"Exuberant" Neuronal Growth After Brain Damage in Adult Rats:The Essential Role of Behavioral Experience

Traditional investigations of the neural basis of recovery of function after brain damage frequently involve an analysis of behavioral recovery and of potentially related neural changes that might mediate the recovery. We recently have taken a quite different approach. Instead of assuming that the neural changes mediate (or permit) the behavioral, we showed that the opposite can be true: that behavioral events are absolutely necessary for the neural changes to take place /7-9/. These studies, reviewed below, have led us further to hypothesize that brain damage can sensitize, or prepare, remaining neural tissue through growth promoting and pruning-like mechanisms so that in the presence of appropriate behavioral pressure, the tissue can be drastically altered to compensate for lost function. In this scheme, (a) the neural events not only require behavioral experience (usedependency), but (b) even with extensive behavioral experience, the neural changes may not be initiated unless there is also brain damage, and (c) there may be a sensitive period after the brain damage occurs during which the behavioral experience can maximally modify the neural events.