La relation entre le stress vécu par les bébés et la suppression neuronale mesurée en EEG

L’apprentissage et la mémoire sont sensibles aux effets du stress, et il a été démontré que chez l’adulte la relation entre le stress et l’apprentissage suit une courbe en « U » inversé. Cependant, il y a peu de données dans la littérature démontrant l’existence d’une telle relation chez les nourrissons. Dans ce mémoire, nous utilisons le phénomène de suppression neuronale et le cortisol salivaire recueilli en situation de stress afin de mesurer la relation entre le stress et l’apprentissage chez le nourrisson. Nous posons l’hypothèse que le stress affectera la suppression neuronale en suivant aussi une relation en « U » inversé. Nous avons mesuré en électroencéphalographie la réponse cérébrale pendant une tâche d’apprentissage et recueillis des échantillons de salive durant l’expérimentation chez 35 bébés (18 mâles) âgés entre 6 et 26 mois. Nous avons utilisé un modèle linéaire mixte afin de mesurer l’effet du stress sur l’apprentissage en incluant le niveau de cortisol salivaire, l’âge et le sexe comme prédicteurs. Les résultats démontrent que chez les jeunes enfants, un niveau de stress plus élevé n’est pas associé à une diminution de la réponse de suppression neuronale mais est plutôt lié à une réponse cérébrale plus élevée au premier stimulus de chaque essai. Compte tenu de ces résultats, le stress peut être considéré comme de la vigilance, expliquant ainsi cet effet du stress sur la réponse d’apprentissage chez le nourrisson. Puisque nous en savons peu sur le stress et l’apprentissage chez les jeunes enfants et que l’enfance est une période critique du développement, les futures recherches devraient continuer d’étudier l’influence du stress sur les mécanismes d’apprentissage et de la mémoire.The over activation of the hypothalamo–pituitary–adrenal (HPA) axis in stress situations can influence learning and memory. Researchers have underlined an inverted-U shape relationship between stress level, and learning and memory, in adults. Whether this model fits learning performances in infants is not well documented. In this study, we use the repetition suppression phenomenon and salivary cortisol collected during a stressful situation to measure the relationship between stress and learning in infants. We hypothesized that the effect of stress on repetition suppression will also follow an inverted-U shape relationship. We measured brain activity using EEG during a repetition-based learning task and saliva samples were collected during the experiment in 35 infants (18 males) aged between 6 and 26 months. The effect of stress level on learning was modeled with a linear mixed model, using cortisol, age and sex as predictors. Results indicate that in healthy infants, higher stress level is not associated with poorer repetition suppression response but is rather linked to an increased response on the first stimulus of each trial. Considering these results, stress could be interpreted as vigilance, thus explaining this effect of stress on learning response in infants. Since little is known about stress and learning in infants and considering that early childhood is a critical period of development, future studies should keep investigating the influence of stress on learning and memory mechanisms

Prolonged and unprolonged complex febrile seizures differently affect frontal theta brain activity

Objective: Studies have identified persistent cognitive and functional deficits, which could be linked to each other, in children with complex febrile seizures (FS). Our aim was to investigate differences in brain activity in children with a history of complex FS, through a study paradigm associated with the development of learning capacities and using electroencephalographic (EEG) signal. To further increase our understanding of these differences, complex FS were studied separately depending on their type. Method: EEG was recorded in 43 children with past FS. Brain activity associated with auditory learning was investigated using a habituation paradigm, in which repetition suppression (RS) is typically found following stimulus repetition. Auditory stimuli were repeated three times, and each presentation were analysed separately in the time-frequency (TF) domain. A mixedanalysis of variance was used to assess differences in spectral power between stimulus repetition and FS type (simple vs complex prolonged; CP vs complex unprolonged; CUP). Results: Repetition effects were found in the 3-6 Hz during 150-600ms time window after stimulus onset at frontal sites (F(2, 40)=5.645, p=0.007, η2p=0.220). Moreover, an interaction effect between stimulus repetition and FS type (F(4, 80)=2.607, p=0.042, η2p=0.115) was found. Children with CP FS showed greater increase in spectral power in response to the first stimulus presentation, while children with CUP FS failed to show a RS pattern. Significance: Our results show distinct abnormalities in brain activity to a habituation paradigm. We argue that these changes suggest children with CP FS may be hyperexcitable, while children with CUP FS show impaired habituation processes. Still, these differences may be associated with other clinical features linked to complex FS as well. Hence, the role of these differences in complex FS incidence and prognosis should be the subject of future studies

Impact of brain overgrowth on sensorial learning processing during the first year of life

Macrocephaly is present in about 2–5% of the general population. It can be found as an isolated benign trait or as part of a syndromic condition. Brain overgrowth has been associated with neurodevelopmental disorders such as autism during the first year of life, however, evidence remains inconclusive. Furthermore, most of the studies have involved pathological or high-risk populations, but little is known about the effects of brain overgrowth on neurodevelopment in otherwise neurotypical infants. We investigated the impact of brain overgrowth on basic perceptual learning processes (repetition effects and change detection response) during the first year of life. We recorded high density electroencephalograms (EEG) in 116 full-term healthy infants aged between 3 and 11 months, 35 macrocephalic (14 girls) and 81 normocephalic (39 girls) classified according to the WHO head circumference norms. We used an adapted oddball paradigm, time-frequency analyses, and auditory event-related brain potentials (ERPs) to investigate differences between groups. We show that brain overgrowth has a significant impact on repetition effects and change detection response in the 10–20 Hz frequency band, and in N450 latency, suggesting that these correlates of sensorial learning processes are sensitive to brain overgrowth during the first year of life

Effects of eight neuropsychiatric copy number variants on human brain structure

Many copy number variants (CNVs) confer risk for the same range of neurodevelopmental symptoms and psychiatric conditions including autism and schizophrenia. Yet, to date neuroimaging studies have typically been carried out one mutation at a time, showing that CNVs have large effects on brain anatomy. Here, we aimed to characterize and quantify the distinct brain morphometry effects and latent dimensions across 8 neuropsychiatric CNVs. We analyzed T1-weighted MRI data from clinically and non-clinically ascertained CNV carriers (deletion/duplication) at the 1q21.1 (n = 39/28), 16p11.2 (n = 87/78), 22q11.2 (n = 75/30), and 15q11.2 (n = 72/76) loci as well as 1296 non-carriers (controls). Case-control contrasts of all examined genomic loci demonstrated effects on brain anatomy, with deletions and duplications showing mirror effects at the global and regional levels. Although CNVs mainly showed distinct brain patterns, principal component analysis (PCA) loaded subsets of CNVs on two latent brain dimensions, which explained 32 and 29% of the variance of the 8 Cohen’s d maps. The cingulate gyrus, insula, supplementary motor cortex, and cerebellum were identified by PCA and multi-view pattern learning as top regions contributing to latent dimension shared across subsets of CNVs. The large proportion of distinct CNV effects on brain morphology may explain the small neuroimaging effect sizes reported in polygenic psychiatric conditions. Nevertheless, latent gene brain morphology dimensions will help subgroup the rapidly expanding landscape of neuropsychiatric variants and dissect the heterogeneity of idiopathic conditions

EEG repetition and change detection responses in infancy predict adaptive functioning in preschool age: a longitudinal study

Abstract Neurodevelopmental disorders (NDDs) are mostly diagnosed around the age of 4–5 years, which is too late considering that the brain is most susceptive to interventions during the first two years of life. Currently, diagnosis of NDDs is based on observed behaviors and symptoms, but identification of objective biomarkers would allow for earlier screening. In this longitudinal study, we investigated the relationship between repetition and change detection responses measured using an EEG oddball task during the first year of life and at two years of age, and cognitive abilities and adaptive functioning during preschool years (4 years old). Identification of early biomarkers is challenging given that there is a lot of variability in developmental courses among young infants. Therefore, the second aim of this study is to assess whether brain growth is a factor of interindividual variability that influences repetition and change detection responses. To obtain variability in brain growth beyond the normative range, infants with macrocephaly were included in our sample. Thus, 43 normocephalic children and 20 macrocephalic children were tested. Cognitive abilities at preschool age were assessed with the WPPSI-IV and adaptive functioning was measured with the ABAS-II. Time–frequency analyses were conducted on the EEG data. Results indicated that repetition and change detection responses in the first year of life predict adaptive functioning at 4 years of age, independently of head circumference. Moreover, our findings suggested that brain growth explains variability in neural responses mostly in the first years of life, so that macrocephalic children did not display repetition suppression responses, while normocephalic children did. This longitudinal study demonstrates that the first year of life is an important period for the early screening of children at risk of developing NDDs

Febrile seizures and increased stress sensitivity in children : how it relates to seizure characteristics

BACKGROUND: Studies suggest that the relationship between seizures and stress starts early in life. However, evidence of long-term altered stress reactivity following early-life seizures is lacking. Our objectives were to assess alterations in stress hormone reactivity in children with past febrile seizures (FS) and investigate how these alterations relate to clinical characteristics. METHOD: This case-control study compared a convenience sample of children with simple FS (n = 24), complex FS (n = 18), and matched healthy controls (n = 42). Stress was induced by electrode placement for an electroencephalography (EEG) exam. Salivary cortisol to stress, using three samples collected before and after the stressor, was compared between groups and sex. The relationship between stress reactivity and clinical characteristics (i.e., FS duration, age at first FS, time since the last FS) was investigated. RESULTS: Cortisol reactivity to stress was significantly different depending on study groups, F(1, 78) = 6.415, p = 0.003, η2p = 0.141, but not sex nor was there a significant interaction between group and sex (p ≥ 0.581). Participants with simple FS showed higher cortisol reactivity to stress (M = 14.936, Standard deviation (SD) = 26.852) compared with those with complex FS (M = -4.663, SD = 18.649, p = 0.015) and controls (M = -3.817, SD = 18.907, p = 0.003). There was no significant difference between participants with complex FS and controls (p > 0.999). Stress reactivity was not linked to clinical characteristics. CONCLUSIONS: Children with past simple FS showed greater changes in salivary cortisol following stress, suggesting enhanced stress sensitivity. As similar results were not found in a population with complex FS, our study shows that stress alterations are not caused by seizure severity. Future studies are needed to investigate whether stress sensitivity may be premorbid to simple FS and may contribute to simple FS incidence

Impact of brain overgrowth on sensorial learning processing during the first year of life

Macrocephaly is present in about 2–5% of the general population. It can be found as an isolated benign trait or as part of a syndromic condition. Brain overgrowth has been associated with neurodevelopmental disorders such as autism during the first year of life, however, evidence remains inconclusive. Furthermore, most of the studies have involved pathological or high-risk populations, but little is known about the effects of brain overgrowth on neurodevelopment in otherwise neurotypical infants. We investigated the impact of brain overgrowth on basic perceptual learning processes (repetition effects and change detection response) during the first year of life. We recorded high density electroencephalograms (EEG) in 116 full-term healthy infants aged between 3 and 11 months, 35 macrocephalic (14 girls) and 81 normocephalic (39 girls) classified according to the WHO head circumference norms. We used an adapted oddball paradigm, time-frequency analyses, and auditory event-related brain potentials (ERPs) to investigate differences between groups. We show that brain overgrowth has a significant impact on repetition effects and change detection response in the 10–20 Hz frequency band, and in N450 latency, suggesting that these correlates of sensorial learning processes are sensitive to brain overgrowth during the first year of life

Effects of eight neuropsychiatric copy number variants on human brain structure.

Many copy number variants (CNVs) confer risk for the same range of neurodevelopmental symptoms and psychiatric conditions including autism and schizophrenia. Yet, to date neuroimaging studies have typically been carried out one mutation at a time, showing that CNVs have large effects on brain anatomy. Here, we aimed to characterize and quantify the distinct brain morphometry effects and latent dimensions across 8 neuropsychiatric CNVs. We analyzed T1-weighted MRI data from clinically and non-clinically ascertained CNV carriers (deletion/duplication) at the 1q21.1 (n = 39/28), 16p11.2 (n = 87/78), 22q11.2 (n = 75/30), and 15q11.2 (n = 72/76) loci as well as 1296 non-carriers (controls). Case-control contrasts of all examined genomic loci demonstrated effects on brain anatomy, with deletions and duplications showing mirror effects at the global and regional levels. Although CNVs mainly showed distinct brain patterns, principal component analysis (PCA) loaded subsets of CNVs on two latent brain dimensions, which explained 32 and 29% of the variance of the 8 Cohen's d maps. The cingulate gyrus, insula, supplementary motor cortex, and cerebellum were identified by PCA and multi-view pattern learning as top regions contributing to latent dimension shared across subsets of CNVs. The large proportion of distinct CNV effects on brain morphology may explain the small neuroimaging effect sizes reported in polygenic psychiatric conditions. Nevertheless, latent gene brain morphology dimensions will help subgroup the rapidly expanding landscape of neuropsychiatric variants and dissect the heterogeneity of idiopathic conditions