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Peter Stiers

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9 papers

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YNICL Journal 2026 Journal Article

Depression vulnerability involves brain activity and connectivity changes consistent with cholinergic deviancy

Peter Stiers
Zoe Samara
Kyran J.R. Kuijpers
Elisabeth A.T. Evers
Johannes G. Ramaekers

Behavioral and imaging studies suggests that emotional biases in the perception of faces associated with major depression disorder (MD) may be embedded within a broader sensory processing deficit. Increased cortical acetylcholine in MD suggest that this deficit may be related to abnormal attention modulation of sensory areas. It is not clear, however, whether these problems are a manifestation of the disease or whether they precede symptom onset. To investigate this, we applied functional magnetic resonance imaging (fMRI) to look for brain activity changes that participants with a family risk of MD (N = 30) shared with participant with MD (N = 28), compared to matched controls (N = 28). Participants were scanned while performing gender categorization of sad, happy, and neutral face pictures, as well as during a state of rest. Task-related activity changes, shared by participants at risk of and suffering from MD, were mostly seen in the posterior brain: increased activity in dorsal attention and visual association cortex, and decreased in lower visual areas. The changes did not differ between neutral faces and faces expressing an emotion. The at risk and MD participants additionally showed increased functional connectivity between the dorsal attention clusters and the lingual gyrus, and decreased connectivity with the lateral occipital complex (LOC). Lastly, they also had in common increased functional connectivity of magnocellular basal forebrain seeds with LOC and visual association cortex. These changes are consistent with an acetylcholine-mediated change in attention-guided sensory processing of all environmental events, which is discernable even before the first MD episode.

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YNIMG Journal 2016 Journal Article

Reverse inference of memory retrieval processes underlying metacognitive monitoring of learning using multivariate pattern analysis

Peter Stiers
Luciana Falbo
Alexandros Goulas
Tamara van Gog
Anique de Bruin

Monitoring of learning is only accurate at some time after learning. It is thought that immediate monitoring is based on working memory, whereas later monitoring requires re-activation of stored items, yielding accurate judgements. Such interpretations are difficult to test because they require reverse inference, which presupposes specificity of brain activity for the hidden cognitive processes. We investigated whether multivariate pattern classification can provide this specificity. We used a word recall task to create single trial examples of immediate and long term retrieval and trained a learning algorithm to discriminate them. Next, participants performed a similar task involving monitoring instead of recall. The recall-trained classifier recognized the retrieval patterns underlying immediate and long term monitoring and classified delayed monitoring examples as long-term retrieval. This result demonstrates the feasibility of decoding cognitive processes, instead of their content.

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YNIMG Journal 2012 Journal Article

Maturation of task-induced brain activation and long range functional connectivity in adolescence revealed by multivariate pattern classification

Esther H.H. Keulers
Alexandros Goulas
Jelle Jolles
Peter Stiers

The present study uses multivariate pattern classification analysis to examine maturation in task-induced brain activation and in functional connectivity during adolescence. The multivariate approach allowed accurate discrimination of adolescent boys of respectively 13, 17 and 21years old based on brain activation during a gonogo task, whereas the univariate statistical analyses showed no or only very few, small age-related clusters. Developmental differences in task activation were spatially distributed throughout the brain, indicating differences in the responsiveness of a wide range of task-related and default mode regions. Moreover, these distributed age-distinctive patterns generalized from a simple gonogo task to a cognitively and motivationally very different gambling task, and vice versa. This suggests that functional brain maturation in adolescence is driven by common processes across cognitive tasks as opposed to task-specific processes. Although we confirmed previous reports of age-related differences in functional connectivity, particularly for long range connections (>60mm), these differences were not specific to brain regions that showed maturation of task-induced responsiveness. Together with the task-independency of brain activation maturation, this result suggests that brain connectivity changes in the course of adolescence affect brain functionality at a basic level. This basic change is manifest in a range of tasks, from the simplest gonogo task to a complex gambling task.

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YNIMG Journal 2012 Journal Article

The “why” and “how” of JointICA: Results from a visual detection task

Bogdan Mijović
Katrien Vanderperren
Nikolay Novitskiy
Bart Vanrumste
Peter Stiers
Bea Van den Bergh
Lieven Lagae
Stefan Sunaert

Since several years, neuroscience research started to focus on multimodal approaches. One such multimodal approach is the combination of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). However, no standard integration procedure has been established so far. One promising data-driven approach consists of a joint decomposition of event-related potentials (ERPs) and fMRI maps derived from the response to a particular stimulus. Such an algorithm (joint independent component analysis or JointICA) has recently been proposed by Calhoun et al. (2006). This method provides sources with both a fine spatial and temporal resolution, and has shown to provide meaningful results. However, the algorithm's performance has not been fully characterized yet, and no procedure has been proposed to assess the quality of the decomposition. In this paper, we therefore try to answer why and how JointICA works. We show the performance of the algorithm on data obtained in a visual detection task, and compare the performance for EEG recorded simultaneously with fMRI data and for EEG recorded in a separate session (outside the scanner room). We perform several analyses in order to set the necessary conditions that lead to a sound decomposition, and to give additional insights for exploration in future studies. In that respect, we show how the algorithm behaves when different EEG electrodes are used and we test the robustness with respect to the number of subjects in the study. The performance of the algorithm in all the experiments is validated based on results from previous studies.

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YNIMG Journal 2011 Journal Article

Developmental changes between ages 13 and 21 years in the extent and magnitude of the BOLD response during decision making

Esther H.H. Keulers
Peter Stiers
Jelle Jolles

Developmental neuroimaging results have suggested a progression in focalization in functional activations from childhood to adulthood. The mechanisms underlying this process are thought to be an age-related decrease in activation extent as well as an increased magnitude in task-related areas. The present study aimed to evaluate these notions while controlling for confounders that may bias towards focalization. We used adolescent subjects in small age ranges. In addition, head motion corrections were incorporated in statistical analyses and regions of interest were identified for each participant separately to overcome inter-individual variability in anatomy and functional organization. Activation patterns of 13-, 17- and 21-year-old males were compared during the decision phase of a challenging and complex gambling paradigm. The BOLD amplitude enhanced with increasing age, modulated by task conditions. First, response amplitude during difficult, endogenous relative to exogenous decisions increased with age. This decision difficulty effect was most pronounced in 21-year-olds, both in areas associated with task execution and default mode areas. Second, deciding to pass as opposed to gamble exerted more effort in inferior frontal and parietal areas only by 13- and 17-year-olds. There was neither an age-related decrease in activation extent, nor any qualitative shifts in activated areas as suggested by the focalization hypothesis. These results suggest that although different age groups throughout adolescence engage similar brain areas during decision making, the response magnitude in these areas increases with age particularly during difficult task conditions, providing that confounding factors are controlled.

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YNIMG Journal 2010 Journal Article

Distributed task coding throughout the multiple demand network of the human frontal–insular cortex

Peter Stiers
Maarten Mennes
Stefan Sunaert

The large variety of tasks that humans can perform is governed by a small number of key frontal–insular regions that are commonly active during task performance. Little is known about how this network distinguishes different tasks. We report on fMRI data in twelve participants while they performed four cognitive tasks. Of 20 commonly active frontal–insular regions in each hemisphere, five showed a BOLD response increase with increased task demands, regardless of the task. Although active in all tasks, each task invoked a unique response pattern across the voxels in each area that proved reliable in split-half multi-voxel correlation analysis. Consequently, voxels differed in their preference for one or more of the tasks. Voxel-based functional connectivity analyses revealed that same preference voxels distributed across all areas of the network constituted functional sub-networks that characterized the task being executed.

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YNIMG Journal 2010 Journal Article

Removal of BCG artifacts from EEG recordings inside the MR scanner: A comparison of methodological and validation-related aspects

Katrien Vanderperren
Maarten De Vos
Jennifer R. Ramautar
Nikolay Novitskiy
Maarten Mennes
Sara Assecondi
Bart Vanrumste
Peter Stiers

Multimodal approaches are of growing interest in the study of neural processes. To this end much attention has been paid to the integration of electroencephalographic (EEG) and functional magnetic resonance imaging (fMRI) data because of their complementary properties. However, the simultaneous acquisition of both types of data causes serious artifacts in the EEG, with amplitudes that may be much larger than those of EEG signals themselves. The most challenging of these artifacts is the ballistocardiogram (BCG) artifact, caused by pulse-related electrode movements inside the magnetic field. Despite numerous efforts to find a suitable approach to remove this artifact, still a considerable discrepancy exists between current EEG-fMRI studies. This paper attempts to clarify several methodological issues regarding the different approaches with an extensive validation based on event-related potentials (ERPs). More specifically, Optimal Basis Set (OBS) and Independent Component Analysis (ICA) based methods were investigated. Their validation was not only performed with measures known from previous studies on the average ERPs, but most attention was focused on task-related measures, including their use on trial-to-trial information. These more detailed validation criteria enabled us to find a clearer distinction between the most widely used cleaning methods. Both OBS and ICA proved to be able to yield equally good results. However, ICA methods needed more parameter tuning, thereby making OBS more robust and easy to use. Moreover, applying OBS prior to ICA can optimize the data quality even more, but caution is recommended since the effect of the additional ICA step may be strongly subject-dependent.

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YNIMG Journal 2007 Journal Article

Linear normalization of MR brain images in pediatric patients with periventricular leukomalacia

Bart Machilsen
Emiliano d'Agostino
Frederik Maes
Dirk Vandermeulen
Horst K. Hahn
Lieven Lagae
Peter Stiers

The feasibility of linear normalization of child brain images with structural abnormalities due to periventricular leukomalacia (PVL) was assessed in terms of success rate and accuracy of the normalization algorithm. Ten T1-weighted brain images from healthy adult subject and 51 from children (4–11 years of age) were linearly transformed to achieve spatial registration with the standard MNI brain template. Twelve of the child brain images were radiologically normal, 22 showed PVL and 17 showed PVL with additional enlargement of the lateral ventricles. The effects of simple modifications to the normalization process were evaluated: changing the initial orientation and zoom parameters, masking non-brain areas, smoothing the images and using a pediatric template instead of the MNI template. Normalization failure was reduced by changing the initial zoom parameters and by removing background noise. The overall performance of the normalization algorithm was only improved when background noise was removed from the images. The results show that linear normalization of PVL affected brain images is feasible.

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YNIMG Journal 2006 Journal Article

Mapping multiple visual areas in the human brain with a short fMRI sequence

Peter Stiers
Ronald Peeters
Lieven Lagae
Paul Van Hecke
Stefan Sunaert

It is a fundamental insight of neuroscience that the cerebral cortex is divided into spatially separated and functionally distinct areas. In this study, we tried to map a large number of visual areas in individual subjects passively viewing a simple stimulus sequence during functional magnetic resonance imaging (fMRI) at 1. 5 T. The blocked stimulus sequence contrasted static object photographs with video takes of movement through natural indoor and outdoor scenes, alternated with a control fixation task. Two runs of the 5-min sequence sufficed to invoke 29 distinguishable activations, 16 (13 bilateral) of which were observed in all 10 participants. At the ventral side, object responsive activations were organized along the lateral occipital–temporal surface and near the collateral and occipital–temporal sulci. The latter activations, corresponding to the lateral occipital complex, showed a different activation profile from those near the collateral sulcus, most likely corresponding to the color constancy areas V4/V8–V4α. A potentially new fusiform object area was seen in 6 subjects, even more anterior than the parahippocampal place area. At the dorsal side, consistent activations were mainly related to motion stimuli and included the well-known areas V3a, VIPS, POIPS, hV5+, STS and the cingulate sulcus. There was consistent activation in the parietal–occipital sulcus, containing the areas V6a and V6. In addition, all subjects showed activation in the superior–anterior precuneus. Thus, the short stimulus sequence robustly invoked multiple visual areas and can be used to map the organization of the visual system in normal and brain-damaged individuals.

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