Neural bases of handwriting in adults and children : from spelling to gesture

L’écriture est une habileté qui nous parait si simple et commune qu’on oublie parfois les années d'entraînements nécessaires à sa maîtrise. L’écriture est fascinante car elle allie une expertise linguistique et une expertise motrice. L’étude des bases neurales de l’écriture est un champ de recherche émergeant, et la nature des relations entre ses différentes composantes est encore largement débattue. En outre, on ne connait rien des bases cérébrales de son apprentissage. Ce travail de thèse nous a permis de montrer, chez l’adulte, qu’orthographe et geste ne sont pas indépendants. Nos données indiquent que les processus orthographiques sont toujours actifs quand l’écriture est exécutée, et que les régions cérébrales codant le geste d’écriture sont sensibles à la difficulté orthographique des mots produits. Cette observation nous a permis de contribuer au débat concernant l’indépendance des différents processus. De plus, nous avons pu caractériser le réseau cérébral sous-tendant l’écriture chez des enfants de 8-11 ans. Nous avons montré que le réseau principal est déjà établi et fonctionnel chez les enfants. Les différences entre enfants et adultes résident principalement dans l’activation de régions cérébrales impliquées dans des processus attentionnels et de contrôle (cortex préfrontal, cervelet). La suite immédiate de cette étude sera de tester quelle est la sensibilité de ce réseau à la difficulté orthographique des mots chez l’enfant en cours d’apprentissage. Plus généralement ce travail ouvre des perspectives pour une meilleure compréhension de la dysgraphie développementale et de l’apprentissage moteur.Writing is a skill that seems so simple and common that we sometimes forget the years of training necessary to master it. Writing is fascinating because it combines linguistic and motor expertise. While the study of the neural bases of writing is an emerging field of research, the nature of the relationships between its different components is still being debated. Likewise, very little is known about the neural bases of learning how to write. This PhD work has allowed to highlight, in adults, the existence of an interaction between spelling and motor processes during writing. In addition, we were able to characterize the neural network of handwriting in children aged 8-11 years. Interestingly, the main network is already established and functional in children. The differences with adults lie in the activation of brain regions involved in attention and control processes (prefrontal cortex préfrontal, cerebellum). The immediate perspective of this study will be the assessment of the sensitivity of this network to orthographic difficulty in children. More generally, my work opens the way for a better understanding of developmental dysgraphia and motor learning

Motor control of handwriting in the developing brain: A review

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The handwriting brain in middle-childhood

International audienceRunning title: The handwriting brain of children Research Highlights • We used fMRI to uncover the brain correlates of writing acquisition and demonstrate that the network previously described in adults is also strongly activated in children. • However, group effects in the right cerebellum and left fusiform gyrus indicate that the network continues to mature between middle childhood and adulthood. • We also found group differences in prefrontal and precentral regions, which likely underpin changes in the control of writing with the acquisition of expertise. • These results fill a considerable gap in the field of writing acquisition. Abstract While the brain network supporting handwriting has previously been defined in adults, its organization in children has never been investigated. We compared the handwriting network of 23 adults and 42 children (8 to 11 year old). Participants were instructed to write the alphabet, the days of the week and to draw loops while being scanned. The handwriting network previously described in adults (5 key regions: left dorsal premotor cortex, superior parietal lobule, fusiform and inferior frontal gyri, and right cerebellum) was also strongly activated in children. The right precentral gyrus and the right anterior cerebellum were more strongly activated in adults than in children while the left fusiform gyrus was more strongly activated in children than in adults. Finally, we found that, contrary to adults, children recruited prefrontal regions to complete the writing task. This constitutes the first comparative investigation of the neural correlates of writing in children and adults. Our results suggest that the network supporting handwriting is already established in middle-childhood. They also highlight the major role of prefrontal regions in learning this complex skill and the importance of right precentral regions and cerebellum in the performance of automated handwriting

Corrélats cérébraux de l’écriture manuscrite chez l’adulte et l’enfant

International audienceDans cet article, nous présentons l’organisation des aires cérébrales impliquées dans l’écriture manuscrite chez l’adulte, et nous décrivons des données récentes sur cette organisation dans le cerveau d’enfants en cours d’apprentissage. Chez l’adulte, le réseau impliqué comprend un ensemble de régions pariéto-frontales gauches, le gyrus fusiforme gauche et le cervelet droit. Ces régions codent les aspects orthographiques et moteurs de l’écriture manuscrite. Chez l’enfant de huit à 11 ans, les régions bien décrites chez l’adulte sont également actives : le réseau del’écriture est déjà structuré. Cependant, des différences observées entre les deux groupes dans le niveau d’activation de certains éléments du réseau, dans le recrutement d’autres régions ou dans la latéralisation des activations témoignent d’un processus en cours d’automatisation

The impact of spelling regularity on handwriting production: A coupled fMRI and kinematics study

International audienceCurrent models of writing assume that the orthographic processes involved in spelling retrieval and the motor processes involved in the control of the hand are independent. This view has been challenged by behavioral studies, which showed that the linguistic features of words impact motor execution during handwriting. We designed an experiment coupling functional magnetic resonance imaging and kinematic recordings during a writing to dictation task. Participants wrote orthographically regular and irregular words. The presence of an irregularity impacts both the initiation of the movement and its fine motor execution. At the brain level, the left inferior frontal and fusiform gyri, two regions belonging to the core of the written language system, were found to be sensitive to the presence of an irregularity and to its position in the word during writing execution. Moreover, the left superior parietal lobule, the left superior frontal gyrus and the right cerebellum, three motor-related regions, displayed a stronger response to irregular than regular words. These results constitute direct evidence that orthographic and motor processes occur in a continuous and interactive fashion during writing

Estimation of the cortical microconnectome from in vivo spiking activity in the macaque monkey

The typical range of local connectivity in the cerebral cortex delineates columnar microcircuits, within which the layer- and population-specific connectivities present features that are preserved across species and cortical areas. However, when considered in more detail, the internal connectivity structure, i.e. the microconnectome (MC), of such microcircuits is variable across cortical areas. Furthermore, the parameters describing the MC are largely unknown for most cortical areas.Models constructed based on structural data have been able to recover realistic first-order spike train statistics in early sensory cortical areas [1, 2]. These bottom-up models can be constructed owing to the availability of extensive anatomical and physiological data from early visual and somatosensory areas. However, such measurements are less abundant for higher-order cortices, limiting bottom-up modeling until further biological measurements are published.Here we present an analysis that aims to overcome some of the limitations in currently available anatomical data. We use experimentally measured electrophysiological activity from vision-related and motor areas to constrain the connectivity of cortical microcircuit models and infer area-specific features of the MC. The novel experimental data consist of simultaneous layer-resolved laminar recordings from macaque primary motor (M1) and premotor (PMd) cortices [3]; as well as acute simultaneous recordings of macaque dorsolateral prefrontal cortex (dlPFC) and visual area V4. All data were recorded during resting-state sessions, i.e. while the subjects were not performing any task. Data from the resting state are expected to deliver rich dynamics related to the underlying connectivity structure [4].We explore the parameter space of the MC with an evolutionary algorithm using biologically inspired spiking cortical microcircuit models. During the parameter estimation phase, a set of standardized statistical tests, based on established single-neuron and population statistics [5], are used to score the similarity between the simulated data and experimental recordings. The score is calculated based on the overlap between experimental and simulated data statistics via the Wasserstein distance. Parameter estimates are obtained by maximizing this score, and are then validated against a separate set of statistics, which were not used in the estimation phase. Finally, we assess the similarities and differences of estimated model parameters across areas.Future work will integrate these local visual and motor models into a large-scale visuomotor cortical multi-area model, extending the work in [2, 6].References:1. Potjans TC, Diesmann M. Cereb Cortex 2014, 24(3), 785–8062. Schmidt M, Bakker R et al. Brain Struct Func 2017, 223, 1409–14353. Kilavik BE. SfN 2018. Online4. Dąbrowska P, Voges N et al. On the complexity of resting state spiking activity in monkey motor cortex. In preparation5. Gutzen R, von Papen M et al. Front Neuroinform 2018, 12:906. Schmidt M, Bakker R et al. PLOS CB 2018, 14, e100635