34 results found
Hampshire A, Daws RE, Neves ID, et al., 2019, Probing cortical and sub-cortical contributions to instruction-based learning: Regional specialisation and global network dynamics., Neuroimage, Vol: 192, Pages: 88-100
Diverse cortical networks and striatal brain regions are implicated in instruction-based learning (IBL); however, their distinct contributions remain unclear. We use a modified fMRI paradigm to test two hypotheses regarding the brain mechanisms that underlie IBL. One hypothesis proposes that anterior caudate and frontoparietal regions transiently co-activate when new rules are being bound in working memory. The other proposes that they mediate the application of the rules at different stages of the consolidation process. In accordance with the former hypothesis, we report strong activation peaks within and increased connectivity between anterior caudate and frontoparietal regions when rule-instruction slides are presented. However, similar effects occur throughout a broader set of cortical and sub-cortical regions, indicating a metabolically costly reconfiguration of the global brain state. The distinct functional roles of cingulo-opercular, frontoparietal and default-mode networks are apparent from their activation throughout, early and late in the practice phase respectively. Furthermore, there is tentative evidence of a peak in anterior caudate activity mid-way through the practice stage. These results demonstrate how performance of the same simple task involves a steadily shifting balance of brain systems as learning progresses. They also highlight the importance of distinguishing between regional specialisation and global dynamics when studying the network mechanisms that underlie cognition and learning.
Li LM, Violante IR, Leech R, et al., 2019, Brain state and polarity dependent modulation of brain networks by transcranial direct current stimulation, HUMAN BRAIN MAPPING, Vol: 40, Pages: 904-915, ISSN: 1065-9471
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
d'Almeida OC, Violante IR, Quendera B, et al., 2018, Mitochondrial pathophysiology beyond the retinal ganglion cell: occipital GABA is decreased in autosomal dominant optic neuropathy, GRAEFES ARCHIVE FOR CLINICAL AND EXPERIMENTAL OPHTHALMOLOGY, Vol: 256, Pages: 2341-2348, ISSN: 0721-832X
Pereira AC, 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 plus Glutamine Levels, JOURNAL OF AUTISM AND DEVELOPMENTAL DISORDERS, Vol: 48, Pages: 1467-1482, ISSN: 0162-3257
Lorenz R, Violante IR, Monti RP, et al., 2018, Dissociating frontoparietal brain networks with neuroadaptive Bayesian optimization, NATURE COMMUNICATIONS, Vol: 9, ISSN: 2041-1723
Silva G, Duarte IC, Bernardino I, et al., 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
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
Goncalves 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, MOLECULAR AUTISM, Vol: 8, ISSN: 2040-2392
Li L, Violante I, Leech R, et al., 2017, Brain state and polarity dependent modulation of brain networks by transcranial direct current stimulation
Transcranial direct current stimulation (TDCS) has been widely used to improve cognitive function. However, current deficiencies in mechanistic understanding hinders wider applicability. To clarify its physiological effects, we acquired fMRI whilst simultaneously acquiring TDCS to the right inferior frontal gyrus (rIFG) of healthy human participants, a region involved in coordinating activity within brain networks. TDCS caused widespread modulation of network activity depending on brain state ('rest' or choice reaction time task) and polarity (anodal or cathodal). During task, TDCS increased salience network activation and default mode network deactivation, but had the opposite effect during 'rest'. Furthermore, there was an interaction between brain state and TDCS polarity, with cathodal effects more pronounced during task performance and anodal effects more pronounced during 'rest'. Overall, we show that rIFG TDCS produces brain state and polarity dependent effects within large-scale cognitive networks, in a manner that goes beyond predictions from the current literature.
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, Simmons L, Monti R, et al., 2017, Assessing tACS-induced phosphene perception using closed-loop Bayesian optimization
Transcranial alternating current stimulation (tACS) can evoke illusory flash-like visual percepts known as phosphenes . The perception of phosphenes represents a major experimental challenge when studying tACS-induced effects on cognitive performance. Besides growing concerns that retinal phosphenes themselves could potentially have neuromodulatory effects, the perception of phosphenes may also modify the alertness of participants. Past research has shown that stimulation intensity, frequency and electrode montage affect phosphene perception. However, to date, the effect of an additional tACS parameter on phosphene perception has been completely overlooked: the relative phase difference between stimulation electrodes. This is a crucial and timely topic given the confounding nature of phosphene perception and the increasing number of studies reporting changes in cognitive function following tACS phase manipulations. However, studying phosphene perception for different frequencies and phases simultaneously is not tractable using standard approaches, as the physiologically plausible range of parameters results in a combinatorial explosion of experimental conditions, yielding impracticable experiment durations. To overcome this limitation, here we applied a Bayesian optimization approach to efficiently sample an exhaustive tACS parameter space. Moreover, unlike conventional methodology, which involves subjects judging the perceived phosphene intensity on a rating scale, our study leveraged the strength of human perception by having the optimization driven based on a subject's relative judgement. Applying Bayesian optimization for two different montages, we found that phosphene perception was affected by differences in the relative phase between cortical electrodes. The results were replicated in a second study involving new participants and validated using computational modelling. In summary, our results have important implications for the experimental design and concl
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.
Violante IR, Patricio M, Bernardino I, et al., 2016, GABA deficiency in NF1: A multimodal [11C]-flumazenil and spectroscopy study., Neurology, Vol: 87, Pages: 897-904
OBJECTIVE: To provide a comprehensive investigation of the γ-aminobutyric acid (GABA) system in patients with neurofibromatosis type 1 (NF1) that allows understanding the nature of the GABA imbalance in humans at pre- and postsynaptic levels. METHODS: In this cross-sectional study, we employed multimodal imaging and spectroscopy measures to investigate GABA type A (GABAA) receptor binding, using [(11)C]-flumazenil PET, and GABA concentration, using magnetic resonance spectroscopy (MRS). Fourteen adult patients with NF1 and 13 matched controls were included in the study. MRS was performed in the occipital cortex and in a frontal region centered in the functionally localized frontal eye fields. PET and MRS acquisitions were performed in the same day. RESULTS: Patients with NF1 have reduced concentration of GABA+ in the occipital cortex (p = 0.004) and frontal eye fields (p = 0.026). PET results showed decreased binding of GABAA receptors in patients in the parieto-occipital cortex, midbrain, and thalamus, which are not explained by decreased gray matter levels. CONCLUSIONS: Abnormalities in the GABA system in NF1 involve both GABA concentration and GABAA receptor density suggestive of neurodevelopmental synaptopathy with both pre- and postsynaptic involvement.
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
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