The four exciting chapters in this section show clearly that traumatic brain injury (TBI) is common across the lifespan, and that a number of general principles apply. For example, regardless of age of onset, uncomplicated mild TBI is typically associated with only transient sequelae but as injury severity increases, there are more significant and persistent morbidities in the survivors. In addition, behavioral and psychosocial sequelae tend to be relatively most concerning in the long run, even when cognitive impairments are not trivial. These chapters also illustrate that variation in age of onset of TBI is associated with important differences in pathophysiology as well as predictors of outcome. Those at the extremes of the age spectrum appear to be relatively most vulnerable to the effects of TBI, whereas the specific detrimental impact of prefrontal involvement has been established much more clearly in adult than in pediatric samples. Different age levels are also associated with distinct necessities to consider comorbid complicating factors, ranging from learning disability in children, to alcohol abuse in young adults, to hypertension and diabetes mellitus in the elderly.

It is evident from the preceding four chapters that a long-term developmental perspective is needed when considering the impact of TBI. When severe TBI affects children, some sequelae may not become fully manifest until many years post-injury, and there also is concern about the possible acceleration of onset of degenerative diseases in older adults who sustained severe TBI decades earlier.