Motor Adaptation Deficits in Children with Developmental Coordination Disorder and/or Reading Disorder.

Procedural learning has been mainly tested through motor sequence learning tasks in children with neurodevelopmental disorders, especially with isolated Developmental Coordination Disorder (DCD) and Reading Disorder (RD). Studies on motor adaptation are scarcer and more controversial. This study aimed to compare the performance of children with isolated and associated DCD and RD in a graphomotor adaptation task. In total, 23 children with RD, 16 children with DCD, 19 children with DCD-RD, and 21 typically developing (TD) children wrote trigrams both in the conventional (from left to right) and opposite (from right to left) writing directions. The results show that movement speed and accuracy were more impacted by the adaptation condition (opposite writing direction) in children with neurodevelopmental disorders than TD children. Our results also reveal that children with RD have less difficulty adapting their movement than children with DCD. Children with DCD-RD had the most difficulty, and analysis of their performance suggests a cumulative effect of the two neurodevelopmental disorders in motor adaptation.

Activation of the PI3K/AKT/mTOR Pathway in Cajal-Retzius Cells Leads to Their Survival and Increases Susceptibility to Kainate-Induced Seizures.

Cajal-Retzius cells (CRs) are a class of transient neurons in the mammalian cortex that play a critical role in cortical development. Neocortical CRs undergo almost complete elimination in the first two postnatal weeks in rodents and the persistence of CRs during postnatal life has been detected in pathological conditions related to epilepsy. However, it is unclear whether their persistence is a cause or consequence of these diseases. To decipher the molecular mechanisms involved in CR death, we investigated the contribution of the PI3K/AKT/mTOR pathway as it plays a critical role in cell survival. We first showed that this pathway is less active in CRs after birth before massive cell death. We also explored the spatio-temporal activation of both AKT and mTOR pathways and reveal area-specific differences along both the rostro-caudal and medio-lateral axes. Next, using genetic approaches to maintain an active pathway in CRs, we found that the removal of either PTEN or TSC1, two negative regulators of the pathway, lead to differential CR survivals, with a stronger effect in the Pten model. Persistent cells in this latter mutant are still active. They express more Reelin and their persistence is associated with an increase in the duration of kainate-induced seizures in females. Altogether, we show that the decrease in PI3K/AKT/mTOR activity in CRs primes these cells to death by possibly repressing a survival pathway, with the mTORC1 branch contributing less to the phenotype.

Modeling the influence of motor skills on literacy in third grade: Contributions of executive functions and handwriting.

Several nonlanguage factors influence literacy development, and motor skills are among those most studied. Despite the publication of several studies that have supported the existence of this relationship, the type of influence and underlying mechanisms have been little explored. Herein, we propose modeling the relationship between motor skills and literacy through structural equation modeling, testing the contribution of executive functions and handwriting skills as the possible mediators of this relationship. In a study of 278 third-grade children, we used a wide range of measures related to written language (reading, spelling, reading comprehension, and written production), fine motor skills (dominant hand, nondominant hand, and bimanual dexterity), executive functions (verbal and visuospatial working memory, inhibition, and shifting), and handwriting. Structural equation modeling of the relationship between these different variables indicated that in the third grade, the influence of fine motor skills on literacy is fully mediated by both executive functions and handwriting skills. These motor skills effects are observed for both low levels of processing (reading, spelling) and high levels of processing (reading comprehension, written production). The results are discussed in terms of the potential mechanisms underlying different literacy skills and their implications for pedagogical programs.

Procedural learning and retention of audio-verbal temporal sequence is altered in children with developmental coordination disorder but cortical thickness matters.

Rhythmic abilities are impaired in developmental coordination disorder (DCD) but learning deficit of procedural skills implying temporal sequence is still unclear. Current contradictory results suggest that procedural learning deficits in DCD highly depend on learning conditions. The present study proposes to test the role of sensory modality of stimulations (visual or auditory) on synchronization, learning, and retention of temporal verbal sequences in children with and without DCD. We postulated a deficit in learning particularly with auditory stimulations, in association with atypical cortical thickness of three regions of interesting: sensorimotor, frontal and parietal regions. Thirty children with and without DCD (a) performed a synchronization task to a regular temporal sequence and (b) practiced and recalled a novel non-regular temporal sequences with auditory and visual modalities. They also had a magnetic resonance imaging to measure their cortical thickness. Results suggested that children with DCD presented a general deficit in synchronization of a regular temporal verbal sequence irrespective of the sensory modality, but a specific deficit in learning and retention of auditory non-regular verbal temporal sequence. Stability of audio-verbal synchronization during practice correlated with cortical thickness of the sensorimotor cortex. For the first time, our results suggest that synchronization deficits in DCD are not limited to manual tasks. This deficit persists despite repeated exposition and practice of an auditory temporal sequence, which suggests a possible alteration in audio-verbal coupling in DCD. On the contrary, control of temporal parameters with visual stimuli seems to be less affected, which opens perspectives for clinical practice.

Rhythm in the blood: The influence of rhythm skills on literacy development in third graders.

Several studies have shown the influence of rhythm skills on the processing of written language, especially at the beginning of literacy development. The first objective of this study was to determine the persistence of this link at an advanced grade level. The second objective was to better understand the factors underlying this relationship and, more specifically, to examine the hypothesis of mediation by phonological and/or motor skills. In total, 278 third graders performed literacy tasks (word/pseudoword decoding and spelling), a rhythm production task, two phonological tasks (phonological awareness and rapid automatized naming), and motor tasks. Significant correlations were observed between literacy and each of rhythm skills, phonological skills, and motor skills. However, structural equation models showed that the influence of rhythm skills on literacy was mediated neither by phonological skills nor by motor abilities. These results suggest that rhythm skills continue to play a role in the acquisition of written language in third graders and that this contribution seems to be independent of phonological and motor skills.