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Mohamed Ali Bahri

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7 papers

1 author row

YNIMG Journal 2020 Journal Article

Age-related differences in the neural correlates of vivid remembering

Adrien Folville
Mohamed Ali Bahri
Emma Delhaye
Eric Salmon
Arnaud D’Argembeau
Christine Bastin

When recollecting events, older adults typically report similar memory vividness levels as young adults, while they actually retrieve fewer episodic details. This suggests that young and older adults use episodic details differently to calibrate their vividness judgements. Capitalizing on the idea that remembering reactivates brain regions that initially processed details at encoding, the current fMRI study sought to examine these age-related changes in the basis of vivid recollection. At encoding, young and older adults saw pictures associated with labels and these labels were then used as retrieval cues for recalling the associated pictures and making memory vividness judgments. Results showed that highly vivid memories were associated with greater activity in the precuneus in young than older adults. Furthermore, the direct comparison between encoding and retrieval patterns of activity using Representational Similarity Analyses revealed stronger item-specific reactivation in the posterior cingulate/retrosplenial cortex in young than older adults. Taken together, these results provide new evidence that aging is associated with reduced reinstatement of activity in brain regions that processed the encoding of complex stimuli, but older individuals judge these impoverished memory representations as subjectively vivid.

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YNICL Journal 2019 Journal Article

Alzheimer's disease patients activate attention networks in a short-term memory task

Sophie Kurth
Mohamed Ali Bahri
Fabienne Collette
Christophe Phillips
Steve Majerus
Christine Bastin
Eric Salmon

Network functioning during cognitive tasks is of major interest in Alzheimer's disease (AD). Cognitive functioning in AD includes variable performance in short-term memory (STM). In most studies, the verbal STM functioning in AD patients has been interpreted within the phonological loop subsystem of Baddeley's working memory model. An alternative account considers that domain-general attentional processes explain the involvement of frontoparietal networks in verbal STM beside the functioning of modality-specific subsystems. In this study, we assessed the functional integrity of the dorsal attention network (involved in task-related attention) and the ventral attention network (involved in stimulus-driven attention) by varying attentional control demands in a STM task. Thirty-five AD patients and twenty controls in the seventies performed an fMRI STM task. Variation in load (five versus two items) allowed the dorsal (DAN) and ventral attention networks (VAN) to be studied. ANOVA revealed that performance decreased with increased load in both groups. AD patients performed slightly worse than controls, but accuracy remained above 70% in all patients. Statistical analysis of fMRI brain images revealed DAN activation for high load in both groups. There was no between-group difference or common activation for low compared to high load conditions. Psychophysiological interaction showed a negative relationship between the DAN and the VAN for high versus low load conditions in patients. In conclusion, the DAN remained activated and connected to the VAN in mild AD patients who succeeded in performing an fMRI verbal STM task. DAN was necessary for the task, but not sufficient to reach normal performance. Slightly lower performance in early AD patients compared to controls might be related to maintained bottom-up attention to distractors, to decrease in executive functions, to impaired phonological processing or to reduced capacity in serial order processing.

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YNICL Journal 2017 Journal Article

Altered functional brain connectivity in patients with visually induced dizziness

Angelique Van Ombergen
Lizette Heine
Steven Jillings
R. Edward Roberts
Ben Jeurissen
Vincent Van Rompaey
Viviana Mucci
Stefanie Vanhecke

BACKGROUND: Vestibular patients occasionally report aggravation or triggering of their symptoms by visual stimuli, which is called visually induced dizziness (VID). These patients therefore experience dizziness, discomfort, disorientation and postural unsteadiness. The underlying pathophysiology of VID is still poorly understood. OBJECTIVE: The aim of the current explorative study was to gain a first insight in the underlying neural aspects of VID. METHODS: We included 10 VID patients and 10 healthy matched controls, all of which underwent a resting state fMRI scan session. Changes in functional connectivity were explored by means of the intrinsic connectivity contrast (ICC). Seed-based analysis was subsequently performed in visual and vestibular seeds. RESULTS: We found a decreased functional connectivity in the right central operculum (superior temporal gyrus), as well as increased functional connectivity in the occipital pole in VID patients as compared to controls in a hypothesis-free analysis. A weaker functional connectivity between the thalamus and most of the right putamen was measured in VID patients in comparison to controls in a seed-based analysis. Furthermore, also by means of a seed-based analysis, a decreased functional connectivity between the visual associative area and the left parahippocampal gyrus was found in VID patients. Additionally, we found increased functional connectivity between thalamus and occipital and cerebellar areas in the VID patients, as well as between the associative visual cortex and both middle frontal gyrus and precuneus. CONCLUSIONS: We found alterations in the visual and vestibular cortical network in VID patients that could underlie the typical VID symptoms such as a worsening of their vestibular symptoms when being exposed to challenging visual stimuli. These preliminary findings provide the first insights into the underlying functional brain connectivity in VID patients. Future studies should extend these findings by employing larger sample sizes, by investigating specific task-based paradigms in these patients and by exploring the implications for treatment.

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YNIMG Journal 2016 Journal Article

Neural correlates of event clusters in past and future thoughts: How the brain integrates specific episodes with autobiographical knowledge

Julie Demblon
Mohamed Ali Bahri
Arnaud D'Argembeau

When remembering the past or envisioning the future, events often come to mind in organized sequences or stories rather than in isolation from one another. The aim of the present fMRI study was to investigate the neural correlates of such event clusters. Participants were asked to consider pairs of specific past or future events: in one condition, the two events were part of the same event cluster (i. e. , they were thematically and/or causally related to each other), whereas in another condition the two events only shared a surface feature (i. e. , their location); a third condition was also included, in which the two events were unrelated to each other. The results showed that the processing of past and future events that were part of a same cluster was associated with higher activation in the medial prefrontal cortex (PFC), rostrolateral PFC, and left lateral temporal and parietal regions, compared to the two other conditions. Furthermore, functional connectivity analyses revealed an increased coupling between these cortical regions. These findings suggest that largely similar processes are involved in organizing events in clusters for the past and the future. The medial and rostrolateral PFC might play a pivotal role in mediating the integration of specific events with conceptual autobiographical knowledge ‘stored’ in more posterior regions. Through this integrative process, this set of brain regions might contribute to the attribution of an overarching meaning to representations of specific past and future events, by contextualizing them with respect to personal goals and general knowledge about one's life story.

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YNIMG Journal 2013 Journal Article

Metabolic and structural connectivity within the default mode network relates to working memory performance in young healthy adults

Igor Yakushev
Gael Chételat
Florian U. Fischer
Brigitte Landeau
Christine Bastin
Armin Scheurich
Audrey Perrotin
Mohamed Ali Bahri

Studies of functional connectivity suggest that the default mode network (DMN) might be relevant for cognitive functions. Here, we examined metabolic and structural connectivity between major DMN nodes, the posterior cingulate (PCC) and medial prefrontal cortex (MPFC), in relation to normal working memory (WM). DMN was captured using independent component analysis of [18F]fluorodeoxyglucose positron emission tomography (FDG-PET) data from 35 young healthy adults (27. 1±5. 1years). Metabolic connectivity, a correlation between FDG uptake in PCC and MPFC, was examined in groups of subjects with (relative to median) low (n=18) and high (n=17) performance on digit span backward test as an index of verbal WM. In addition, fiber tractography based on PCC and MPFC nodes as way points was performed in a subset of subjects. FDG uptake in the DMN nodes did not differ between high and low performers. However, significantly (p=0. 01) lower metabolic connectivity was found in the group of low performers. Furthermore, as compared to high performers, low performers showed lower density of the left superior cingulate bundle. Verbal WM performance is related to metabolic and structural connectivity within the DMN in young healthy adults. Metabolic connectivity as quantified with FDG-PET might be a sensitive marker of the normal variability in some cognitive functions.

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YNIMG Journal 2013 Journal Article

Relationships between brain metabolism decrease in normal aging and changes in structural and functional connectivity

Gaël Chételat
Brigitte Landeau
Eric Salmon
Igor Yakushev
Mohamed Ali Bahri
Florence Mézenge
Audrey Perrotin
Christine Bastin

Normal aging is characterized by brain glucose metabolism decline predominantly in the prefrontal cortex. The goal of the present study was to assess whether this change was associated with age-related alteration of white matter (WM) structural integrity and/or functional connectivity. FDG-PET data from 40 young and 57 elderly healthy participants from two research centers (n=49/48 in Center 1/2) were analyzed. WM volume from T1-weighted MRI (Center 1), fractional anisotropy from diffusion-tensor imaging (Center 2), and resting-state fMRI data (Center 1) were also obtained. Group comparisons were performed within each imaging modality. Then, positive correlations were assessed, within the elderly, between metabolism in the most affected region and the other neuroimaging modalities. Metabolism decline in the elderly predominated in the left inferior frontal junction (LIFJ). LIFJ hypometabolism was significantly associated with macrostructural and microstructural WM disturbances in long association fronto-temporo-occipital fibers, while no relationship was found with functional connectivity. The findings offer new perspectives to understand normal aging processes and open avenues for future studies to explore causality between age-related metabolism and connectivity changes.

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YNIMG Journal 2012 Journal Article

Cognitive reserve impacts on inter-individual variability in resting-state cerebral metabolism in normal aging

Christine Bastin
Igor Yakushev
Mohamed Ali Bahri
Andreas Fellgiebel
Francis Eustache
Brigitte Landeau
Armin Scheurich
Dorothée Feyers

There is a great deal of heterogeneity in the impact of aging on cognition and cerebral functioning. One potential factor contributing to individual differences among the elderly is the cognitive reserve, which designates the partial protection from the deleterious effects of aging that lifetime experience provides. Neuroimaging studies examining task-related activation in elderly people suggested that cognitive reserve takes the form of more efficient use of brain networks and/or greater ability to recruit alternative networks to compensate for age-related cerebral changes. In this exploratory multi-center study, we examined the relationships between cognitive reserve, as measured by education and verbal intelligence, and cerebral metabolism at rest (FDG-PET) in a sample of 74 healthy older participants. Higher degree of education and verbal intelligence was associated with less metabolic activity in the right posterior temporoparietal cortex and the left anterior intraparietal sulcus. Functional connectivity analyses of resting-state fMRI images in a subset of 41 participants indicated that these regions belong to the default mode network and the dorsal attention network respectively. Lower metabolism in the temporoparietal cortex was also associated with better memory abilities. The findings provide evidence for an inverse relationship between cognitive reserve and resting-state activity in key regions of two functional networks respectively involved in internal mentation and goal-directed attention.

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