Trait dissociation has not been examined from a structural human brain mapping perspective in healthy adults or children. Non-pathological dissociation shares some features with daydreaming and mind-wandering, but also involves subtle disruptions in affect and autobiographical memory.

To identify neurostructural biomarkers of trait dissociation in healthy children.

Typically developing 9- to 15-year-olds (n = 180) without psychological or behavioural disorders were enrolled in the Developmental Chronnecto-Genomics (DevCoG) study of healthy brain development and completed psychological assessments of trauma exposure and dissociation, along with a structural T1-weighted magnetic resonance imaging. We conducted univariate ANCOVA generalised linear models for each region of the default mode network examining the effects of trait dissociation, including scanner site, age, gender and trauma as covariates and correcting for multiple comparison.

We found that the precuneus was significantly larger in children with higher levels of trait dissociation but this was not related to trauma exposure. The inferior parietal volume was smaller in children with higher levels of trauma but was not related to dissociation. No other regions of interest, including frontal and limbic structures, were significantly related to trait dissociation even before multiple comparison correction.

Trait dissociation reflects subtle cognitive disruptions worthy of study in healthy people and warrants study as a potential risk factor for psychopathology. This neurostructural study of trait dissociation in healthy children identified the precuneus as an essential brain region to consider in future dissociation research.

Le mind-wandering est ce phénomène connu de tous, où l’attention décroche et « vagabonde » au gré de pensées sans lien avec la tâche en cours [1]. Dans une tâche de go/no-go, les épisodes de déconcentration entrainent une diminution des performances et une augmentation de la variabilité des temps de réponse, par rapport aux périodes où l’attention est soutenue [2]. Mais le déficit d’attention n’est pas spécifique du TDA/H (Trouble Déficit d’Attention avec ou sans Hyperactivité) car il est présent dans d’autres pathologies comme par exemple la dépression [3]. Dans cette étude nous recherchons une différence de profils attentionnels liés au « mind wandering », qui serait spécifique au TDA/H.

Au moyen d’un go/no-go interrompu par des rapports subjectifs du contenu de la pensée, nous avons mené la même expérience, à la fois dans des populations d’enfants et d’adultes, en comparant des groupes de sujets TDA/H, des groupes de sujets contrôles cliniques et sains.

Nous mettons en évidence une augmentation significative de pensées floues ou vides (mind-blanking[4]), chez les sujets TDA/H enfants et adultes.

Cette augmentation de pensées impossibles à rapporter, semble spécifique du TDA/H. Pour maintenir l’attention focalisée comme pour prolonger un épisode de rêverie éveillée, de bonnes fonctions exécutives semblent nécessaires [1]. Or le TDA/H se caractérise par un déficit de fonctions exécutives [5], ce qui impliquerait donc une alternance plus rapide entre cours externe et interne de pensées soit une durée moyenne des épisodes de focus attentionnel ou de rêverie, plus brève. Un stimulus qui ne dure pas suffisamment longtemps ne peut faire l’objet d’un rapport verbal car non accessible à la conscience [6]. Le mind-blanking pourrait être un marqueur indirect d’un fil de pensées trop labile pour être accessible à la conscience.

Attention-deficit/hyperactivity disorder (ADHD) is a developmental condition that profoundly affects quality of life. Although mounting evidence now suggests uncontrolled mind-wandering as a core aspect of the attentional problems associated with ADHD, the neural mechanisms underpinning this deficit remains unclear. To that extent, competing views argue for (i) excessive generation of task-unrelated mental content, or (ii) deficiency in the control of task-relevant cognition.

In a cross-sectional investigation of a large neurotypical cohort (n = 184), we examined alterations in the intrinsic brain functional connectivity architecture of the default mode (DMN) and frontoparietal (FPN) networks during resting state functional magnetic resonance imaging in relation to ADHD symptomatology, which could potentially underlie changes in ongoing thought within variable environmental contexts.

The results illustrated that ADHD symptoms were linked to lower levels of detail in ongoing thought while the participants made more difficult, memory based decisions. Moreover, greater ADHD scores were associated with lower levels of connectivity between the DMN and right sensorimotor cortex, and between the FPN and right ventral visual cortex. Finally, a combination of high levels of ADHD symptomology with reduced FPN connectivity to the visual cortex was associated with reduced levels of detail in thought.

The results of our study suggest that the frequent mind-wandering observed in ADHD may be an indirect consequence of the deficient control of ongoing cognition in response to increasing environmental demands, and that this may partly arise from dysfunctions in the intrinsic organisation of the FPN at rest.