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Christoph Michel

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7 papers
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7

YNICL Journal 2018 Journal Article

Automated diagnosis of temporal lobe epilepsy in the absence of interictal spikes

  • Thibault Verhoeven
  • Ana Coito
  • Gijs Plomp
  • Aljoscha Thomschewski
  • Francesca Pittau
  • Eugen Trinka
  • Roland Wiest
  • Karl Schaller

Objective: To diagnose and lateralise temporal lobe epilepsy (TLE) by building a classification system that uses directed functional connectivity patterns estimated during EEG periods without visible pathological activity. Methods: Resting-state high-density EEG recording data from 20 left TLE patients, 20 right TLE patients and 35 healthy controls was used. Epochs without interictal spikes were selected. The cortical source activity was obtained for 82 regions of interest and whole-brain directed functional connectivity was estimated in the theta, alpha and beta frequency bands. These connectivity values were then used to build a classification system based on two two-class Random Forests classifiers: TLE vs healthy controls and left vs right TLE. Feature selection and classifier training were done in a leave-one-out procedure to compute the mean classification accuracy. Results: The diagnosis and lateralization classifiers achieved a high accuracy (90.7% and 90.0% respectively), sensitivity (95.0% and 90.0% respectively) and specificity (85.7% and 90.0% respectively). The most important features for diagnosis were the outflows from left and right medial temporal lobe, and for lateralization the right anterior cingulate cortex. The interaction between features was important to achieve correct classification. Significance: This is the first study to automatically diagnose and lateralise TLE based on EEG. The high accuracy achieved demonstrates the potential of directed functional connectivity estimated from EEG periods without visible pathological activity for helping in the diagnosis and lateralization of TLE.

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YNIMG Journal 2014 Journal Article

EEG source imaging of brain states using spatiotemporal regression

  • Anna Custo
  • Serge Vulliemoz
  • Frederic Grouiller
  • Dimitri Van De Ville
  • Christoph Michel

Relating measures of electroencephalography (EEG) back to the underlying sources is a long-standing inverse problem. Here we propose a new method to estimate the EEG sources of identified electrophysiological states that represent spontaneous activity, or are evoked by a stimulus, or caused by disease or disorder. Our method has the unique advantage of seamlessly integrating a statistical significance of the source estimate while efficiently eliminating artifacts (e. g. , due to eye blinks, eye movements, bad electrodes). After determining the electrophysiological states in terms of stable topographies using established methods (e. g. : ICA, PCA, k-means, epoch average), we propose to estimate these states' time courses through spatial regression of a General Linear Model (GLM). These time courses are then used to find EEG sources that have a similar time-course (using temporal regression of a second GLM). We validate our method using both simulated and experimental data. Simulated data allows us to assess the difference between source maps obtained by the proposed method and those obtained by applying conventional source imaging of the state topographies. Moreover, we use data from 7 epileptic patients (9 distinct epileptic foci localized by intracranial EEG) and 2 healthy subjects performing an eyes-open/eyes-closed task to elicit activity in the alpha frequency range. Our results indicate that the proposed EEG source imaging method accurately localizes the sources for each of the electrical brain states. Furthermore, our method is particularly suited for estimating the sources of EEG resting states or otherwise weak spontaneous activity states, a problem not adequately solved before.

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YNIMG Journal 2006 Journal Article

The fusiform face area is tuned for curvilinear patterns with more high-contrasted elements in the upper part

  • Roberto Caldara
  • Mohamed L. Seghier
  • Bruno Rossion
  • Francois Lazeyras
  • Christoph Michel
  • Claude-Alain Hauert

The ability to identify conspecifics from the face is of primary interest for human social behavior. Newborns' visual preference for schematic face-like stimuli has been recently related to a sensitivity for visual patterns with a greater number of elements in the upper compared to the lower part. At the adult level, neuroimaging studies have identified a network of cortical areas devoted to the detection and identification of faces. However, whether and how low-level structural properties of face stimuli contribute to the preferential response to faces in these areas remain to be clarified. Using functional magnetic resonance imaging (fMRI), here we investigated whether the adults' face-sensitive cortical areas show a preference for top-heavy patterns, similarly to newborns' preference. Twelve participants were presented with head-shaped and square patterns with either more elements in the upper or the lower vertical part. In the right fusiform gyrus (‘fusiform face area’, FFA), an area showing a preference for faces over other visual object categories, there was a larger activation for curvilinear patterns with more high-contrast elements in the upper part, even though these patterns were not perceived as face stimuli. These findings provide direct evidence that the FFA is tuned for geometrical properties fitting best with the structure of faces, a computational mechanism that might drive the automatic detection of faces in the visual world.

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YNIMG Journal 2005 Journal Article

Hemispheric specialization of human inferior temporal cortex during coarse-to-fine and fine-to-coarse analysis of natural visual scenes

  • Carole Peyrin
  • Sophie Schwartz
  • Mohamed Seghier
  • Christoph Michel
  • Theodor Landis
  • Patrik Vuilleumier

Recent models of visual recognition have suggested that perceptual analysis may start with a parallel extraction of different spatial frequencies (SF), using a preferential coarse-to-fine (low-to-high SF) sequence of processing. A rapid extraction of low spatial frequency (LSF) information may thus provide an initial and crude parsing of the visual scene, subsequently refined by slow but more detailed high spatial frequency (HSF) information. However, the sequence of SF analysis could be flexible, a high-to-low (HtL) being sometimes preferred to a low-to-high (LtH) SF sequence depending on task demands. Furthermore, it has also been suggested that the right vs. left hemisphere might be differentially specialized in LSF vs. HSF analysis, respectively. By manipulating the temporal succession of LSF and HSF stimuli, the present fMRI study investigated whether such hemispheric specialization may underlie the flexible use of different time-course in SF analysis. Participants performed a matching task between two successive images of natural scenes (LSF or HSF) that were displayed either in an LtH (LSF scene presented first and HSF scene second) or in a reverse HtL sequence. A direct inter-hemispheric comparison of the neural responses evoked by each SF sequence revealed greater activations within the right occipito-temporal cortex for the LtH sequence and within the left occipito-temporal cortex for the HtL sequence. These fMRI results suggest that the hemisphere preferentially engaged during the sequential processing of different SF might be determined by the initial SF-band appearing in this sequence, and that both a coarse-to-fine and fine-to-coarse analysis might independently take place in the two hemispheres.

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YNIMG Journal 2005 Journal Article

Two electrophysiological stages of spatial orienting towards fearful faces: early temporo-parietal activation preceding gain control in extrastriate visual cortex

  • Gilles Pourtois
  • Gregor Thut
  • Rolando Grave de Peralta
  • Christoph Michel
  • Patrik Vuilleumier

Visuo-spatial attention tends to be prioritized towards emotionally negative stimuli such as fearful faces, as opposed to neutral or positive stimuli. Using a covert orienting task, we previously showed that a lateral occipital P1 component, with extrastriate neural sources, was selectively enhanced to lateralized visual targets replacing a fearful face (fear-valid trial) than the same targets replacing a neutral face (fear-invalid trial), providing evidence for exogenous spatial orienting of attention towards threat cues. Here, we describe a new analysis of these data, using topographic evoked potentials mapping methods combined with a distributed source localization technique. We show that an early field topography (40–80 ms post-target onset) with a centro-parietal negativity and a left posterior parietal source distinguished fear-valid from fear-invalid trials, whereas a distinct activity with anterior cingulate sources was selectively evoked during fear-invalid trials. At the same latency, or later, no difference in field topography was found for valid compared to invalid trials with happy faces. The early parietal map preceded a modulation in amplitude of the field strength (∼130ms), corresponding to the enhanced lateral occipital P1 during valid trials in the fear condition. Furthermore, this early topography at 40–80 ms was positively correlated with the subsequent amplitude modulation of P1 at 130–160 ms in the fear condition, suggesting a possible functional coupling between these two successive events. These data have important implications for models of spatial attention and interactions with emotion. They suggest two successive stages of neural activity during exogenous orienting of attention towards visual targets following fearful faces, including an early posterior parietal negativity, followed by gain control mechanisms enhancing visual responses in extrastriate occipital cortex.

Details DOI
v2026.09.13