Publications by authors named "Phetsamone Vannasing"

39 Publications

Differential auditory brain response abnormalities in two intellectual disability conditions: SYNGAP1 mutations and Down syndrome.

Clin Neurophysiol 2021 Aug 13;132(8):1802-1812. Epub 2021 May 13.

Department of Psychology, University of Montreal, Montreal, Québec, Canada; CHU Sainte-Justine Research Center, Montreal, Quebec, Canada. Electronic address:

Objective: Altered sensory processing is common in intellectual disability (ID). Here, we study electroencephalographic responses to auditory stimulation in human subjects presenting a rare condition (mutations in SYNGAP1) which causes ID, epilepsy and autism.

Methods: Auditory evoked potentials, time-frequency and inter-trial coherence analyses were used to compare subjects with SYNGAP1 mutations with Down syndrome (DS) and neurotypical (NT) participants (N = 61 ranging from three to 19 years of age).

Results: Altered synchronization in the brain responses to sound were found in both ID groups. The SYNGAP1 mutations group showed less phase-locking in early time windows and lower frequency bands compared to NT, and in later time windows compared to NT and DS. Time-frequency analysis showed more power in beta-gamma in the SYNGAP1 group compared to NT participants.

Conclusions: This study indicated reduced synchronization as well as more high frequencies power in SYNGAP1 mutations, while maintained synchronization was found in the DS group. These results might reflect dysfunctional sensory information processing caused by excitation/inhibition imbalance, or an imperfect compensatory mechanism in SYNGAP1 mutations individuals.

Significance: Our study is the first to reveal brain response abnormalities in auditory sensory processing in SYNGAP1 mutations individuals, that are distinct from DS, another ID condition.
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http://dx.doi.org/10.1016/j.clinph.2021.03.054DOI Listing
August 2021

Distinct patterns of repetition suppression in Fragile X syndrome, down syndrome, tuberous sclerosis complex and mutations in SYNGAP1.

Brain Res 2021 01 12;1751:147205. Epub 2020 Nov 12.

Psychology Departement, Université de Montréal, Pavillon Marie-Victorin, 90, Avenue Vincent d'Indy, Montréal, QC H2V 2S9, Canada; NED Laboratory, Office 5.2.43, 3175 Chemin de la Côte-Sainte-Catherine, Montréal, QC H3T 1C5, Canada; Research Center UHC Sainte-Justine, 3175 Chemin de la Côte-Sainte-Catherine, Montréal, QC H3T 1C5, Canada. Electronic address:

Sensory processing is the gateway to information processing and more complex processes such as learning. Alterations in sensory processing is a common phenotype of many genetic syndromes associated with intellectual disability (ID). It is currently unknown whether sensory processing alterations converge or diverge on brain responses between syndromes. Here, we compare for the first time four genetic conditions with ID using the same basic sensory learning paradigm. One hundred and five participants, aged between 3 and 30 years old, composing four clinical ID groups and one control group, were recruited: Fragile X syndrome (FXS; n = 14), tuberous sclerosis complex (TSC; n = 9), Down syndrome (DS; n = 19), SYNGAP1 mutations (n = 8) and Neurotypical controls (NT; n = 55)). All groups included female and male participants. Brain responses were recorded using electroencephalography (EEG) during an audio-visual task that involved three repetitions of the pronunciation of the phoneme /a/. Event Related Potentials (ERP) were used to: 1) compare peak-to-peak amplitudes between groups, 2) evaluate the presence of repetition suppression within each group and 3) compare the relative repetition suppression between groups. Our results revealed larger overall amplitudes in FXS. A repetition suppression (RS) pattern was found in the NT group, FXS and DS, suggesting spared repetition suppression in a multimodal task in these two ID syndromes. Interestingly, FXS presented a stronger RS on one peak-to-peak value in comparison with the NT. The results of our study reveal the distinctiveness of ERP and RS brain responses in ID syndromes. Further studies should be conducted to understand the molecular mechanisms involved in these patterns of responses.
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http://dx.doi.org/10.1016/j.brainres.2020.147205DOI Listing
January 2021

Functional Brain Connectivity of Language Functions in Children Revealed by EEG and MEG: A Systematic Review.

Front Hum Neurosci 2020 12;14:62. Epub 2020 Mar 12.

Laboratoire d'imagerie optique en neurodéveloppement (LIONLAB), Sainte-Justine University Hospital Research Center, Montréal, QC, Canada.

The development of language functions is of great interest to neuroscientists, as these functions are among the fundamental capacities of human cognition. For many years, researchers aimed at identifying cerebral correlates of language abilities. More recently, the development of new data analysis tools has generated a shift toward the investigation of complex cerebral networks. In 2015, Weiss-Croft and Baldeweg published a very interesting systematic review on the development of functional language networks, explored through the use of functional magnetic resonance imaging (fMRI). Compared to fMRI and because of their excellent temporal resolution, magnetoencephalography (MEG) and electroencephalography (EEG) provide different and important information on brain activity. Both therefore constitute crucial neuroimaging techniques for the investigation of the maturation of functional language brain networks. The main objective of this systematic review is to provide a state of knowledge on the investigation of language-related cerebral networks in children, through the use of EEG and MEG, as well as a detailed portrait of relevant MEG and EEG data analysis methods used in that specific research context. To do so, we have summarized the results and systematically compared the methodological approach of 24 peer-reviewed EEG or MEG scientific studies that included healthy children and children with or at high risk of language disabilities, from birth up to 18 years of age. All included studies employed functional and effective connectivity measures, such as coherence, phase locking value, and Phase Slope Index, and did so using different experimental paradigms (e.g., at rest or during language-related tasks). This review will provide more insight into the use of EEG and MEG for the study of language networks in children, contribute to the current state of knowledge on the developmental path of functional connectivity in language networks during childhood and adolescence, and finally allow future studies to choose the most appropriate type of connectivity analysis.
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http://dx.doi.org/10.3389/fnhum.2020.00062DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7080982PMC
March 2020

Comparison of source localization techniques in diffuse optical tomography for fNIRS application using a realistic head model.

Biomed Opt Express 2018 Jul 7;9(7):2994-3016. Epub 2018 Jun 7.

LIONLAB, Centre de recherche du CHU Sainte-Justine, Université de Montréal, Montréal, Canada.

Functional near-infrared spectroscopy (fNIRS) is a non-invasive imaging technique that elicits growing interest for research and clinical applications. In the last decade, efforts have been made to develop a mathematical framework in order to image the effective sources of hemoglobin variations in brain tissues. Different approaches can be used to impose additional information or constraints when reconstructing the cerebral images of an ill-posed problem. The goal of this study is to compare the performance and limitations of several source localization techniques in the context of fNIRS tomography using individual anatomical magnetic resonance imaging (MRI) to model light propagation. The forward problem is solved using a Monte Carlo simulation of light propagation in the tissues. The inverse problem has been linearized using the Rytov approximation. Then, Tikhonov regularization applied to least squares, truncated singular value decomposition, back-projection, L1-norm regularization, minimum norm estimates, low resolution electromagnetic tomography and Bayesian model averaging techniques are compared using a receiver operating characteristic analysis, blurring and localization error measures. Using realistic simulations (n = 450) and data acquired from a human participant, this study depicts how these source localization techniques behave in a human head fNIRS tomography. When compared to other methods, Bayesian model averaging is proposed as a promising method in DOT and shows great potential to improve specificity, accuracy, as well as to reduce blurring and localization error even in presence of noise and deep sources. Classical reconstruction methods, such as regularized least squares, offer better sensitivity but higher blurring; while more novel L1-based method provides sparse solutions with small blurring and high specificity but lower sensitivity. The application of these methods is also demonstrated experimentally using visual fNIRS experiment with adult participant.
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http://dx.doi.org/10.1364/BOE.9.002994DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6033567PMC
July 2018

Auditory repetition suppression alterations in relation to cognitive functioning in fragile X syndrome: a combined EEG and machine learning approach.

J Neurodev Disord 2018 01 29;10(1). Epub 2018 Jan 29.

Neuroscience of Early Development (NED), 90 Avenue Vincent-D'indy, Montreal, QC, H2V 2S9, Canada.

Background: Fragile X syndrome (FXS) is a neurodevelopmental genetic disorder causing cognitive and behavioural deficits. Repetition suppression (RS), a learning phenomenon in which stimulus repetitions result in diminished brain activity, has been found to be impaired in FXS. Alterations in RS have been associated with behavioural problems in FXS; however, relations between RS and intellectual functioning have not yet been elucidated.

Methods: EEG was recorded in 14 FXS participants and 25 neurotypical controls during an auditory habituation paradigm using repeatedly presented pseudowords. Non-phased locked signal energy was compared across presentations and between groups using linear mixed models (LMMs) in order to investigate RS effects across repetitions and brain areas and a possible relation to non-verbal IQ (NVIQ) in FXS. In addition, we explored group differences according to NVIQ and we probed the feasibility of training a support vector machine to predict cognitive functioning levels across FXS participants based on single-trial RS features.

Results: LMM analyses showed that repetition effects differ between groups (FXS vs. controls) as well as with respect to NVIQ in FXS. When exploring group differences in RS patterns, we found that neurotypical controls revealed the expected pattern of RS between the first and second presentations of a pseudoword. More importantly, while FXS participants in the ≤ 42 NVIQ group showed no RS, the > 42 NVIQ group showed a delayed RS response after several presentations. Concordantly, single-trial estimates of repetition effects over the first four repetitions provided the highest decoding accuracies in the classification between the FXS participant groups.

Conclusion: Electrophysiological measures of repetition effects provide a non-invasive and unbiased measure of brain responses sensitive to cognitive functioning levels, which may be useful for clinical trials in FXS.
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http://dx.doi.org/10.1186/s11689-018-9223-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5789548PMC
January 2018

Multichannel wearable fNIRS-EEG system for long-term clinical monitoring.

Hum Brain Mapp 2018 01 23;39(1):7-23. Epub 2017 Oct 23.

Research Center, Centre Hospitalier Universitaire de Montréal, Université de Montréal, Montréal, Québec, H2X 0A9, Canada.

Continuous brain imaging techniques can be beneficial for the monitoring of neurological pathologies (such as epilepsy or stroke) and neuroimaging protocols involving movement. Among existing ones, functional near-infrared spectroscopy (fNIRS) and electroencephalography (EEG) have the advantage of being noninvasive, nonobstructive, inexpensive, yield portable solutions, and offer complementary monitoring of electrical and local hemodynamic activities. This article presents a novel system with 128 fNIRS channels and 32 EEG channels with the potential to cover a larger fraction of the adult superficial cortex than earlier works, is integrated with 32 EEG channels, is light and battery-powered to improve portability, and can transmit data wirelessly to an interface for real-time display of electrical and hemodynamic activities. A novel fNIRS-EEG stretchable cap, two analog channels for auxiliary data (e.g., electrocardiogram), eight digital triggers for event-related protocols and an internal accelerometer for movement artifacts removal contribute to improve data acquisition quality. The system can run continuously for 24 h. Following instrumentation validation and reliability on a solid phantom, performance was evaluated on (1) 12 healthy participants during either a visual (checkerboard) task at rest or while pedalling on a stationary bicycle or a cognitive (language) task and (2) 4 patients admitted either to the epilepsy (n = 3) or stroke (n = 1) units. Data analysis confirmed expected hemodynamic variations during validation recordings and useful clinical information during in-hospital testing. To the best of our knowledge, this is the first demonstration of a wearable wireless multichannel fNIRS-EEG monitoring system in patients with neurological conditions. Hum Brain Mapp 39:7-23, 2018. © 2017 Wiley Periodicals, Inc.
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http://dx.doi.org/10.1002/hbm.23849DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6866376PMC
January 2018

Altered visual repetition suppression in Fragile X Syndrome: New evidence from ERPs and oscillatory activity.

Int J Dev Neurosci 2017 Jun 19;59:52-59. Epub 2017 Mar 19.

Departement de Psychologie, Université de Montréal, Montreal, Canada; Neuroscience of Early Development (NED), Montreal, Canada; Centre de Recherche en Neuropsychologie et Cognition (CERNEC), Montreal, Canada; Research Center of the CHU Ste-Justine Mother and Child University Hospital Center, Université de Montreal, Quebec, Canada; International Laboratory for Brain, Music and Sound Research (BRAMS), Montreal, Quebec, Canada.

Fragile X Syndrome (FXS) is a neurodevelopmental genetic disorder associated with cognitive and behavioural deficits. In particular, neuronal habituation processes have been shown to be altered in FXS patients. Yet, while such deficits have been primarily explored using auditory stimuli, less is known in the visual modality. Here, we investigated the putative alteration of repetition suppression using faces in FXS patients compared to controls that had the same age distribution. Electroencephalographic (EEG) signals were acquired while participants were presented with 18 different faces, each repeated ten times successively. The repetition suppression effect was probed by comparing the brain responses to the first and second presentation, based on task-evoked event-related potentials (ERP) as well as on task-induced oscillatory activity. We found different patterns of habituation for controls and patients both in ERP and oscillatory power. While the N170 was not affected by face repetition in controls, it was altered in FXS patients. Conversely, while a repetition suppression effect was observed in the theta band (4-8Hz) over frontal and parieto-occipital areas in controls, it was not seen in FXS patients. These results provide the first evidence for diminished ERP and oscillatory habituation effects in response to face repetitions in FXS. These findings extend previous observations of impairments in learning mechanisms and may be linked to deficits in the maturation processes of synapses caused by the mutation. The present study contributes to bridging the gap between animal models of synaptic plasticity dysfunctions and human research in FXS.
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http://dx.doi.org/10.1016/j.ijdevneu.2017.03.008DOI Listing
June 2017

Language mapping in children using resting-state functional connectivity: comparison with a task-based approach.

J Biomed Opt 2016 12;21(12):125006

CHU Sainte-Justine Research Center, Laboratoire d'Imagerie Optique en Neurodéveloppement (LIONLab), 3175 Chemin de la Côte-Sainte-Catherine, Montréal, Québec H3T 1C5, CanadabUniversité de Montréal, Centre de Recherche en Neuropsychologie et Cognition, Department of Psychology, Marie-Victorin Building, P.O. Box 6128 Centre-ville Station, 2900 Boulevard Édouard-Montpetit, Montréal, Québec H3T 1J4, Canada.

Patients with brain tumor or refractory epilepsy may be candidates for neurosurgery. Presurgical evaluation often includes language investigation to prevent or reduce the risk of postsurgical language deficits. Current techniques involve significant limitations with pediatric populations. Recently, near-infrared spectroscopy (NIRS) has been shown to be a valuable neuroimaging technique for language localization in children. However, it typically requires the child to perform a task (task-based NIRS), which may constitute a significant limitation. Resting-state functional connectivity NIRS (fcNIRS) is an approach that can be used to identify language networks at rest. This study aims to assess the utility of fcNIRS in children by comparing fcNIRS to more conventional task-based NIRS for language mapping in 33 healthy participants: 25 children (ages 3 to 16) and 8 adults. Data were acquired at rest and during a language task. Results show very good concordance between both approaches for language localization (Dice similarity coefficient = 0.81 ± 0.13 ) and hemispheric language dominance ( kappa = 0.86 , p < 0.006 ). The fcNIRS technique may be a valuable tool for language mapping in clinical populations, including children and patients with cognitive and behavioral impairments.
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http://dx.doi.org/10.1117/1.JBO.21.12.125006DOI Listing
December 2016

Electrophysiological correlates of emotional face processing after mild traumatic brain injury in preschool children.

Cogn Affect Behav Neurosci 2017 02;17(1):124-142

Département de Psychologie, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, Canada, H3C 3J7.

Evidence suggests that social skills are affected by childhood mild traumatic brain injury (mTBI), but the neural and affective substrates of these difficulties are still underexplored. In particular, nothing is known about consequences on the perception of emotional facial expressions, despite its critical role in social interactions and the importance of the preschool period in the development of this ability. This study thus aimed to investigate the electrophysiological correlates of emotional facial expressions processing after early mTBI. To this end, 18 preschool children (mean age 53 ± 8 months) who sustained mTBI and 15 matched healthy controls (mean age 55 ± 11 months) were presented with pictures of faces expressing anger, happiness, or no emotion (neutral) while event-related potentials (ERP) were recorded. The main results revealed that P1 amplitude was higher for happy faces than for angry faces, and that N170 latency was shorter for emotional faces than for neutral faces in the control group only. These findings suggest that preschool children who sustain mTBI do not present the early emotional effects that are observed in healthy preschool children at visuospatial and visual expertise stages. This study provides new evidence regarding the consequences of childhood mTBI on socioemotional processing, by showing alterations of emotional facial expressions processing, an ability known to underlie social competence and appropriate social interactions.
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http://dx.doi.org/10.3758/s13415-016-0467-7DOI Listing
February 2017

Potential brain language reorganization in a boy with refractory epilepsy; an fNIRS-EEG and fMRI comparison.

Epilepsy Behav Case Rep 2016 9;5:34-7. Epub 2016 Feb 9.

CHU Sainte-Justine Research Center, Montreal, Quebec, Canada; Psychology Department, Centre de Recherche de Neuropsychologie et Cognition (CERNEC), Université de Montréal, Quebec, Canada.

As part of a presurgical investigation for a resection of a tumor located in the left temporal brain region, we evaluated pre- and postsurgical language lateralization in a right-handed boy with refractory epilepsy. In this study, we compared functional near infrared spectroscopy (fNIRS) results obtained while the participant performed expressive and receptive language tasks with those obtained using functional magnetic resonance imaging (fMRI). This case study illustrates the potential for NIRS to contribute favorably to the localization of language functions in children with epilepsy and cognitive or behavioral problems and its potential advantages over fMRI in presurgical assessment. Moreover, it suggests that fNIRS is sensitive in localizing an atypical language network or potential brain reorganization related to epilepsy in young patients.
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http://dx.doi.org/10.1016/j.ebcr.2016.01.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4782003PMC
March 2016

Recruitment of the left precentral gyrus in reading epilepsy: A multimodal neuroimaging study.

Epilepsy Behav Case Rep 2016 21;5:19-22. Epub 2016 Jan 21.

Centre de Recherche du CHU Sainte-Justine, Montréal, Canada; Département de Psychologie, Université de Montréal, Montréal, Canada.

Purpose: In a previous study, we investigated a 42-year-old male patient with primary reading epilepsy using continuous video-electroencephalography (EEG). Reading tasks induced left parasagittal spikes with a higher spike frequency when the phonological reading pathway was recruited compared to the lexical one. Here, we seek to localize the epileptogenic focus in the same patient as a function of reading pathway using multimodal neuroimaging.

Methods And Results: The participant read irregular words and nonwords presented in a block-design paradigm during magnetoencephalography (MEG), functional near-infrared spectroscopy (fNIRS), and functional magnetic resonance imaging (fMRI) recordings, all combined with EEG. Spike analyses from MEG, fNIRS, and fMRI-EEGs data revealed an epileptic focus in the left precentral gyrus, and spike localization did not differ in lexical and phonological reading.

Conclusion: This study is the first to investigate ictogenesis in reading epilepsy during both lexical and phonological reading while using three different multimodal neuroimaging techniques. The somatosensory and motor control functions of the left precentral gyrus that are congruently involved in lexical as well as phonological reading can explain the identical spike localization in both reading pathways. The concurrence between our findings in this study and those from our previous one supports the role of the left precentral gyrus in phonological output computation as well as seizure activity in a case of reading epilepsy.
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http://dx.doi.org/10.1016/j.ebcr.2016.01.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4744333PMC
February 2016

Distinct hemispheric specializations for native and non-native languages in one-day-old newborns identified by fNIRS.

Neuropsychologia 2016 Apr 4;84:63-9. Epub 2016 Feb 4.

Sainte-Justine University Hospital Research Centre, 3175, Chemin de la Côte-Sainte-Catherine, Montréal H3T 1C5, QC, Canada; Centre de Recherche en Neuropsychologie et Cognition (CERNEC), Université de Montréal, CP 6128, succursale Centre-Ville, Montréal H3C 3J7, QC, Canada. Electronic address:

This study assessed whether the neonatal brain recruits different neural networks for native and non-native languages at birth. Twenty-seven one-day-old full-term infants underwent functional near-infrared spectroscopy (fNIRS) recording during linguistic and non-linguistic stimulation. Fourteen newborns listened to linguistic stimuli (native and non-native language stories) and 13 newborns were exposed to non-linguistic conditions (native and non-native stimuli played in reverse). Comparisons between left and right hemisphere oxyhemoglobin (HbO2) concentration changes over the temporal areas revealed clear left hemisphere dominance for native language, whereas non-native stimuli were associated with right hemisphere lateralization. In addition, bilateral cerebral activation was found for non-linguistic stimulus processing. Overall, our findings indicate that from the first day after birth, native language and prosodic features are processed in parallel by distinct neural networks.
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http://dx.doi.org/10.1016/j.neuropsychologia.2016.01.038DOI Listing
April 2016

Using patient-specific hemodynamic response function in epileptic spike analysis of human epilepsy: a study based on EEG-fNIRS.

Neuroimage 2016 Feb 24;126:239-55. Epub 2015 Nov 24.

Département de génie électrique, Institut de génie biomédical, École Polytechnique de Montréal, C.P.6079, Succ. Centre-ville, Montréal, QC H3C3A7, Canada; Institut de cardiologie de Montréal, Centre de recherche, 5000 Rue Bélanger Est, Montréal, QC H1T1C8, Canada. Electronic address:

Functional near-infrared spectroscopy (fNIRS) can be combined with electroencephalography (EEG) to continuously monitor the hemodynamic signal evoked by epileptic events such as seizures or interictal epileptiform discharges (IEDs, aka spikes). As estimation methods assuming a canonical shape of the hemodynamic response function (HRF) might not be optimal, we sought to model patient-specific HRF (sHRF) with a simple deconvolution approach for IED-related analysis with EEG-fNIRS data. Furthermore, a quadratic term was added to the model to account for the nonlinearity in the response when IEDs are frequent. Prior to analyzing clinical data, simulations were carried out to show that the HRF was estimable by the proposed deconvolution methods under proper conditions. EEG-fNIRS data of five patients with refractory focal epilepsy were selected due to the presence of frequent clear IEDs and their unambiguous focus localization. For each patient, both the linear sHRF and the nonlinear sHRF were estimated at each channel. Variability of the estimated sHRFs was seen across brain regions and different patients. Compared with the SPM8 canonical HRF (cHRF), including these sHRFs in the general linear model (GLM) analysis led to hemoglobin activations with higher statistical scores as well as larger spatial extents on all five patients. In particular, for patients with frequent IEDs, nonlinear sHRFs were seen to provide higher sensitivity in activation detection than linear sHRFs. These observations support using sHRFs in the analysis of IEDs with EEG-fNIRS data.
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http://dx.doi.org/10.1016/j.neuroimage.2015.11.045DOI Listing
February 2016

Early electrophysiological markers of atypical language processing in prematurely born infants.

Neuropsychologia 2015 Dec 22;79(Pt A):21-32. Epub 2015 Oct 22.

Sainte-Justine University Hospital Research Center, Montreal, QC, Canada; Centre de Recherche en Neuropsychologie et Cognition, University of Montreal, Montreal, QC, Canada. Electronic address:

Because nervous system development may be affected by prematurity, many prematurely born children present language or cognitive disorders at school age. The goal of this study is to investigate whether these impairments can be identified early in life using electrophysiological auditory event-related potentials (AERPs) and mismatch negativity (MMN). Brain responses to speech and non-speech stimuli were assessed in prematurely born children to identify early electrophysiological markers of language and cognitive impairments. Participants were 74 children (41 full-term, 33 preterm) aged 3, 12, and 36 months. Pre-attentional auditory responses (MMN and AERPs) were assessed using an oddball paradigm, with speech and non-speech stimuli presented in counterbalanced order between participants. Language and cognitive development were assessed using the Bayley Scale of Infant Development, Third Edition (BSID-III). Results show that preterms as young as 3 months old had delayed MMN response to speech stimuli compared to full-terms. A significant negative correlation was also found between MMN latency to speech sounds and the BSID-III expressive language subscale. However, no significant differences between full-terms and preterms were found for the MMN to non-speech stimuli, suggesting preserved pre-attentional auditory discrimination abilities in these children. Identification of early electrophysiological markers for delayed language development could facilitate timely interventions.
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http://dx.doi.org/10.1016/j.neuropsychologia.2015.10.021DOI Listing
December 2015

Early childhood development of visual texture segregation in full-term and preterm children.

Vision Res 2015 Jul 12;112:1-10. Epub 2015 May 12.

Research Centre in Neuropsychology and Cognition, University of Montreal, Quebec, Canada; Department of Psychology, University of Montreal, Quebec, Canada; Research Centre, Sainte-Justine Hospital, Montreal, Quebec, Canada. Electronic address:

To date, very little is known about the normal development trajectory of visual texture segregation, or how it is affected by preterm birth. The goal of this study was to characterize the development of visual texture segregation using texture segregation visual evoked potentials (tsVEPs) in children born full-term and children born preterm without major neurological impairment. Forty-five full-term and 43 preterm children were tested at either 12, 24 or 36 months of age (corrected age for prematurity at 12 and 24 months old). VEPs were obtained using two lower-level stimuli defined by orientation (oriVEP) and two higher-level stimuli defined by texture (texVEP). TsVEP was obtained by dividing by two the subtraction of oriVEP from texVEP. Results show a clear maturation of the processes underlying visual texture segregation in the full-term group, with a significant N2 latency reduction between 12 and 36 months of age for all conditions. Significant N2 amplitude reduction was observed for oriVEP between 12 and 24 months, as well as for texVEP between 12 and 24 months, and 12 and 36 months. Comparison between full-term and preterm children indicated significantly lower N2 amplitude for the preterm group at 12 months for oriVEP and texVEP. These differences were no longer apparent at 24 months of age, suggesting that children born preterm catch up with their full-term counterparts somewhere between 12 and 24 months of age. Our results appear to reflect a maturational delay in preterm children in both lower-level and higher-level visual processing during, at least, early childhood.
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http://dx.doi.org/10.1016/j.visres.2015.04.013DOI Listing
July 2015

Developmental patterns of expressive language hemispheric lateralization in children, adolescents and adults using functional near-infrared spectroscopy.

Neuropsychologia 2015 Feb 8;68:117-25. Epub 2015 Jan 8.

Sainte-Justine University Hospital Research Center, 3175 Chemin de la Côte-Sainte-Catherine, Montréal, QC, Canada H3T 1C5; Centre de Recherche en Neuropsychologie et Cognition, Université de Montréal, P.O. Box 6128, Downtown Station, Montreal, QC, Canada H3C 3J7. Electronic address:

The development of language hemispheric specialization is not well understood in young children, especially regarding expressive language functions. In this study, we investigated age-related changes in expressive language lateralization patterns in a population of children (3-6 and 7-10 years old), adolescents (11-16 years old), and young adults (19-30 years old). During functional near-infrared spectroscopy recordings, all participants performed a verbal fluency task, which consisted in naming as many words as possible belonging to a given semantic category. Hemoglobin concentration changes were measured in bilateral frontal and temporal cortical areas. During the language task, results showed a strong left hemisphere response along with weaker right hemisphere activation in all groups. Age-related increases in hemodynamic responses were found bilaterally, with younger children showing smaller hemodynamic responses than adolescents and adults in both hemispheres. Overall, these findings confirm that a left hemisphere specialization is already established in young children and persists through adulthood. Early left hemisphere specialization for expressive language suggests that language development hinges on structural and functional properties of the human brain with little reorganization occurring with development.
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http://dx.doi.org/10.1016/j.neuropsychologia.2015.01.007DOI Listing
February 2015

Visual Development and Neuropsychological Profile in Preterm Children from 6 Months to School Age.

J Child Neurol 2015 Aug 20;30(9):1159-73. Epub 2014 Nov 20.

Research Centre in Neuropsychology and Cognition, University of Montreal, Quebec, Canada Department of Psychology, University of Montreal, Quebec, Canada Research Centre, Sainte-Justine Hospital, Montreal, Quebec, Canada

The aim of this semilongitudinal study was to investigate the development of central visual pathways in children born preterm but without major neurologic impairments and to establish their cognitive and behavioral profile at school age. Ten children born preterm were assessed at 6 months and at school age, using visual evoked potentials at both time points and cognitive and behavioral tests at school age. We also tested 10 age-matched children born full-term. At 6 months' corrected age, we found no significant differences between preterm and full-term groups for either amplitude or latency of N1 and P1 components. At school age, the preterm group manifested significantly higher N1 amplitudes and tended to show higher P1 amplitudes than the full-term group. We found no significant differences in cognitive and behavioral measures at school age. These results suggest that preterm birth affects visual pathways development, yet the children born preterm did not manifest cognitive problems.
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http://dx.doi.org/10.1177/0883073814555188DOI Listing
August 2015

Delayed early primary visual pathway development in premature infants: high density electrophysiological evidence.

PLoS One 2014 30;9(9):e107992. Epub 2014 Sep 30.

Centre de Recherche, Centre Hospitalier Universitaire Ste-Justine, Montréal, Québec, Canada; Centre de Recherche en Neuropsychologie et Cognition, Département de Psychologie, Université de Montréal, Montréal, Québec, Canada.

In the past decades, multiple studies have been interested in developmental patterns of the visual system in healthy infants. During the first year of life, differential maturational changes have been observed between the Magnocellular (P) and the Parvocellular (P) visual pathways. However, few studies investigated P and M system development in infants born prematurely. The aim of the present study was to characterize P and M system maturational differences between healthy preterm and fullterm infants through a critical period of visual maturation: the first year of life. Using a cross-sectional design, high-density electroencephalogram (EEG) was recorded in 31 healthy preterms and 41 fullterm infants of 3, 6, or 12 months (corrected age for premature babies). Three visual stimulations varying in contrast and spatial frequency were presented to stimulate preferentially the M pathway, the P pathway, or both systems simultaneously during EEG recordings. Results from early visual evoked potentials in response to the stimulation that activates simultaneously both systems revealed longer N1 latencies and smaller P1 amplitudes in preterm infants compared to fullterms. Moreover, preterms showed longer N1 and P1 latencies in response to stimuli assessing the M pathway at 3 months. No differences between preterms and fullterms were found when using the preferential P system stimulation. In order to identify the cerebral generator of each visual response, distributed source analyses were computed in 12-month-old infants using LORETA. Source analysis demonstrated an activation of the parietal dorsal region in fullterm infants, in response to the preferential M pathway, which was not seen in the preterms. Overall, these findings suggest that the Magnocellular pathway development is affected in premature infants. Although our VEP results suggest that premature children overcome, at least partially, the visual developmental delay with time, source analyses reveal abnormal brain activation of the Magnocellular pathway at 12 months of age.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0107992PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4182425PMC
June 2015

Spatiotemporal dynamics of affective picture processing revealed by intracranial high-gamma modulations.

Hum Brain Mapp 2015 Jan 21;36(1):16-28. Epub 2014 Aug 21.

Centre de Recherche en Neuropsychologie et Cognition, Département de psychologie, Université de Montréal, Montréal, Quebec, Canada; Centre de recherche de l'Hôpital Sainte-Justine, Hôpital Sainte-Justine, Montréal, Quebec, Canada.

Our comprehension of the neural mechanisms underlying emotional information processing has largely benefited from noninvasive electrophysiological and functional neuroimaging techniques in recent years. However, the spatiotemporal dynamics of the neural events occurring during emotional processing remain imprecise due to the limited combination of spatial and temporal resolution provided by these techniques. This study examines the modulations of high-frequency activity of intracranial electroencephalography recordings associated with affective picture valence, in epileptic patients awaiting neurosurgery. Recordings were obtained from subdural grids and depth electrodes in eight patients while they viewed a series of unpleasant, pleasant and neutral pictures from the International Affective Picture System. Broadband high-gamma (70-150 Hz) power was computed for separate 100-ms time windows and compared according to ratings of emotional valence. Compared to emotionally neutral or pleasant pictures, unpleasant stimuli were associated with an early and long-lasting (≈200-1,000 ms) bilateral increase in high-gamma activity in visual areas of the occipital and temporal lobes, together with a late and transient (≈500-800 ms) decrease found bilaterally in the lateral prefrontal cortex (PFC). Pleasant pictures were associated with increased gamma activity in the occipital cortex, compared to the emotionally neutral stimuli. Consistent with previous studies, our results provide direct evidence of emotion-related modulations in the visual ventral pathway during picture processing. Results in the lateral PFC also shed light on the neural mechanisms underlying its role in negative emotions processing. This study demonstrates the utility of intracranial high-gamma modulations to study emotional process with a high spatiotemporal precision.
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http://dx.doi.org/10.1002/hbm.22609DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6869418PMC
January 2015

Alterations of visual and auditory evoked potentials in fragile X syndrome.

Int J Dev Neurosci 2014 Aug 27;36:90-7. Epub 2014 May 27.

Research Center of the CHU Ste-Justine Mother and Child University Hospital Center, University of Montreal, Quebec, Canada; Psychology Department, University of Montreal, Quebec, Canada; Centre de Recherche en Neuropsychologie et Cognition, University of Montreal, Quebec, Canada.

Background: Fragile X Syndrome (FXS) is the most common monogenic form of intellectual disability and one of the few known monogenic causes of autism. It is caused by a trinucleotide repeat expansion in the FMR1 ('Fragile X Mental Retardation 1') gene, which prevents expression of the 'Fragile X Mental Retardation Protein' (FMRP). In FXS, the absence of FMRP leads to altered structural and functional development of the synapse, while preventing activity-based synapse maturation and synaptic pruning, which are essential for normal brain development and cognitive development. Possible impairments in information processing can be non-invasively investigated using electrophysiology.

Methods: We compared auditory (AEP) and visual (VEP) evoked potentials in twelve adolescents and young adults (10-22 years) affected by FXS to healthy controls matched by chronological age (N=12) and developmental age of cognitive functioning (N=9; 5-7 years), using analysis of variance.

Results: In the visual modality, the N70 and N2 amplitude have been found increased in FXS in comparison to the chronological, but not the developmental control group at occipital sites, whereas in the auditory modality N1, P2 and N2 amplitude as well as N2 latency have been found increased in FXS, relative to both chronological and developmental control groups at mid-central sites.

Conclusions: The AEP/VEP profile suggests disruptions in sensory processing specific to FXS that exceed immaturity of physiological activity. In addition, the auditory modality seems to be more affected than the visual modality. Results are discussed in light of possible underlying neuronal mechanisms, including deficits in synaptic pruning and neuronal inhibition that might account for a hyperreactive nervous system in FXS.
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http://dx.doi.org/10.1016/j.ijdevneu.2014.05.003DOI Listing
August 2014

Hemodynamic changes during posterior epilepsies: an EEG-fNIRS study.

Epilepsy Res 2014 Jul 26;108(5):883-90. Epub 2014 Mar 26.

Service de neurologie, Hôpital Notre-Dame du CHUM, 1560 Rue Sherbrooke Est, Montréal, QC, Canada H3L4M1.

Posterior epilepsies are mainly characterized clinically by visual symptoms. Functional near-infrared spectroscopy (fNIRS) is an emerging non-invasive imaging technique that has the potential to monitor hemodynamic changes during epileptic activity. Combined with electroencephalography (EEG), 9 patients with posterior epilepsies were recorded using EEG-fNIRS with large sampling (19 EEG electrodes and over 100 fNIRS channels). Spikes and seizures were carefully marked on EEG traces, and convolved with a standard hemodynamic response function for general linear model (GLM) analysis. GLM results for seizures (in 3 patients) and spikes (7 patients) were broadly sensitive to the epileptic focus in 7/9 patients, and specific in 5/9 patients with fNIRS deoxyhemoglobin responses lateralized to the correct lobe, and to plausible locations within the occipital or parietal lobes. This work provides evidence that EEG-fNIRS is a sensitive technique for monitoring posterior epileptic activity.
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http://dx.doi.org/10.1016/j.eplepsyres.2014.03.007DOI Listing
July 2014

Recognizing an object from the sum of its parts: an intracranial study on alpha rhythms.

J Cogn Neurosci 2014 Aug 23;26(8):1797-805. Epub 2014 Jan 23.

Université de Montréal.

Little is known about the relation of alpha rhythms and object recognition. Alpha has been generally proposed to be associated with attention and memory and to be particularly important for the mediation of long-distance communication between neuronal populations. However, how these apply to object recognition is still unclear. This study aimed at describing the spatiotemporal dynamics of alpha rhythms while recognizing fragmented images of objects presented for the first time and presented again 24 hr later. Intracranial electroencephalography was performed in six epileptic patients undergoing presurgical evaluation. Time-frequency analysis revealed a strong alpha activity, mainly of the evoked type, propagating from posterior cerebral areas to anterior regions, which was similar whether the objects were recognized or not. Phase coherence analysis, however, showed clear phase synchronization specific for the moment of recognition. Twenty-four hr later, frontal regions displayed stronger alpha activity and more distributed phase synchronization than when images were presented for the first time. In conclusion, alpha amplitude seems to be related to nonspecific mechanism. Phase coherence analysis suggests a communicational role of alpha activity in object recognition, which may be important for the comparison between bottom-up representations and memory templates.
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http://dx.doi.org/10.1162/jocn_a_00582DOI Listing
August 2014

fNIRS-EEG study of focal interictal epileptiform discharges.

Epilepsy Res 2014 Mar 30;108(3):491-505. Epub 2013 Dec 30.

Département de génie électrique, École Polytechnique de Montréal, C.P. 6079, Succ. Centre-ville, Montréal, QC, Canada H3C3A7; Institut de cardiologie de Montréal, Centre de recherche, 5000 Rue Bélanger Est, Montréal, QC, Canada H1T1C8. Electronic address:

Functional near-infrared spectroscopy (fNIRS) acquired with electroencephalography (EEG) is a relatively new non-invasive neuroimaging technique with potential for long term monitoring of the epileptic brain. Simultaneous EEG-fNIRS recording allows the spatio-temporal reconstruction of the hemodynamic response in terms of the concentration changes in oxy-hemoglobin (HbO) and deoxy-hemoglobin (HbR) associated with recorded epileptic events such as interictal epileptic discharges (IEDs) or seizures. While most previous studies investigating fNIRS in epilepsy had limitations due to restricted spatial coverage and small sample sizes, this work includes a sufficiently large number of channels to provide an extensive bilateral coverage of the surface of the brain for a sample size of 40 patients with focal epilepsies. Topographic maps of significant activations due to each IED type were generated in four different views (dorsal, frontal, left and right) and were compared with the epileptic focus previously identified by an epileptologist. After excluding 5 patients due to the absence of IEDs and 6 more with mesial temporal foci too deep for fNIRS, we report that significant HbR (respectively HbO) concentration changes corresponding to IEDs were observed in 62% (resp. 38%) of patients with neocortical epilepsies. This HbR/HbO response was most significant in the epileptic focus region among all the activations in 28%/21% of patients.
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http://dx.doi.org/10.1016/j.eplepsyres.2013.12.011DOI Listing
March 2014

Neurophysiological correlates of auditory and language development: a mismatch negativity study.

Dev Neuropsychol 2013 ;38(6):386-401

Research Center, University Hospital Center Sainte-Justine, Montreal, Canada.

During child development, physiological changes occur in the auditory cortex, which are reflected by differences in the electrophysiological signals. This study aimed to examine the age-related changes of the Mismatch Negativity component (MMN) in response to speech and non-speech stimuli in a cross-sectional design. Results revealed distinct patterns of activation according to stimulus type and age. Age-related differences for tone discrimination occurred earlier in children's development than did the discriminative process for speech sounds. Therefore, networks involved in speech processing are still immature in late childhood and may be more vulnerable to physiological changes.
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http://dx.doi.org/10.1080/87565641.2013.805218DOI Listing
March 2014

Wireless recording systems: from noninvasive EEG-NIRS to invasive EEG devices.

IEEE Trans Biomed Circuits Syst 2013 Apr;7(2):186-95

Polystim Neurotechnologies Laboratory, Electrical Engineering Department, Polytechnique Montréal, QC H3T1J4, Canada.

In this paper, we present the design and implementation of a wireless wearable electronic system dedicated to remote data recording for brain monitoring. The reported wireless recording system is used for a) simultaneous near-infrared spectrometry (NIRS) and scalp electro-encephalography (EEG) for noninvasive monitoring and b) intracerebral EEG (icEEG) for invasive monitoring. Bluetooth and dual radio links were introduced for these recordings. The Bluetooth-based device was embedded in a noninvasive multichannel EEG-NIRS system for easy portability and long-term monitoring. On the other hand, the 32-channel implantable recording device offers 24-bit resolution, tunable features, and a sampling frequency up to 2 kHz per channel. The analog front-end preamplifier presents low input-referred noise of 5 μ VRMS and a signal-to-noise ratio of 112 dB. The communication link is implemented using a dual-band radio frequency transceiver offering a half-duplex 800 kb/s data rate, 16.5 mW power consumption and less than 10(-10) post-correction Bit-Error Rate (BER). The designed system can be accessed and controlled by a computer with a user-friendly graphical interface. The proposed wireless implantable recording device was tested in vitro using real icEEG signals from two patients with refractory epilepsy. The wirelessly recorded signals were compared to the original signals recorded using wired-connection, and measured normalized root-mean square deviation was under 2%.
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http://dx.doi.org/10.1109/TBCAS.2013.2255595DOI Listing
April 2013

Induced gamma-band response to fragmented images: An intracranial EEG study.

Neuropsychologia 2013 Mar 12;51(4):584-91. Epub 2013 Jan 12.

Centre de Recherche en Neuropsychologie et Cognition, Université de Montréal, Montréal, QC, Canada H3C 3J7.

Induced gamma-band response (iGBR) has been linked to coherent perception of images and is thought to represent the synchronisation of neuronal populations mediating binding of elements composing the image and the comparisons with memory for proper recognition. This study uses fragmented images with intracranial electroencephalography to investigate the precise spatio-temporal dynamic of iGBR elicited by the recognition of objects presented for the first time and 24h later. Results show an increased iGBR at recognition in regions involved in bottom-up processes such as the cuneus and the lateral occipital complex. Top-down facilitation involved the lingual gyrus, the precuneus and the superior parietal lobule when images were presented for the first time. Twenty-four hours later, top-down facilitation was mediated by frontal areas involved in retrieval from episodic memory. This study showed that the classically reported iGBR is related to object recognition and that top-down processes vary according to task demand.
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http://dx.doi.org/10.1016/j.neuropsychologia.2013.01.002DOI Listing
March 2013

Functional near-infrared spectroscopy for the assessment of overt reading.

Brain Behav 2012 Nov 28;2(6):825-37. Epub 2012 Oct 28.

École d'orthophonie et d'audiologie, Université de Montréal Montréal, Canada ; Centre de recherche en neuropsychologie et cognition, Université de Montréal Montréal, Canada ; Centre de recherche de l'Hôpital Sainte-Justine, Hôpital Sainte-Justine Montréal, Canada.

Functional near-infrared spectroscopy (fNIRS) has become increasingly established as a promising technique for monitoring functional brain activity. To our knowledge, no study has yet used fNIRS to investigate overt reading of irregular words and nonwords with a full coverage of the cerebral regions involved in reading processes. The aim of our study was to design and validate a protocol using fNIRS for the assessment of overt reading. Twelve healthy French-speaking adults underwent one session of fNIRS recording while performing an overt reading of 13 blocks of irregular words and nonwords. Reading blocks were separated by baseline periods during which participants were instructed to fixate a cross. Sources (n = 55) and detectors (n = 16) were placed bilaterally over frontal, temporal, parietal, and occipital regions. Two wavelengths were used: 690 nm, more sensitive to deoxyhemoglobin (HbR) concentration changes, and 830 nm, more sensitive to oxyhemoglobin (HbO) concentration changes. For all participants, total hemoglobin (HbT) concentrations (HbO + HbR) were significantly higher than baseline for both irregular word and nonword reading in the inferior frontal gyri, the middle and superior temporal gyri, and the occipital cortices bilaterally. In the temporal gyri, although the difference was not significant, [HbT] values were higher in the left hemisphere. In the bilateral inferior frontal gyri, higher [HbT] values were found in nonword than in irregular word reading. This activation could be related to the grapheme-to-phoneme conversion characterizing the phonological pathway of reading. Our findings confirm that fNIRS is an appropriate technique to assess the neural correlates of overt reading.
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http://dx.doi.org/10.1002/brb3.100DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3500469PMC
November 2012

Noninvasive continuous functional near-infrared spectroscopy combined with electroencephalography recording of frontal lobe seizures.

Epilepsia 2013 Feb 13;54(2):331-40. Epub 2012 Nov 13.

Neurology Division, University of Montreal Health Center Notre-Dame Hospital, Montreal, Quebec, Canada.

Purpose: To investigate spatial and metabolic changes associated with frontal lobe seizures.

Methods: Functional near-infrared spectroscopy combined with electroencephalography (EEG-fNIRS) recordings of patients with confirmed nonlesional refractory frontal lobe epilepsy (FLE).

Key Findings: Eighteen seizures from nine patients (seven male, mean age 27 years, range 13-46 years) with drug-refractory FLE were captured during EEG-fNIRS recordings. All seizures were coupled with significant hemodynamic variations that were greater with electroclinical than with electrical seizures. fNIRS helped in the identification of seizures in three patients with more subtle ictal EEG abnormalities. Hemodynamic changes consisted of local increases in oxygenated (HbO) and total hemoglobin (HbT) but heterogeneous deoxygenated hemoglobin (HbR) behavior. Furthermore, rapid hemodynamic alterations were observed in the homologous contralateral region, even in the absence of obvious propagated epileptic activity. The extent of HbO activation adequately lateralized the epileptogenic side in the majority of patients.

Significance: EEG-fNIRS reveals complex spatial and metabolic changes during focal frontal lobe seizures. Further characterization of these changes could improve seizure detection, localization, and understanding of the impact of focal seizures.
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http://dx.doi.org/10.1111/epi.12011DOI Listing
February 2013

Nonlinear hemodynamic responses in human epilepsy: a multimodal analysis with fNIRS-EEG and fMRI-EEG.

J Neurosci Methods 2012 Mar 25;204(2):326-40. Epub 2011 Nov 25.

Département de génie électrique and Institut de génie biomédical, École Polytechnique de Montréal, C.P. 6079, Succ. Centre-ville, Montréal, Qc, Canada H3C 3A7.

Functional magnetic resonance imaging (fMRI) combined with electroencephalography (fMRI-EEG) is a neuroimaging technique based on the blood oxygenation level dependent (BOLD) signal which has been shown to be useful in the study of epilepsy for the localization of the epileptogenic focus. Functional near-infrared spectroscopy (fNIRS) combined with EEG (fNIRS-EEG) is another imaging technique based on the measurement of oxygenated and deoxygenated hemoglobin with complementary clinical potential in epilepsy, for continuous patient monitoring, language lateralization, and focus localization. In this work fMRI-EEG and fNIRS-EEG are used to quantify nonlinear hemodynamic responses in three cases of human refractory focal epilepsy, by using the Volterra kernel expansion up to second order. Prior to analyzing real data, extensive simulations are carried out to show that nonlinearities are estimable. The Volterra methodology is then applied to multimodal data recorded from 3 epileptic patients selected for their frequent spiking activity. Care is taken to account for variability of hemodynamic responses due to other causes than Volterra nonlinearities. Statistically significant nonlinearities are observed for all patients and all modalities. Good concordance between fNIRS and fMRI is found for both the amplitude of the Volterra responses, and, with limitations, in the localization of the epileptic focus and regions of inverted responses (negative BOLD signals). In one patient, Volterra nonlinearities allowed epileptic focus identification with fMRI, while analyses without nonlinearities failed to see it. In simulations when nonlinearities were included, analysis without Volterra nonlinearities performed poorly. These two observations suggest routinely checking for nonlinearities in functional imaging of patients presenting with frequent spikes.
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http://dx.doi.org/10.1016/j.jneumeth.2011.11.016DOI Listing
March 2012

Specific functional asymmetries of the human visual cortex revealed by functional near-infrared spectroscopy.

Brain Res 2012 Jan 9;1431:62-8. Epub 2011 Nov 9.

Centre de Recherche, Centre Hospitalier Universitaire Sainte-Justine, 3175 Chemin de la Côte Sainte-Catherine, Montréal, Canada H3T 1C5.

Based on multiple invasive reports and neuroimaging studies, it is well established that the cytoarchitecture of the visual cortex is related to its functional organization, namely, its retinotopy. The present study aimed to further investigate retinotopic mapping as well as specific vertical and horizontal functional asymmetries within the human visual cortex using functional near-infrared spectroscopy (fNIRS). Black and white wedge checkerboard stimuli were randomly presented to the four visual field (VF) quadrants of eight healthy adults in order to quantify and compare the localization and the amplitude of hemodynamic cortical responses to each VF quadrant. Results showed the expected activation in the contralateral hemisphere, with respect to the side of the stimulated quadrant. We also measured significantly stronger activations in the upper visual cortex when low hemifield stimuli were presented compared to activations in the lower visual cortex when upper hemifield stimuli were shown, especially when the stimulation was presented in the right visual field. These findings confirm the vertical asymmetry of the visual cortex previously reported by neuroimaging and behavioral studies. More importantly, the present work confirms the reliability of the fNIRS technique for functional mapping of the human brain.
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http://dx.doi.org/10.1016/j.brainres.2011.11.008DOI Listing
January 2012
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