Biomedical subjects

J R Foucher

Publications and source records attributed to J R Foucher.

5 recordsLinked to original sources

PubMed2006

Optimisation of a post-processing method to remove the pulse artifact from EEG data recorded during fMRI: an application to P300 recordings during e-fMRI.

In functional cerebral studies, it has been established that co-registered electroencephalography (EEG) measurements and functional magnetic resonance imaging (fMRI) were complementary. However, EEG data recorded inside an MRI scanner are heavily distorted, mainly by the most prominent artifact, the cardiac pulse artifact (PA). We describe an original algorithm which yields a high-quality PA filter and demonstrates how this tool can be used to improve the quality of P300 ERP measurements during event-related fMRI (e-fMRI) experiments. EEG data were acquired in interleaved mode during e-fMRI while six healthy volunteers performed a visual odd-ball task, involving Distractors, Target and Novel stimuli, to elicit P300 components. The PA was corrected with the original algorithm. The temporal variations in the PA were evidenced using a principal component analysis (PCA), on each EEG channel. The procedure yielded several PA templates, which were regressed from the EEG data. The PA removal procedure was optimised, and then implemented to improve the measured P300 components. Regressing the most adequate PA template resulted in a high-quality reduction in spectral power at frequencies associated with the cardiac PA. More reliable P300 component measurements were obtained, evidencing higher amplitudes for Novels (9.76-11.20 microV) than for to Targets (6.3-9.09 microV) in centro-parietal and prefrontal areas. The improvement of the processing of EEG data acquired simultaneously with fMRI data provides a new tool and casts perspectives to study the functional organisation of the brain.

Adult↗

PubMed2005

Functional integration in schizophrenia: too little or too much? Preliminary results on fMRI data.

The disconnectivity hypothesis proposes that schizophrenia results from poor or miswired anatomical connections. Theoretically, its functional counterpart should be disintegration. Integration is thought to allow segregated neurons to interact as a coherent whole, referred to as the "core", while the non-interacting part of the brain is referred to as the "rest". In this study, it is suggested that schizophrenia is the result of rest noise interfering with core activity. Two possible causes are assessed: (i) defective core integration, making the core more vulnerable to noise from the rest, or (ii) the rest being too highly integrated, meaning that it can interfere with the core. These hypotheses were tested using fMRI data acquired from 13 stabilized medicated schizophrenic subjects compared to 11 matched controls. Subjects were required to perform a series of lexical decision and retrieval tasks in separate sessions. The brain was divided into 90 components. Integration was defined as the amount of information shared between the components of a sub-system. An iterative aggregation procedure made it possible to identify a core on the basis of the functional clustering index, which assesses the integration of the core relative to its integration with the rest. Correlation of component-pairs within the core was also compared between the two groups. This procedure was repeated for each subject and for each task. Cores did not differ between the two groups, either in terms of integration or in terms of functional clustering index. However, the core was still highly integrated with the rest and the rest was overly integrated in schizophrenic subjects. Both anomalies were correlated with the negative symptoms. These findings were consistent regardless of the task considered. Furthermore, within the core, anterior-posterior correlations were lower in patients (between the frontal and the parietal and posterior cingulate cortices), whereas frontal left-right correlations were excessive. No significant correlation was found with the medication. Thus, it appears that schizophrenia entails a deleterious combination of too much "noisy" integration (from the rest) and too little "significant" integration (anterior-posterior functional connectivity).

Adult↗

PubMed2004

P300 recordings during event-related fMRI: a feasibility study.

Analysis of combined event-related potentials (ERP) and functional magnetic resonance imaging (fMRI) can provide a high temporal and high spatial resolution to study functional cerebral processes. However, EEG data recorded inside an MR scanner is heavily distorted by artifacts. It is important in cognitive studies to ensure that recorded data reflect the same brain activity, and this is achieved through interleaved electroencephalographic (EEG) and fMRI measurements. Here, we demonstrate the feasibility of recording P300 ERPs during fMRI using a three-stimulus visual oddball task and involving a small number of trials for each stimulus. Ten EEG channels were acquired interleaved with fMRI images in five healthy subjects. The stimuli, including rare targets "X," frequent repetitive distractors "O," and rare distractors referred to as novels, were randomly presented every 2 +/- 1 s. The post hoc filter presented here was designed and applied to EEG data to remove the cardiac pulse artifact. Interleaved EEG/fMRI acquisition evidenced two P300 ERPs evoked at Fz, Cz, and Pz by targets and novels. Novel-related ERPs were of higher amplitude than their target-related counterparts. The fMRI maps acquired concurrently showed stronger BOLD response for target condition. We have shown that interleaved acquisition allows to obtain reliable P300 data and fMRI results, likely to shed light on the anatomical location of brain regions involved in cognitive ERPs relevant to many disorders affecting CNS functions. These noninvasive multimodal neuroimaging techniques can be used to explore and better understand processes underlying the functional brain organization.

Adolescent↗

PubMed2004

Where arousal meets attention: a simultaneous fMRI and EEG recording study.

In this fMRI study, we looked for the regions supporting interaction between cortical arousal and attention during three conditions: detection, observation, and rest. Arousal measurements were obtained from the EEG low-frequency (LF) power (5-9.5 Hz) recorded continuously together with fMRI. Whatever the condition, arousal was positively correlated with the fMRI signal of the right dorsal-lateral prefrontal and superior parietal cortices, closely overlapping regions involved in the maintenance of attention. Although the inferior temporal areas also presented a correlation with arousal during detection, path analysis suggests that this influence may be indirect, through the top-down influence of the previously mentioned network. However, those visual-processing areas could account for the correlation between arousal and performances. Lastly, the medial frontal cortex, frontal opercula, and thalamus were inversely correlated with arousal but only during detection and observation so that they could account for the control of arousal.

Adult↗

PubMed2001

Synchrony, from cognition to seizure.

It could seem strange that a same neuro-physiological mechanism provides for both normal and critical cerebral activity. While describing the basics of "cognitive" synchronies we will contrast them with the "critical" one for their differentiation and their non-rhythmic properties. Lastly we will speculate on their significance in the recently described seizure anticipation paradigm and on the possibility that they could share common generators.

Journal Article↗