A study of EEG coherence in DCD children during motor synchronization task.

This paper investigates the hypothesis that the coordination difficulties of DCD children are associated with an increased coherence in the cortical motor regions, which persists with age. Forty-eight children participated in the study (24 DCD and 24 Controls). Their ages ranged from 8 to 13 years, divided into three groups (8-9, 10-11, and 12-13 years old). Children were required to perform finger flexion or extension either in synchrony or in syncopation with a rhythmic metronome, while a 32-channel EEG was recorded. Along with stability measures of motor performance, we analyzed the spectral EEG coherence between intrahemispheric (left frontal/left central; left central/left parietal) and interhemispheric (left central/right central) sites. Spectral coherence assesses functional coupling between distant areas of the brain. Two frequency bands related to sensorimotor activation were chosen: alpha (8-12 Hz) and beta (12-30 Hz). The synchrony task was chosen as a rest condition against which the two syncopation conditions at 0.5 Hz and 1.3 Hz were contrasted. For intrahemispheric comparison, 8-9-year-old DCD children showed that coherence between fronto-central regions increased for both rhythms and conditions, as compared to controls. No difference was found for interhemispheric comparisons. As frontal sites are related to motor planning, our results suggest that youngest DCD children were forced to maintain a high level of pre-programming to compensate for the difficulties caused by the perceptual-motor requirements of the task in light of their coordination disorder.

Motor impairment in dyslexia: the influence of attention disorders.

Developmental dyslexia is a heterogeneous syndrome with a phonological core deficit and frequent association with other developmental disorders. Controversies exist about the influence of motor difficulties frequently encountered in dyslexia. According to different theoretical approaches, these motor impairments would reflect either a frequent co-morbid entity or a cerebellar dysfunction that could constitute the causal factor of reading disabilities. The principal aim of this study was to determine the frequency of motor impairments in a population of children with phonological dyslexia and specify possible links with attention deficit. We analysed retrospectively motor and attention abilities of 58 children with phonological dyslexia. An important sub-group of children with dyslexia (40-57% depending on the severity of motor difficulties) presented a motor impairment affecting co-ordination, balance and manual dexterity suggesting a cerebellar dysfunction. There was a significant association between attention deficit and motor impairments, with a specific impact on balance and co-ordination deficits. The comparison of performance in four groups defined according to the presence versus absence of attention deficit and motor impairment, respectively, were not in favour of a unequivocal causal link between reading disabilities and motor or attention disorders.

Developmental coordination disorder pertains to a deficit in perceptuo-motor synchronization independent of attentional capacities.

We investigated from a dynamic pattern perspective to motor coordination whether the deficiency in motor coordination characterizing Developmental Coordination Disorder children pertains to a general disorder in synchronization leading to a lower stability of the performed coordination pattern, and the extent to which the trouble is linked to attentional capacities. Twenty-four DCD children without ADHD aged eight to thirteen and 60 control children were asked (1) to perform a Continuous Performance Test assessing sustained attention; (2) to flex one finger either in synchrony or in syncopation with a visual periodic signal whose frequency was increased stepwise, assessing synchronization abilities. For the attentional task, percentage of exact responses, number of errors and reaction time were recorded. For the synchronization task, we measured relative phase (i.e., the ratio between the stimulus and the response onset and the time separating two successive stimuli). DCD children were significantly more variable than controls in both conditions and the difficulty in synchronization was unrelated to attentional disorders (ANCOVA). These findings support the idea of a general synchronization disorder in DCD children underlying their poor motor coordination. Moreover, this synchronization disorder does not appear to be strictly dependent on the level of sustained attentional capacities.