Proving Invisible Injuries
A neuropsychologist's comprehensive neuropsychological evaluation will often be essential evidence of your client's current level of function and therefore the level of your client's harms and losses. In addition, I always sleep a little easier before trial if I also have a neurologist to testify about causation, even if the neurologist's own examination did not pick up the deficits identified by the neuropsychologist (a not uncommon occurrence in mild traumatic brain injury cases). In my opinion neuropsychologists are eminently qualified to testify about causation, but Courts tend to give a little more causation latitude to physicians so it is helpful to have one as part of your case.
But getting experts right is only the start of the process. In front of a jury, these cases often turn on lay witnesses - friends, family members, teachers, coaches, priests, etc... - who knew your client before and know your client now. This takes legwork. I do not think I have ever gotten everything I need from meetings in my office. The good stuff always comes when you are out at the client's home on a Saturday morning, watching firsthand how a neighbor now takes the kids to soccer practice because driving has gotten too hard for your client. Listen to a married couple explain how the dishes are never done at the end of the day, because sometimes the TBI victim who is at home with the kids needs to just sit in a dark room for long stretches. Look at the project in the garage that was started before the accident an d now will never, ever be finished. Look at the pictures of grandchildren, and really dig into whether your client can still do the same things with her grandchildren that she used to.
If you do this legwork, you will come up with more than you need. There's nothing wrong with that. Which witnesses are actually called to testify at trial can depend on a number of factors, and sometimes last-minute decisions. It is a good idea, for example, to consider the composition of your jury when deciding who you are going to call. If you have a couple of older jurors, then by all means call an older fact witness even (or maybe especially) if your client is young. The same is true of other demographic characteristics of your jury.
None of these witnesses need testify for very long at trial: at most a couple of quick, clear stories that illustrate how things were before and how they are now is more than sufficient. The stories they tell can be as compelling to juries as the most learned and detailed neuropsychological workup.