Imagerie par résonance magnétique fonctionnelle

Résumé

thumb|Détection par l'IRMf de l'activation des régions du cerveau impliquées dans la perception visuelle. L’imagerie par résonance magnétique fonctionnelle (IRMf) est une application de l' permettant de visualiser, de manière indirecte, l'activité cérébrale. Il s'agit d'une technique d'imagerie utilisée pour l'étude du fonctionnement du cerveau. Elle consiste à enregistrer des variations hémodynamiques (variation des propriétés du flux sanguin) cérébrales locales minimes, lorsque ces zones sont stimulées. La localisation des zones cérébrales activées est basée sur l'effet BOLD (Blood Oxygen Level Dependant), lié à l’aimantation de l’hémoglobine contenue dans les globules rouges du sang. Cette technique ne présente aucun danger connu pour la santé des sujets. Historique Charles Roy et Charles Sherrington furent les premiers à faire le lien entre l'activité cérébrale et le flux sanguin, à l'université de Cambridge. Principe vignette|gauche|IRMf de la tête d'un

Source officielle

https://fr.wikipedia.org/wiki/Imagerie_par_r%C3%A9sonance_magn%C3%A9tique_fonctionnelle

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Over the last decade, technological advances in the field of functional magnetic resonance imaging (fMRI) have made it possible to obtain localized measures of brain activity in real-time. This allows for applications such as online quality control of the acquisition, intra-operative fMRI, brain-computer-interfaces, and neurofeedback (NFB). Real-time fMRI (rt-fMRI) NFB studies have shown that a variety of different regions of interest (ROI) can be regulated in healthy and clinical populations, and by this, set the ground to become a potential non-invasive modulation. Moreover, other advances in the field of fMRI data analysis include functional connectivity, aiming to investigate interactions between distant brain regions. These studies have the potential to inform recent interest in the human brain âconnectome.â Our work combines these two advances in the field of fMRI, and so we investigate the impact rt-fMRI NFB has on functional network organization, with the perspective of offering improved and more advanced neurofeedback. In our work, we focus on rt-fMRI NFB based on the auditory region as a single ROI, conducted with auditory stimuli on healthy subjects. In a series of papers, first, we report that subjects can downregulate activity of their right auditory cortex and that activity of the default mode network recovers via unique time courses in at least four of its components. Second, in the context of self-regulation, we utilized data-driven independent component analysis to reveal the auditory cortex as the main hub of functional connectivity changes, with changes also occurring in the brainstem, auditory pathway, and higher order areas involved in vision, attention, and working memory. Third, we utilized multivariate analyses and cross-validation to reveal 16 brain regions associated with self-regulation training. Subjects showed one of two distinct patterns of co-activation, suggesting that differences in connectivity may be related to differences in learning strategies. Finally, a meta-analysis based on several rt-fMRI NFB publications, had shown a large regulation network, including the anterior cingulate cortex, anterior insula, and the basal ganglia. This network could be involved in the underlying mechanism of self-regulation, and could improve future design of connectivity based rt-fMRI feedback. Our studies extend initial proof-of-concept studies indicating that subjects can self-regulate their own auditory cortex and go on to show that the impact of a single ROI regulation induces global network effects. In sum, we provide a comprehensive view of functional connectivity changes that occur throughout the brain with neurofeedback-based fMRI training. Those studies have the potential to advance the development of network-based rt-fMRI NFB for tinnitus clinical population, and also for other diseases that have network characteristics.

EPFL2017

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Major theories on the neural basis of schizophrenic core symptoms highlight aberrant salience network activity (insula and anterior cingulate cortex), prefrontal hypoactivation, sensory processing deficits as well as an impaired connectivity between temporal and prefrontal cortices. The mismatch negativity is a potential biomarker of schizophrenia and its reduction might be a consequence of each of these mechanisms. In contrast to the previous electroencephalographic studies, functional magnetic resonance imaging may disentangle the involved brain networks at high spatial resolution and determine contributions from localized brain responses and functional connectivity to the schizophrenic impairments. Twenty-four patients and 24 matched control subjects underwent functional magnetic resonance imaging during an optimized auditory mismatch task. Haemodynamic responses and functional connectivity were compared between groups. These data sets further entered a diagnostic classification analysis to assess impairments on the individual patient level. In the control group, mismatch responses were detected in the auditory cortex, prefrontal cortex and the salience network (insula and anterior cingulate cortex). Furthermore, mismatch processing was associated with a deactivation of the visual system and the dorsal attention network indicating a shift of resources from the visual to the auditory domain. The patients exhibited reduced activation in all of the respective systems (right auditory cortex, prefrontal cortex, and the salience network) as well as reduced deactivation of the visual system and the dorsal attention network. Group differences were most prominent in the anterior cingulate cortex and adjacent prefrontal areas. The latter regions also exhibited a reduced functional connectivity with the auditory cortex in the patients. In the classification analysis, haemodynamic responses yielded a maximal accuracy of 83% based on four features; functional connectivity data performed similarly or worse for up to about 10 features. However, connectivity data yielded a better performance when including more than 10 features yielding up to 90% accuracy. Among others, the most discriminating features represented functional connections between the auditory cortex and the anterior cingulate cortex as well as adjacent prefrontal areas. Auditory mismatch impairments incorporate major neural dysfunctions in schizophrenia. Our data suggest synergistic effects of sensory processing deficits, aberrant salience attribution, prefrontal hypoactivation as well as a disrupted connectivity between temporal and prefrontal cortices. These deficits are associated with subsequent disturbances in modality-specific resource allocation. Capturing different schizophrenic core dysfunctions, functional magnetic resonance imaging during this optimized mismatch paradigm reveals processing impairments on the individual patient level, rendering it a potential biomarker of schizophrenia.

Oxford University Press2015

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Auditory verbal hallucinations (AVHs) are a hallmark of schizophrenia and can significantly impair patients' emotional, social, and occupational functioning. Despite progress in psychopharmacology, over 25% of schizophrenia patients suffer from treatment-resistant hallucinations. In the search for alternative treatment methods, neurofeedback (NF) emerges as a promising therapy tool. NF based on real-time functional magnetic resonance imaging (rt-fMRI) allows voluntarily change of the activity in a selected brain region - even in patients with schizophrenia. This study explored effects of NF on ongoing AVHs. The selected participants were trained in the self-regulation of activity in the anterior cingulate cortex (ACC), a key monitoring region involved in generation and intensity modulation of AVHs. Using rt-fMRI, three right-handed patients, suffering from schizophrenia and ongoing, treatment-resistant AVHs, learned control over ACC activity on three separate days. The effect of NF training on hallucinations' severity was assessed with the Auditory Vocal Hallucination Rating Scale (AVHRS) and on the affective state - with the Positive and Negative Affect Schedule (PANAS). All patients yielded significant upregulation of the ACC and reported subjective improvement in some aspects of AVHs (AVHRS) such as disturbance and suffering from the voices. In general, mood (PANAS) improved during NF training, though two patients reported worse mood after NF on the third day. ACC and reward system activity during NF learning and specific effects on mood and symptoms varied across the participants. None of them profited from the last training set in the prolonged three-session training. Moreover, individual differences emerged in brain networks activated with NF and in symptom changes, which were related to the patients' symptomatology and disease history. NF based on rt-fMRI seems a promising tool in therapy of AVHs. The patients, who suffered from continuous hallucinations for years, experienced symptom changes that may be attributed to the NF training. In order to assess the effectiveness of NF as a therapeutic method, this effect has to be studied systematically in larger groups; further, long-term effects need to be assessed. Particularly in schizophrenia, future NF studies should take into account the individual differences in reward processing, fatigue, and motivation to develop individualized training protocols.

Frontiers Media Sa2016

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Oxford University Press2015

EPFL2017

Frontiers Media Sa2016