Executive function following focal frontal lobe lesions: impact of timing of lesion on outcome.

While it is generally agreed that outcome following cerebral insult during childhood differs from that seen following similar pathology in adulthood, the specific relationship between timing of cerebral lesion and outcome, and the mechanism associated with observed neurobehavioral changes, remains controversial. Data from children with focal lesions suggests a non-linear relationship between age at injury and language function (e.g., Bates et al., 1999). With respect to executive function, animal models also demonstrate a non-linear relationship, and suggest that outcome is tightly linked to underlying neuronal changes (e.g., Kolb et al., 2000). Whether these models easily translate to humans, where brain morphology, cognitive function and environmental influences are more complex, is not clear. To date, focal lesion research in children has been restricted to individual case studies or, to samples of children with lesions to regions subsuming language function, or those who have undergone hemispherectomy for the treatment of intractable epilepsy. This study aimed to build on current knowledge, investigating executive function in 38 children with focal lesions involving prefrontal cortex. Aetiology and timing of lesions was diverse. Results are consistent with animal research suggesting a non-linear relationship between age at injury and outcome, with "critical periods" during development when the frontal lobes are particularly vulnerable to insult, and others when outcome is more optimal. Our findings indicate that children with prenatal lesions are at greatest risk of neurobehavioral deficits. Children with lesions sustained in middle childhood demonstrate least severe impairments across executive domains, possibly due to a period of peak synaptogenesis and dendritic arborization during this developmental stage, in keeping with animal models and research investigating frontal lobe development.