ABSTRACT
At the time of a traumatic brain injury (TBI) a complex array of factors converge to contribute to recovery or the lasting cognitive and neuro-behavioral effects of the injury (Tucker, 2005). Since TBI is an acquired injury, a brain's “health” and overall functional integrity at the time of injury should be key factors in the ultimate effects of the injury. In this context, two obvious factors that relate to outcome are a brain's ability to withstand the initial injury (i.e., protective factors) and its capacity for repair and recovery (i.e., recuperative or promoting factors of healing and adaptation). Such factors relate to a given brain's reserve capacity first to withstand the injury and then to repair itself and potentially recover. Within each general factor are hosts of potential contributing factors that, at any given time, may influence outcome. “Protective” factors were first observed early in the course of animal brain-behavior research, three-quarters of a century ago (see Schulkin, 1989). It was noted that prior to surgical ablation of a given brain structure, pre-surgical experience made a difference in outcome (Schulkin, 1989). Evidently, the amount and type of functional neural networks in place at the time of injury have a bearing on outcome. From a developmental perspective, complex interactions between experience and neural development lead to overall brain development. Therefore, the interaction of neural growth, experience, and the timing and mastery of cognitive abilities relates to optimal brain function at any given point in life. If these factors are important in brain development for a given brain to reach optimal levels of function, they are likely also to be important for how a brain responds and recovers when injured. In fact, although not coined in terms of contemporary theories of “cognitive reserve,” this was notably part of Karl Lashley's (1950) quest more than 70 years ago in his search for the “engram,” the neural locus of memory. At the conclusion of this chapter, the concepts introduced by Lashley are revisited in light of contemporary methods of neuroimaging analysis, cognitive reserve theory, and acquired brain injury.
