29 results found
Li LM, Violante IR, Leech R, et al., 2019, Brain state and polarity dependent modulation of brain networks by transcranial direct current stimulation., Hum Brain Mapp, Vol: 40, Pages: 904-915
Despite its widespread use in cognitive studies, there is still limited understanding of whether and how transcranial direct current stimulation (tDCS) modulates brain network function. To clarify its physiological effects, we assessed brain network function using functional magnetic resonance imaging (fMRI) simultaneously acquired during tDCS stimulation. Cognitive state was manipulated by having subjects perform a Choice Reaction Task or being at "rest." A novel factorial design was used to assess the effects of brain state and polarity. Anodal and cathodal tDCS were applied to the right inferior frontal gyrus (rIFG), a region involved in controlling activity large-scale intrinsic connectivity networks during switches of cognitive state. tDCS produced widespread modulation of brain activity in a polarity and brain state dependent manner. In the absence of task, the main effect of tDCS was to accentuate default mode network (DMN) activation and salience network (SN) deactivation. In contrast, during task performance, tDCS increased SN activation. In the absence of task, the main effect of anodal tDCS was more pronounced, whereas cathodal tDCS had a greater effect during task performance. Cathodal tDCS also accentuated the within-DMN connectivity associated with task performance. There were minimal main effects of stimulation on network connectivity. These results demonstrate that rIFG tDCS can modulate the activity and functional connectivity of large-scale brain networks involved in cognitive function, in a brain state and polarity dependent manner. This study provides an important insight into mechanisms by which tDCS may modulate cognitive function, and also has implications for the design of future stimulation studies.
Li LM, Violante IR, Leech R, et al., 2019, Cognitive enhancement with Salience Network electrical stimulation is influenced by network structural connectivity, NEUROIMAGE, Vol: 185, Pages: 425-433, ISSN: 1053-8119
Carvalho Pereira A, Violante IR, Mouga S, et al., 2018, Medial Frontal Lobe Neurochemistry in Autism Spectrum Disorder is Marked by Reduced N-Acetylaspartate and Unchanged Gamma-Aminobutyric Acid and Glutamate + Glutamine Levels, Journal of Autism and Developmental Disorders, Vol: 48, Pages: 1467-1482, ISSN: 0162-3257
© 2017, Springer Science+Business Media, LLC, part of Springer Nature. The nature of neurochemical changes in autism spectrum disorder (ASD) remains controversial. We compared medial prefrontal cortex (mPFC) neurochemistry of twenty high-functioning children and adolescents with ASD without associated comorbidities and fourteen controls. We observed reduced total N-acetylaspartate (tNAA) and total creatine, increased Glx/tNAA but unchanged glutamate + glutamine (Glx) and unchanged absolute or relative gamma-aminobutyric acid (GABA+) in the ASD group. Importantly, both smaller absolute and relative GABA+ levels were associated with worse communication skills and developmental delay scores assessed by the autism diagnostic interview—revised (ADI-R). We conclude that tNAA is reduced in the mPFC in ASD and that glutamatergic metabolism may be altered due to unbalanced Glx/tNAA. Moreover, GABA+ is related to autistic symptoms assessed by the ADI-R.
Lorenz R, Violante IR, Monti RP, et al., 2018, Dissociating frontoparietal brain networks with neuroadaptive Bayesian optimization, NATURE COMMUNICATIONS, Vol: 9, ISSN: 2041-1723
, 2018, Oscillatory motor patterning is impaired in neurofibromatosis type 1: A behavioural, EEG and fMRI study, Journal of Neurodevelopmental Disorders, Vol: 10, ISSN: 1866-1947
© 2018 The Author(s). Background: Neurofibromatosis type1 (NF1) is associated with a broad range of behavioural deficits, and an imbalance between excitatory and inhibitory neurotransmission has been postulated in this disorder. Inhibition is involved in the control of frequency and stability of motor rhythms. Therefore, we aimed to explore the link between behavioural motor control, brain rhythms and brain activity, as assessed by EEG and fMRI in NF1. Methods: We studied a cohort of 21 participants with NF1 and 20 age- and gender-matched healthy controls, with a finger-tapping task requiring pacing at distinct frequencies during EEG and fMRI scans. Results: We found that task performance was significantly different between NF1 and controls, the latter showing higher tapping time precision. The time-frequency patterns at the beta sub-band (20-26 Hz) mirrored the behavioural modulations, with similar cyclic synchronization/desynchronization patterns for both groups. fMRI results showed a higher recruitment of the extrapyramidal motor system (putamen, cerebellum and red nucleus) in the control group during the fastest pacing condition. Conclusions: The present study demonstrated impaired precision in rhythmic pacing behaviour in NF1 as compared with controls. We found a decreased recruitment of the cerebellum, a structure where inhibitory interneurons are essential regulators of rhythmic synchronization, and in deep brain regions pivotally involved in motor pacing. Our findings shed light into the neural underpinnings of motor timing deficits in NF1.
Datta G, Violante IR, Scott G, et al., 2017, Translocator positron-emission tomography and magnetic resonance spectroscopic imaging of brain glial cell activation in multiple sclerosis, MULTIPLE SCLEROSIS JOURNAL, Vol: 23, Pages: 1469-1478, ISSN: 1352-4585
Sliwinska MW, Violante IR, Wise RJS, et al., 2017, Stimulating Multiple-Demand Cortex Enhances Vocabulary Learning, JOURNAL OF NEUROSCIENCE, Vol: 37, Pages: 7606-7618, ISSN: 0270-6474
Lorenz R, Violante I, Monti RP, et al., 2017, Dissociating frontoparietal brain networks with neuroadaptive Bayesian optimization
Understanding the unique contributions of frontoparietal networks (FPN) in cognition is challenging because different FPNs spatially overlap and are co-activated for diverse tasks. In order to characterize these networks involves studying how they activate across many different cognitive tasks, which has only previously been possible with meta-analyses. Here, building upon meta-analyses as a starting point, we use neuroadaptive Bayesian optimization, an approach combining real-time analysis of functional neuroimaging data with machine-learning, to discover cognitive tasks that dissociate ventral and dorsal FPN activity from a large pool of tasks. We identify and subsequently refine two cognitive tasks (Deductive Reasoning and Tower of London) that are optimal for dissociating the FPNs. The identified cognitive tasks are not those predicted by meta-analysis, highlighting a different mapping between cognitive tasks and frontoparietal networks than expected. The optimization approach converged on a similar neural dissociation independently for the two different tasks, suggesting a possible common underlying functional mechanism and the need for neurally-derived cognitive taxonomies.
Violante IR, Li LM, Carmichael DW, et al., 2017, Externally induced frontoparietal synchronization modulates network dynamics and enhances working memory performance, ELIFE, Vol: 6, ISSN: 2050-084X
Violante IR, Li LM, Carmichael DW, et al., 2017, Externally induced frontoparietal synchronization modulates network dynamics and enhances working memory performance., Elife, Vol: 6
Cognitive functions such as working memory (WM) are emergent properties of large-scale network interactions. Synchronisation of oscillatory activity might contribute to WM by enabling the coordination of long-range processes. However, causal evidence for the way oscillatory activity shapes network dynamics and behavior in humans is limited. Here we applied transcranial alternating current stimulation (tACS) to exogenously modulate oscillatory activity in a right frontoparietal network that supports WM. Externally induced synchronization improved performance when cognitive demands were high. Simultaneously collected fMRI data reveals tACS effects dependent on the relative phase of the stimulation and the internal cognitive processing state. Specifically, synchronous tACS during the verbal WM task increased parietal activity, which correlated with behavioral performance. Furthermore, functional connectivity results indicate that the relative phase of frontoparietal stimulation influences information flow within the WM network. Overall, our findings demonstrate a link between behavioral performance in a demanding WM task and large-scale brain synchronization.
Gonçalves J, Violante IR, Sereno J, et al., 2017, Testing the excitation/inhibition imbalance hypothesis in a mouse model of the autism spectrum disorder: in vivo neurospectroscopy and molecular evidence for regional phenotypes., Mol Autism, Vol: 8
BACKGROUND: Excitation/inhibition (E/I) imbalance remains a widely discussed hypothesis in autism spectrum disorders (ASD). The presence of such an imbalance may potentially define a therapeutic target for the treatment of cognitive disabilities related to this pathology. Consequently, the study of monogenic disorders related to autism, such as neurofibromatosis type 1 (NF1), represents a promising approach to isolate mechanisms underlying ASD-related cognitive disabilities. However, the NF1 mouse model showed increased γ-aminobutyric acid (GABA) neurotransmission, whereas the human disease showed reduced cortical GABA levels. It is therefore important to clarify whether the E/I imbalance hypothesis holds true. We hypothesize that E/I may depend on distinct pre- and postsynaptic push-pull mechanisms that might be are region-dependent. METHODS: In current study, we assessed two critical components of E/I regulation: the concentration of neurotransmitters and levels of GABA(A) receptors. Measurements were performed across the hippocampi, striatum, and prefrontal cortices by combined in vivo magnetic resonance spectroscopy (MRS) and molecular approaches in this ASD-related animal model, the Nf1+/- mouse. RESULTS: Cortical and striatal GABA/glutamate ratios were increased. At the postsynaptic level, very high receptor GABA(A) receptor expression was found in hippocampus, disproportionately to the small reduction in GABA levels. Gabaergic tone (either by receptor levels change or GABA/glutamate ratios) seemed therefore to be enhanced in all regions, although by a different mechanism. CONCLUSIONS: Our data provides support for the hypothesis of E/I imbalance in NF1 while showing that pre- and postsynaptic changes are region-specific. All these findings are consistent with our previous physiological evidence of increased inhibitory tone. Such heterogeneity suggests that therapeutic approaches to address neurochemical imbalance in ASD may need to focus on targets wher
Ribeiro Violante I, Patricio M, Bernardino I, et al., 2016, GABA deficiency in NF1: a multimodal [11C]-Flumazenil and spectroscopy study, Neurology, ISSN: 0028-3878
Objective: To provide a comprehensive investigation of the GABA system inpatients with Neurofibromatosis type 1 (NF1) that allows understanding thenature of the GABA imbalance in humans at pre- and post-synaptic levels.Methods: In this cross-sectional study, we employed multimodal imaging andspectroscopy measures to investigate GABAA receptor binding, using [11C]-Flumazenil positron emission tomography (PET), and GABA concentration,using magnetic resonance spectroscopy (MRS). 14 adult patients with NF1 and13 matched controls were included in the study. MRS was performed in theoccipital cortex and in a frontal region centered in the functionally localizedfrontal-eye fields. PET and MRS acquisitions were performed in the same day.Results: Patients with NF1 have reduced concentration of GABA+ in theoccipital cortex (P = 0.004) and frontal-eye fields (P = 0.026). PET resultsshowed decreased binding of GABAA receptors in patients in the parietooccipitalcortex, midbrain and thalamus, which are not explained by decreasedgrey matter levels.Conclusions: Abnormalities in the GABA system in NF1 involve both GABAconcentration and GABAA receptor density suggestive of neurodevelopmentalsynaptopathy with both pre- and post-synaptic involvement.
Lorenz R, Monti RP, Violante IR, et al., 2016, The Automatic Neuroscientist: A framework for optimizing experimental design with closed-loop real-time fMRI, NEUROIMAGE, Vol: 129, Pages: 320-334, ISSN: 1053-8119
Silva G, Ribeiro MJ, Costa GN, et al., 2016, Peripheral Attentional Targets under Covert Attention Lead to Paradoxically Enhanced Alpha Desynchronization in Neurofibromatosis Type 1, PLOS ONE, Vol: 11, ISSN: 1932-6203
Lorenz R, Monti RP, Hampshire A, et al., 2016, Towards tailoring non-invasive brain stimulation using real-time fMRI and Bayesian optimization, 6th International Workshop on Pattern Recognition in Neuroimaging (PRNI), Publisher: IEEE, Pages: 49-52, ISSN: 2330-9989
Ribeiro MJ, Violante IR, Bernardino I, et al., 2015, Abnormal relationship between GABA, neurophysiology and impulsive behavior in neurofibromatosis type 1, CORTEX, Vol: 64, Pages: 194-208, ISSN: 0010-9452
Majewska P, Ribeiro Violante I, Lorenz R, et al., 2015, EEG characteristics of memory deficits in acute traumatic brain injury patients with post-traumatic amnesia, The Society of British Neurological Surgeons Meeting 2015
Mullins PG, McGonigle DJ, O'Gorman RL, et al., 2014, Current practice in the use of MEGA-PRESS spectroscopy for the detection of GABA, NEUROIMAGE, Vol: 86, Pages: 43-52, ISSN: 1053-8119
Duarte JV, Ribeiro MJ, Violante IR, et al., 2014, Multivariate Pattern Analysis Reveals Subtle Brain Anomalies Relevant to the Cognitive Phenotype in Neurofibromatosis Type 1, HUMAN BRAIN MAPPING, Vol: 35, Pages: 89-106, ISSN: 1065-9471
Lorenz R, Faisal AA, Dinov M, et al., 2014, Neurofeedback training of large-scale brain networks, Annual Meeting of Society of Neuroscience
Violante IR, Ribeiro MJ, Edden RAE, et al., 2013, GABA deficit in the visual cortex of patients with neurofibromatosis type 1: genotype-phenotype correlations and functional impact, BRAIN, Vol: 136, Pages: 918-925, ISSN: 0006-8950
Violante IR, Ribeiro MJ, Silva ED, et al., 2013, Gyrification, cortical and subcortical morphometry in neurofibromatosis type 1: an uneven profile of developmental abnormalities, JOURNAL OF NEURODEVELOPMENTAL DISORDERS, Vol: 5, ISSN: 1866-1947
Violante IR, Ribeiro MJ, Cunha G, et al., 2012, Abnormal Brain Activation in Neurofibromatosis Type 1: A Link between Visual Processing and the Default Mode Network, PLOS ONE, Vol: 7, ISSN: 1932-6203
Ribeiro MJ, Violante IR, Bernardino I, et al., 2012, Abnormal Achromatic and Chromatic Contrast Sensitivity in Neurofibromatosis Type 1, INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE, Vol: 53, Pages: 287-293, ISSN: 0146-0404
Delgado TC, Violante IR, Nieto-Charques L, et al., 2011, Neuroglial metabolic compartmentation underlying leptin deficiency in the obese ob/ob mice as detected by magnetic resonance imaging and spectroscopy methods, JOURNAL OF CEREBRAL BLOOD FLOW AND METABOLISM, Vol: 31, Pages: 2257-2266, ISSN: 0271-678X
Neurofibromatosis type 1 (NF1) is a genetic disorder characterized by increased predisposition for tumor development and cognitive deficits. In this work, we used maps of grey matter density obtained from Magnetic Resonance (MR) brain structural scans to distinguish between NF1 patients and healthy controls with a multivariate pattern analysis technique, Support Vector Machines. Up to 83% of all participants were correctly classified (mean sensitivity of 82%; mean specificity of 84%; significance level p< 0.01). This high level of classification accuracy of NF1 patients suggests this technique as a potential diagnostic tool. In addition, we determined the brain regions that the algorithm used to distinguish between NF1 patients and healthy controls. These regions were not identified as abnormal using univariate voxel-by-voxel comparison indicating that multivariate techniques are a useful powerful tool with which to identify potential structural defects in the NF1 brain. © 2011 IEEE.
Rodrigues TB, Violante IR, Cerdan S, 2010, Unambiguous Assignment of the H3S and H3R Deuterations of Cerebral (2-C-13) Glutamate by C-13 NMR at 18.8 Tesla, MAGNETIC RESONANCE IN MEDICINE, Vol: 63, Pages: 1088-1091, ISSN: 0740-3194
Violante IR, Anastasovska J, Sanchez-Canon GJ, et al., 2009, Cerebral Activation by Fasting Induces Lactate Accumulation in the Hypothalamus, MAGNETIC RESONANCE IN MEDICINE, Vol: 62, Pages: 279-283, ISSN: 0740-3194
Ramirez BG, Rodrigues TB, Violante IR, et al., 2007, Kinetic properties of the redox switch/redox coupling mechanism as determined in primary cultures of cortical neurons and astrocytes from rat brain, JOURNAL OF NEUROSCIENCE RESEARCH, Vol: 85, Pages: 3244-3253, ISSN: 0360-4012
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