Plasticity is an intrinsic property of the central nervous system, reflecting its capacity to respond in a dynamic manner to the environment and experience via modification of neural circuitry. In the context of healthy development, plasticity is considered beneficial, facilitating adaptive change in response to environmental stimuli and enrichment, with research documenting establishment of new neural connections and modification to the mapping between neural activity and behaviour. Less is known about the impact of this plasticity in the context of the young, injured brain. This review seeks to explore plasticity processes in the context of early brain insult, taking into account historical perspectives and building on recent advances in knowledge regarding ongoing development and recovery following early brain insult, with a major emphasis on neurobehavioural domains. We were particularly interested to explore the way in which plasticity processes respond to early brain insult, the implications for functional recovery and how this literature contributes to the debate between localization of brain function and neural network models. To this end we have provided an overview of normal brain development, followed by a description of the biological mechanisms associated with the most common childhood brain insults, in order to explore an evidence base for considering the competing theoretical perspectives of early plasticity and early vulnerability. We then detail these theories and the way in which they contribute to our understanding of the consequences of early brain insult. Finally, we examine evidence that considers key factors (e.g. insult severity, age at insult, environment) that may act, either independently or synergistically, to influence recovery processes and ultimate outcome. We conclude that neither plasticity nor vulnerability theories are able to explain the range of functional outcomes from early brain insult. Rather, they represent extremes along a 'recovery continuum'. Where a child's outcome falls along this continuum depends on injury factors (severity, nature, age) and environmental influences (family, sociodemographic factors, interventions).

Until recently, the impact of early brain insult (EBI) has been considered to be less significant than for later brain injuries, consistent with the notion that the young brain is more flexible and able to reorganize in the context of brain insult. This study aimed to evaluate this notion by comparing cognitive and behavioural outcomes for children sustaining EBI at different times from gestation to late childhood. Children with focal brain insults were categorized according to timing of brain insult, represented by six developmental periods: (i) Congenital (n = 38): EBI: first-second trimester; (ii) Perinatal (n = 33); EBI: third trimester to 1 month post-natal; (iii) Infancy (n = 23): EBI: 2 months-2 years post-birth; (iv) Preschool (n = 19): EBI: 3-6 years; (v) Middle Childhood (n = 31): EBI: 7-9 years; and (vi) Late Childhood (n = 19): EBI: after age 10. Groups were similar with respect to injury and demographic factors. Children were assessed for intelligence, academic ability, everyday executive function and behaviour. Results showed that children with EBI were at increased risk for impairment in all domains assessed. Furthermore, children sustaining EBI before age 2 years recorded global and significant cognitive deficits, while children with later EBI performed closer to normal expectations, suggesting a linear association between age at insult and outcome. In contrast, for behaviour, children with EBI from 7 to 9 years performed worse than those with EBI from 3 to 6 years, and more like those with younger insults, suggesting that not all functions share the same pattern of vulnerability with respect to age at insult.