IS IT REALLY BETTER TO HAVE YOUR BRAIN LESION EARLY - REVISION OF THE KENNARD PRINCIPLE

Redirected growth of the optic tract in hamsters with lesions of the midbrain tectum at birth results in anomalous retinal projections with correlated functional effects; these include a sparing of visually elicited turning responses which are lost after comparable lesions in adulthood. However, the animals sometimes overshoot or undershoot the target, and the responses are slow to be completed. In cases of early unilateral lesions, an optic tract projection to the wrong side of the midbrain is correlated with turning in the wrong direction in response to stimuli in specific locations. These misdirected movements can be enhanced by reward or suppressed by non-reward, or abolished by surgical section of the abnormal pathway in the mature animal. Principles derived from the experiments with animals allow us to predict that specific lesions in fetal and neonatal humans will cause particular patterns of altered growth of neuroanatomical pathways. These alterations can be expected to cause behavioral anomalies, not only in sensorimotor functions, but also in cognitive functions and in emotional responses and expression; some neuropsychological findings can be interpreted in this manner. © 1979.