Neuropsychological Profile of Childhood Apraxia of Speech: Implicit Learning and Executive Functions

The purpose of this thesis is to analyze the neuropsychological profile of children with idiopathic Childhood Apraxia of Speech (CAS), in particular in relation to transversal processes such as implicit learning and Executive Functions (EFs). Treatment implications are also investigated through a systematic review and metanalysis. In the first study, implicit learning processes were investigated in twenty-five children with CAS, aged between 4 and 12 years and matched for IQ and age to a control group of 25 typically developing children. Implicit learning of participants was assessed by the Serial Reaction Time Task. Children with CAS did not show implicit learning, as documented by the absence of differences between Reaction Times in the sequenced block and the random block, usually considered as a measure of implicit learning effect. The second study aimed at defining the EF profile in a group of 30 preschool children with idiopathic CAS, investigating the relationship between EFs, speech severity and connectivity of the Frontal Aslant Tract (FAT), a white matter tract involved in the neural circuits of both speech and EFs. The results showed the presence of multiple alterations in the EF profile, mainly in its basic components, such as inhibition and working memory. A significant reduction in Fractional Anisotropy (FA) in left pre- Supplementary Motor Area (preSMA) and Supplementary Motor Area (SMA) components of FAT, compared to TD children, was found. Only speech severity correlated and predicted FA value along FAT in both of its components investigated (SMA and pre-SMA) and EF impairment moderated this relation. In particular, a significant role of visuo-spatial working memory in moderating the relationship between speech severity and FA value along FAT in the left SMA component was found. Our findings support the conceptualization of CAS not only as a motor-speech disorder, but also involving transversal processes such as implicit learning and Executive Functions, in a composite and complex picture. The results obtained underline the importance of a comprehensive multidisciplinary assessment, which becomes mandatory in order to provide a more in-depth characterization of the disorder and define the most appropriate therapy interventions. Finally, as a consequence of the results obtained from the previous study, a systematic review and meta-analysis of the literature about the potential of EF treatments to produce enhancements of skills not directly trained, defined as far effects, has been conducted. Despite less considered, these trainings could be extremely relevant to reduce the negative impact of a disorder’s core symptomatology. The study aimed to investigate the far effect outcomes after EF training in children with different types of neurodevelopmental disorders. 17 studies met the inclusion criteria for the systematic review, while 15 studies were selected in the metanalysis. An overall statistically significant effect size was found in the majority of far effect outcome measures considered in the studies. In particular, trainings on executive functions determine significant far effects on daily life functioning and clinical symptoms. Despite a high variability of the results, intensity, frequency, and the laboratory/life contexts dimension seem to be the most influential variables in determining far effects. This systematic review and metanalysis highlights the need to measure the far effects of executive function training in neurodevelopmental disorders, selecting treatments not only on directly targeted processes, but also according to far impacts on the functional weakness of the disorder.