien JT, Firbank MJ, Blamire AM
Resting state functional magnetic resonance imaging (fMRI) was used to measure whole brain functional connectivity within specific networks hypothesised to be more affected in dementia with Lewy bodies (DLB) (a disease characterised by prominent attentional deficits, spontaneous motor features of parkinsonism and depression) than in Alzheimer׳s disease (AD) and controls. This study involved 68 subjects (15 DLB, 13 AD and 40 controls) who were scanned using resting state BOLD (blood-oxygen-level-dependent) fMRI on a 3T MRI scanner. Functional connectivity was measured using a model-free independent component analysis approach that consisted of temporally concatenating the resting state fMRI data of all study subjects and investigating group differences using a back-reconstruction procedure. Resting state functional connectivity was affected in the default mode, salience, executive and basal ganglia networks in DLB subjects compared with AD and controls. Functional connectivity was lower in DLB compared with AD and controls in these networks, except for the basal ganglia network, where connectivity was greater in DLB. No resting state networks showed less connectivity in AD compared with DLB or controls. Our results suggest that functional connectivity of resting state networks can identify differences between DLB and AD subjects that may help to explain why DLB subjects have more frequent attentional deficits, parkinsonian symptoms, and depression than those with AD.
PMID: 25035300 [PubMed - as supplied by publisher]
186 Spinal Cord Stimulation and Functional Magnetic Resonance Imaging: Pain Relief Correlates With Decreased Connectivity Between Somatosensory and Limbic Brain Networks.
Neurosurgery. 2014 Aug;61 Suppl 1:221-222
Authors: Deogaonkar M, Oluigbo C, Nielson D, Yang X, Sharma M, Vera-Portocarrero L, Molnar G, Abduljalil A, Sederberg P, Rezai AR
INTRODUCTION:: The aim of this study was to use resting state functional magnetic resonance imaging (rs-fMRI) to detect changes in cortical networks and cortical processing linked to pain relief from spinal cord stimulation.
METHODS:: Ten patients who have thoracic epidural spinal cord stimulators were enrolled in this Institutional Review Board approved study. Stimulation parameters associated with "optimal" pain reduction and SCS perception threshold were evaluated prior to imaging studies. rs-fMRI was obtained on a 3-Tesla, Philips Achieva MRI. The safety of MRI scanning with spinal cord stimulation (SCS) was determined previously. rsfMRI was performed with stimulator off (300 TRs), at sensory perception threshold (Low, 300 TRs) and at optimum (Opt, 300 TRs) therapeutic settings. Seed-based analysis of the resting state functional connectivity was conducted using seeds in regions linked to the pain networks or in the default mode network. NCUT parcellation was used to generate 100 cortical and subcortical regions of interest in order to expand analysis of changes in functional connections to the entire brain. We corrected for multiple comparisons by limiting the false discovery rate to 5%.
RESULTS:: There were no adverse effects with SCS and fMRI. Significant differences in resting state brain connectivity were seen between several regions related to pain perception, including the left frontal insula, right primary and secondary somatosensory cortices, as well as in regions involved in the default mode network (DMN). Therapeutic SCS resulted in decreased connection strength between somatosensory and limbic areas and increased connection strength between somatosensory and default mode network.
CONCLUSION:: fMRI can be safely performed with SCS. Pain relief from SCS reduces the connectivity between the somatosensory and limbic/affective regions as compared to baseline. This suggests that optimal spinal cord stimulation may be reducing negative emotional processing associated with pain, allowing somatosensory areas to become more integrated into default mode activity and normalization of brain networks.
PMID: 25032637 [PubMed - as supplied by publisher]
Coupling Mechanism and Significance of the BOLD Signal: A Status Report.
Annu Rev Neurosci. 2014 Jul 8;37:161-181
Authors: Hillman EM
Functional magnetic resonance imaging (fMRI) provides a unique view of the working human mind. The blood-oxygen-level-dependent (BOLD) signal, detected in fMRI, reflects changes in deoxyhemoglobin driven by localized changes in brain blood flow and blood oxygenation, which are coupled to underlying neuronal activity by a process termed neurovascular coupling. Over the past 10 years, a range of cellular mechanisms, including astrocytes, pericytes, and interneurons, have been proposed to play a role in functional neurovascular coupling. However, the field remains conflicted over the relative importance of each process, while key spatiotemporal features of BOLD response remain unexplained. Here, we review current candidate neurovascular coupling mechanisms and propose that previously overlooked involvement of the vascular endothelium may provide a more complete picture of how blood flow is controlled in the brain. We also explore the possibility and consequences of conditions in which neurovascular coupling may be altered, including during postnatal development, pathological states, and aging, noting relevance to both stimulus-evoked and resting-state fMRI studies.
PMID: 25032494 [PubMed - as supplied by publisher]
Shared and distinct intrinsic functional network centrality in autism and attention-deficit/hyperactivity disorder.
Biol Psychiatry. 2013 Oct 15;74(8):623-32
Authors: Di Martino A, Zuo XN, Kelly C, Grzadzinski R, Mennes M, Schvarcz A, Rodman J, Lord C, Castellanos FX, Milham MP
BACKGROUND: Individuals with autism spectrum disorders (ASD) often exhibit symptoms of attention-deficit/hyperactivity disorder (ADHD). Across both disorders, observations of distributed functional abnormalities suggest aberrant large-scale brain network connectivity. Yet, common and distinct network correlates of ASD and ADHD remain unidentified. Here, we aimed to examine patterns of dysconnection in school-age children with ASD and ADHD and typically developing children who completed a resting state functional magnetic resonance imaging scan.
METHODS: We measured voxelwise network centrality, functional connectivity metrics indexing local (degree centrality [DC]) and global (eigenvector centrality) functional relationships across the entire brain connectome, in resting state functional magnetic resonance imaging data from 56 children with ASD, 45 children with ADHD, and 50 typically developing children. A one-way analysis of covariance, with group as fixed factor (whole-brain corrected), was followed by post hoc pairwise comparisons.
RESULTS: Cortical and subcortical areas exhibited centrality abnormalities, some common to both ADHD and ASD, such as in precuneus. Others were disorder-specific and included ADHD-related increases in DC in right striatum/pallidum, in contrast with ASD-related increases in bilateral temporolimbic areas. Secondary analyses differentiating children with ASD into those with or without ADHD-like comorbidity (ASD(+) and ASD(-), respectively) revealed that the ASD(+) group shared ADHD-specific abnormalities in basal ganglia. By contrast, centrality increases in temporolimbic areas characterized children with ASD regardless of ADHD-like comorbidity. At the cluster level, eigenvector centrality group patterns were similar to DC.
CONCLUSIONS: ADHD and ASD are neurodevelopmental disorders with distinct and overlapping clinical presentations. This work provides evidence for both shared and distinct underlying mechanisms at the large-scale network level.
PMID: 23541632 [PubMed - indexed for MEDLINE]
Fast computation of voxel-level brain connectivity maps from resting-state functional MRI using l1-norm as approximation of Pearson's temporal correlation: Proof-of-concept and example vector hardware implementation.
Med Eng Phys. 2014 Jul 8;
Authors: Minati L, Zacà D, D'Incerti L, Jovicich J
An outstanding issue in graph-based analysis of resting-state functional MRI is choice of network nodes. Individual consideration of entire brain voxels may represent a less biased approach than parcellating the cortex according to pre-determined atlases, but entails establishing connectedness for 1(9)-1(11) links, with often prohibitive computational cost. Using a representative Human Connectome Project dataset, we show that, following appropriate time-series normalization, it may be possible to accelerate connectivity determination replacing Pearson correlation with l1-norm. Even though the adjacency matrices derived from correlation coefficients and l1-norms are not identical, their similarity is high. Further, we describe and provide in full an example vector hardware implementation of l1-norm on an array of 4096 zero instruction-set processors. Calculation times <1000s are attainable, removing the major deterrent to voxel-based resting-sate network mapping and revealing fine-grained node degree heterogeneity. L1-norm should be given consideration as a substitute for correlation in very high-density resting-state functional connectivity analyses.
PMID: 25023958 [PubMed - as supplied by publisher]
5.8 clinical and genetic influences on functional brain networks in preterm infants.
Arch Dis Child Fetal Neonatal Ed. 2014 Jun;99 Suppl 1:A6
Authors: Smith-Collins A, Heep A, Kauppinen R, Váradi A, Rajatileka S, Molnar E, Luyt K
: Preterm birth is associated with adverse neurodevelopmental outcomes. The pathological mechanisms leading to adverse outcomes involve several pathways, which are not fully understood. Current methods of assessing neurological injury associated with preterm birth have limited scope and low prognostic value. Whilst structural MRI may provide detailed anatomical information about the neonatal brain, there is imperfect mapping between structure and function. A supplementary approach is the use of functional MRI (fMRI) to infer functional connectivity (FC), evaluating integration of neural activity within the brain. There is emerging evidence that children who were born preterm show long term changes in FC, and early detection of such changes offers potential to improve understanding of pathophysiology of preterm brain injury. These functional changes may be influenced by both neonatal course and underlying susceptibilities to abnormal development, including genetic risk factors. We used resting state fMRI (rs-fMRI) at 3T to examine functional brain connectivity in 20 infants born at <32 weeks of gestation, scanned at term. Infants also had genetic testing to examine polymorphisms in the EAAT2 glutamate transporter, previously associated with variation in preterm neurodevelopmental outcomes. Using a multivariate model to examine the independent contributions of demographic, genetic and clinical characteristics of the infants to FC, we identified multiple dissociable influences on functional brain networks. This is the first report of genetic variability in cerebral glutamate homeostasis influencing neonatal brain connectivity. We discuss the impact on understanding preterm brain injury, and the potential for predicting neurodevelopmental outcome by non-invasive measurement of functional brain connectivity.
PMID: 25021297 [PubMed - in process]
Preserving subject variability in group fMRI analysis: performance evaluation of GICA vs. IVA.
Front Syst Neurosci. 2014;8:106
Authors: Michael AM, Anderson M, Miller RL, Adalı T, Calhoun VD
Independent component analysis (ICA) is a widely applied technique to derive functionally connected brain networks from fMRI data. Group ICA (GICA) and Independent Vector Analysis (IVA) are extensions of ICA that enable users to perform group fMRI analyses; however a full comparison of the performance limits of GICA and IVA has not been investigated. Recent interest in resting state fMRI data with potentially higher degree of subject variability makes the evaluation of the above techniques important. In this paper we compare component estimation accuracies of GICA and an improved version of IVA using simulated fMRI datasets. We systematically change the degree of inter-subject spatial variability of components and evaluate estimation accuracy over all spatial maps (SMs) and time courses (TCs) of the decomposition. Our results indicate the following: (1) at low levels of SM variability or when just one SM is varied, both GICA and IVA perform well, (2) at higher levels of SM variability or when more than one SMs are varied, IVA continues to perform well but GICA yields SM estimates that are composites of other SMs with errors in TCs, (3) both GICA and IVA remove spatial correlations of overlapping SMs and introduce artificial correlations in their TCs, (4) if number of SMs is over estimated, IVA continues to perform well but GICA introduces artifacts in the varying and extra SMs with artificial correlations in the TCs of extra components, and (5) in the absence or presence of SMs unique to one subject, GICA produces errors in TCs and IVA estimates are accurate. In summary, our simulation experiments (both simplistic and realistic) and our holistic analyses approach indicate that IVA produces results that are closer to ground truth and thereby better preserves subject variability. The improved version of IVA is now packaged into the GIFT toolbox (http://mialab.mrn.org/software/gift).
PMID: 25018704 [PubMed]
Functional plasticity before the cradle: a review of neural functional imaging in the human fetus.
Neurosci Biobehav Rev. 2013 Nov;37(9 Pt B):2220-32
Authors: Anderson AL, Thomason ME
The organization of the brain is highly plastic in fetal life. Establishment of healthy neural functional systems during the fetal period is essential to normal growth and development. Across the last several decades, remarkable progress has been made in understanding the development of human fetal functional brain systems. This is largely due to advances in imaging methodologies. Fetal neuroimaging began in the 1950-1970's with fetal electroencephalography (EEG) applied during labor. Later, in the 1980's, magnetoencephalography (MEG) emerged as an effective approach for investigating fetal brain function. Most recently, functional magnetic resonance imaging (fMRI) has arisen as an additional powerful approach for examining fetal brain function. This review will discuss major developmental findings from fetal imaging studies such as the maturation of prenatal sensory system functions, functional hemispheric asymmetry, and sensory-driven neurodevelopment. We describe how with improved imaging and analysis techniques, functional imaging of the fetus has the potential to assess the earliest point of neural maturation and provide insight into the patterning and sequence of normal and abnormal brain development.
PMID: 23542738 [PubMed - indexed for MEDLINE]
Motor Imagery Learning Induced Changes in Functional Connectivity of the Default Mode Network.
IEEE Trans Neural Syst Rehabil Eng. 2014 Jul 8;
Authors: Ge R, Zhang H, Yao L, Long Z
Numerous studies provide evidences that motor skill learning changes the activity of some brain regions during task as well as some resting networks during rest. However, it is still unclear how motor learning affects the resting-state default-mode network (DMN). Using functional magnetic resonance imaging (fMRI), this study investigated the alteration of the DMN after motor skill learning with mental imagery practice. 14 participants in the experimental group learned to imagine a sequential finger movement over a 2-week period while 12 control participants did not undergo motor imagery learning. For the experimental group, interregional connectivity, estimated by the graph theory method, between the medial temporal lobe, lateral temporal, and lateral parietal cortex within the DMN was increased after learning, whereas activity of the DMN network, estimated by the independent component analysis (ICA) method, remained stable. Moreover, the experimental group showed significant improvement in motor performance after learning and a negative correlation between the alteration of the execution rate and changes in activity in the lateral parietal cortex. These results indicate that the DMN could be sculpted by motor learning in a manner of altering interregional connectivity and may imply that the DMN plays a role in improving behavioral performance.
PMID: 25014958 [PubMed - as supplied by publisher]