As anyone who has worked in correctional psychology knows, head injuries are often the underlying cause of both cognitive deficits and behavioral difficulties in offenders (not to mention rampant ADHD). Both PsychCentral and Neurological Correlates have reviews of a really good article in the Wall Street Journal regarding recent research into the prevalence and impact of head injuries. According to the article, head injuries may be more common than originally thought, may have delayed impact in terms of symptoms (including cognitive deficits such as memory and attention problems, as well as other issues such as alcoholism), and may not be linked to the head injury, but rather seen as either a stand-alone mental health issue, or even lack of effort. Both PsychCentral and Neurological Correlates discuss their impression of the study.
To me, this isn't actually anything new, since it seems research has been heading in this direction in recent years. It's just nice that the data are so conclusive, so that the field can continue to seek out effective interventions. For years people discounted the impact of head injuries, especially closed head injuries such as concussions. Jokes regarding athletes getting their "bell rung" are fortunately becoming a thing of the past as recent examples (i.e. Steve Young ) have demonstrated that even mild concussions can have serious repercussions for future functioning.
In forensic psychology, we probably pay more attention to cognitive deficits and past head injuries than in general clinical psychology, since this is often the primary reason why a defendant is referred for a forensic evaluation (especially an evaluation for competency to stand trial). Nonetheless, obtaining an accurate history for head injuries is often difficult. Many individuals simply don't recall the head injury, since it may not have seemed like a big deal at the time. If medical attention was not sought, there will be no other record. In addition, if the injury was suffered some time ago, say in athletics, the impact may have been downplayed by both the athlete and/or the coaches. Also, one of the major symptoms of a head injury is a loss of memory, especially sequential recall - asking an individual to recall a perceived minor event that occurred up to 20+ years ago, who may well have some cognitive deficits, is not exactly going to get you the most accurate information.
The other problem is the seriousness of screening for a history of head injuries. Usually, in a general setting, an individual will be asked one, maybe two, questions regarding cognitive history. You'll usually get, "Have you ever suffered a head injury where you lost consciousness?" and, maybe, "Have you ever suffered a concussion?" That's it. If the person immediately answers "No," that's the end of it. Often, it takes individuals, especially those with cognitive deficits, to recall incidents like this. Multiple questions, from different angles, may trigger more efficient recall, and may also impress upon the client that what they initially considered a trivial "bump on the head" might have been more. After all, if the doctor is asking numerous questions, maybe it is more significant than previously thought.
Hopefully, ongoing research and articles like this will continue to impress upon both professionals and the general public that head injuries require a thorough assessment and follow-up monitoring. The trend is definitely in this direction, fortunately.