The past few decades have seen an explosion of interest in early childhood brain damage, leading to advances in acute medical treatments and providing important insights into the unique impact of early brain injury on the developing brain. Researchers and clinicians working with these children have become aware that injuries to the developing brain cannot necessarily be understood or treated in the same manner as those occurring in adulthood. While one might be guided by adult models, there are unique developmental and contextual issues that need to be taken into account at all stages of recovery and treatment in children. A number of principles have been established, some consistent with the adult literature, for example, the mechanics and characteristic pathology of injury and the predictive value of severity of insult. Others are specific to early brain injury, reflecting the importance of developmental considerations, such as age at injury, developmental stage of brain development and functional maturation, the key role of the family and implications of life tasks specific to children. It has been necessary to build a somewhat separate knowledge base for early brain insult and, as a consequence, until recently, our understanding of recovery and outcomes has lagged behind that for adults.
Of crucial importance is growing evidence for a developmentally-specific response to early insult. The relative vulnerability of the young brain to disruption or damage and the behavioural consequences in terms of reduced skill and knowledge acquisition is an evolving concept and is now supported by animal research, neuro-imaging data and behavioural findings. Longitudinal studies suggest that damage to the young brain may be more detrimental than similar insults in adulthood and that young children may ‘grow into’ their impairments with time since insult, broadening the gap between their skills and those of age peers. These findings are yet to be incorporated into clinical practice or reflected in availability of appropriate medical, educational and rehabilitative resources.
Findings from a range of mostly discipline-specific research endeavours describe an increased risk for a multitude of residual impairments following childhood brain insult, both acutely and in the long-term: persisting neurological symptoms, motor dysfunction, communication difficulties, poor attention and information processing, reduced memory, executive dysfunction and social and emotional disorders have been consistently reported. In association with these impairments, functional domains are also likely to be impacted, with solid evidence of low school attainment, reduced vocational opportunities, poor adaptive skills and lowered quality of life. Unfortunately, while these problems are now accepted as frequent consequences of childhood brain insult, findings are only beginning to be translated into more precise prognoses or acceptable evidence-based treatments for children and their families.
Of all these domains, executive functions are of particular interest, given their protracted development and the key role they play with respect to the effective acquisition of new skills and knowledge and the application of this knowledge to the child's real world. Executive function is now a well-established concept and incorporates those skills necessary for purposeful, goal-directed activity. Recently the scope of executive functions has been extended to include affective or ‘hot’ executive skills (e.g. theory of mind, social skills) as well as the more traditional cognitive or ‘cold’ skills (e.g. planning, attentional control, cognitive flexibility). Evidence suggests that, in adults at least, these skills are largely mediated by the frontal and prefrontal cortices of the brain, providing conscious direction to the posterior functional systems for efficient processing of information in novel, problem-solving situations. Importantly, these frontal regions are relatively immature during childhood, with development thought to be a protracted process continuing into late adolescence and early adulthood. While the frontal underpinnings of executive function are less clearly defined in children, these regions clearly play a key role in the development of such skills.
As executive functions develop throughout childhood, it is likely that progress and mastery of such skills may be disrupted due to early childhood insult. Such disruption may interfere with the child's capacity to develop normally and interact effectively with the environment, thus leading to ongoing cognitive, academic and social disturbances. While clinical case studies have provided anecdotal evidence of problems in planning, problem-solving and abstract thinking in the day-to-day lives of these children, such ‘executive dysfunction’ is often difficult to detect using traditional assessment tools. In fact, both clinical practice and research endeavours continue to be limited by a lack of developmentally appropriate and ecologically sensitive assessment tools.
Executive difficulties have also been argued to limit the child's ability to benefit from intervention and treatment, with suggestions from the adult literature that such impairments will result in a failure to generalize rehabilitation strategies to real life situations. Such arguments have been difficult to counter in the paediatric domain, given the complexities of conducting intervention research with children. Of the small number of published studies, many are limited by small sample size, lack of appropriate controls and ecologically valid outcome measures. Research methods of highest standard, such as randomized control trials, are plagued by practical problems such as the low base rate of early brain insult, and poor child and family adherence due to time factors, family and work commitments and school timetables.
In considering the best focus for a special issue on the frontal lobes, executive function and rehabilitation from childhood brain insult, the aim was to provide some dialogue across the disparate disciplines contributing to the field. We believe that future progress will be dependent upon collaborative approaches, where clinical researchers, laboratory scientists, health professionals, educators and families share their knowledge and experience to develop a more 'holistic’ approach to improving the health and quality of life of these children. To this end, contributing authors were asked to look outside their specific fields and to consider how their methods and results might be applied to design more effective and empirically driven intervention methods with the aim of enhancing quality of life for children and families.
In this special issue of Developmental Rehabilitation, a series of papers was collated, focused on the frontal lobes and executive function and representing recent advances across a range of disciplines and research methods. We believe these demonstrate the breath of the research necessary to advance the field of early brain insult. Contributions include animals studies (Halliwell et al.; Giza et al.), which have the advantage of being able to carefully control confounding factors, such as insult characteristics and environment, to facilitate our understanding of recovery patterns and outcomes following childhood brain insult. Spencer-Smith and Anderson provide a review of development of the frontal lobes and executive functions, a knowledge base critical to accurately differentiating normal from impaired skills due to early brain insult. Thompson et al. report on a single case study which illustrates the richness of such methods and their capacity to progress one's understanding of the natural history of frontal insults and the complex processes of neural recovery. There follow several empirical papers, which employ group-based designs and address complex and controversial questions, including the relationship between specific executive skills and social and emotional outcomes (Tonks et al.; Levin et al.), injury-based predictors of executive deficits (Maillard-Wermelinger et al.) and appropriate methods for assessing ecological aspects of executive function (Beddell). The final set of papers are focused on intervention and rehabilitation (Galvin and Mandalis; Catroppa and Anderson; Ylivasaker and Feeney) and demonstrate how empirical knowledge in the field can be applied to improve treatment and optimize quality of life in children with early brain insult.
In conclusion, as this special issue was finalized, my co-editor, Mark Ylivasaker, lost his long and incredibly brave fight with cancer. Those of you working with children with brain injury will be well aware of Mark's significant contribution to the field. Over his outstanding career he established himself as an international leader. His work has been trail blazing on many levels and in an area replete with challenges. He will be remembered for his insistence on theoretical principles, his empathy and understanding of his clients, his determination to establish a strong evidence base for cognitive rehabilitation and to disseminate it effectively to health professionals for the benefit of children with brain injury and his enthusiasm and generosity for teaching and mentoring. Mark has been a great friend, colleague and inspiration and his work will continue to guide this discipline into the future.