Neural plasticity and the K ennard principle: does it work for the preterm brain?

Summary  The K ennard principle suggests that the immature brain should be more able to recover from injury than the more developed brain. Curiously, preterm infants continue to have a high rate of debilitating neurodevelopmental handicaps despite a progressive improvement in structural damage to the brain, from acute necrotic injury of the periventricular white matter, with axonal loss in historical cohorts, to diffuse gliosis with trivial axonal damage.  In the present review we examine recent evidence that disability after preterm birth is largely mediated by disturbed development of neuronal connections. Potential mechanisms include impaired white matter maturation associated with gliosis, suboptimal neuronal maturation, adverse effects of infection/inflammation on the cell environment, exposure to clinical therapies that modulate brain function (including maternal glucocorticoids), upregulation of physiological apoptosis and loss or misprogramming of progenitor cells in the subventricular zone.  These findings suggest that insults during this critical phase alter the trajectory of brain development and that a key focus of basic science and clinical research should be to understand neuronal connectivity, as well as the triggers of cell death.