Executive functioning (EF) is a set of interrelated high-level cognitive skills related to daily life skills, academic success and social functioning that develops over childhood. However, there is still limited knowledge about factors that may influence its development. Investigations of atypical developmental trajectories may broaden the understanding of the relationship between nature and nurture in EF development, and provide important tests of claims of universality of developmental processes.
Cerebral palsy (CP), the most common cause of severe motor impairment in children, implies an increased risk of cognitive impairment. There is large variability in functioning, and this variability makes the group suitable for exploring factors contributing to variability in EF. Children with CP who are motor impaired and unable to speak, can use communication aids with graphic symbols or letters. This form of aided communication is complex and it has been suggested that it places extra demands on executive functions compared to speech.
All the studies have a cross-sectional design and included two main samples; a geographical cohort of 73 children aged 5;1 to 17;7 years with a diagnosis of CP and a sample of 29 participants using communication aids and 27 using natural speech, aged 6;7 to 15;11 years. Cognitive functioning was investigated with neuropsychological tests, structured tasks where the participants should instruct another person to construct models that the participant but not the partner could see, and parental evaluations. Adapted versions of the tests were used, where the motor impaired participants could respond with finger or eye gaze pointing.
Even though the risk of cognitive impairment is well known, the variability is not yet well described as children with the most severe speech and motor impairments are often not assessed. The first study describes the neuropsychological profiles of a geographical cohort of children with CP. It was found that IQ scores ranged from 19 to 123 with a mean around 80. Twenty-four percent had severe enough social and adaptive problems to be diagnosed with an intellectual disability. This is in the lower range of what has previously been reported, and may reflect that cognition was assessed with methods that enabled all the children to show their abilities regardless of degree of speech and motor impairment. Twenty-one percent of the children with CP had an uneven cognitive profile, and a majority had higher scores on verbal comprehension than on perceptual reasoning. The presence of epilepsy and a MRI pattern consistent with brain maldevelopment were negatively associated with cognitive functioning. There was an association, but no 1:1 relationship, between motor and cognitive functioning.
The second and third studies explore the relationships between EF, motor functioning and language comprehension and use. In children with CP, the considerable variation in EF was related to verbal comprehension and perceptual reasoning, but not to level of speech and motor impairments. The results on tests of EF were comparatively better than IQ in the oldest group of children with CP. Aided communication taxes EF more than speech, but children using spelling showed planning ability comparable to typically developing peers.
The fourth study evaluates the factor structure of EF, relating it to Anderson’s (2002) conceptual model of the development of EF. The results showed a unitary structure, and thus that Anderson’s model is not well suited to describe EF in children with speech and motor impairments.
In summary, the results indicate that development of EF is not dependent upon development of motor skills or speech, nor on mode of communication, but that it is closely related to overall cognitive development. Moreover, the development of EF seemed to be delayed in the children with CP but also to catch up, but longitudinal studies are needed to explore this further.