Traffic accidents typically cause a very different sort of brain damage than strokes. As we have seen, strokes tend to affect mainly the brain areas responsible for moving various parts of the body, speaking and understanding language, or some types of memory, as these are the areas most readily damaged by interference with their blood supply. Traffic accidents, in contrast, generally cause injury to the front of the head, as it impacts some hard, unyielding part of the vehicle. This results in damage to the frontal areas of the brain, the parts that are responsible for what are called 'executive functions,' such as setting long-term goals, seeking out problems that need to be solved, and planning how to solve them.
brain damage can be hard to assess in the usual tests designed to measure intellectual performance in ordinary people, such as IQ tests. When patients with frontal damage are given these tests, they often do very well. This is because the areas of the brain that are involved in answering questions or solving problems once they have been presented are not damaged. Let's say Zachary learned how to solve simple algebraic problems at the age of 13, and when he is 17 he is involved in a car accident that damages his frontal lobes. If the neuropsychologist testing Zachary's functioning after the accident gives him the sort of algebraic problem he knows how to solve, he may do very well, as the areas involved in solving such problems were not damaged in the accident.
Indeed, Zachary may have no trouble with any part of the IQ test, but if he is sent home he may simply stare at the wall or the television set all day without ever trying to do anything. This is because the part of his brain that has been damaged is the part that chooses what to do next and orders this choice to be carried out by the other parts of the brain, so he can't do anything on his own; he can only respond to the requests or orders of other people.
If Zachary's father, seeing this problem, then takes him to a rehabilitation center, they will have a hard job trying to help him. Such patients, in general, are much harder to rehabilitate than those who have lost the ability to walk or speak or write. This may be due to a problem similar to the one we discussed in the case of temporary memory. The executive functions may also be stored in only one set of connections, making it very difficult for the brain to set up a detour around them so as to regain its proper functioning.
Why should this be? Why should it be possible to relearn to use one's hands after a stroke, say, but not to plan one's future activities? Why should there be alternate, although little-used, pathways for writing, which can be strengthened by practice after the major pathway has been damaged, while there are no such alternate routes for planning one's activities?
Pathway interference
It seems to me that the reason for this difference is the problem of interference. It doesn't hurt to have several different pathways for writing because they don't interfere with one another. I can print in upper and lower case letters, I can print all in capitals or all in lower case, I can write cursively in a very neat way, I can write very sloppily, I can write in large letters with chalk on a blackboard, I can write in tiny letters if all I have is a small piece of paper. At any one time I choose the way of writing appropriate to the current situation, and the fact that I have all these other alternatives does not interfere; I can just ignore them. Thus if a stroke should damage the area which contains these writing pathways, there is a good chance that some of the pathways will be less damaged than others, since there are quite a few of them. Even if the main pathway is no longer usable, so that the patient cannot write at first, practice can strengthen one of the other, little-used pathways, to enable the recovering patient to learn how to write again.
But the situation is very different where planning one's activities is concerned. If there were alternate pathways for planning, I might plan two different acts for the same moment, and the result would be chaos. I'm not talking about the ordinary slipup where I make an appointment to go to the dentist on Tuesday at 10:00, and then, totally forgetting about it, make an appointment for the washing-machine repairman to come at the same time. This occurs because I wasn't thinking about the dentist appointment at the time when I made the appointment with the repairman. These are two activities which involve very different aspects of my life, and so I'm unlikely to be thinking about one when I'm thinking about the other. The two appointments are stored in two different parts of my temporary memory, each of which is connected with a different permanent memory network. Therefore there are no direct connections between them, and so outside help is necessary for co-ordinating them. Indeed, this is why appointment books (whether paper or electronic) were invented.
What I am trying to explain here is the need to avoid a situation which is hard even to imagine. Let's use a simple example. I am reaching for the coffee cup on the table, but the cup is behind my orange-juice glass, so I can't just pull the cup towards me unthinkingly, without any advance planning. Two possible ways for me to get the cup would be to reach around the glass and bring the cup to the front of the table in a circular motion, or to move the glass out of the way and then bring the cup directly towards myself. What is important here is not which choice I make, but that I should choose only one. If I had two parallel pathways for the process of choosing which one of these simple everyday acts to perform, then one pathway could be choosing one move while the other one was choosing the alternative move. Since these parallel pathways would be activated at the same time, they would send conflicting messages to my arm, and either I would end up doing nothing, or, more likely, I would knock over both the glass and the cup, so that the table, the floor and my clothes would be covered with orange juice and coffee.
The same problem would arise when I tried to write, if I had not only several writing styles to choose from but also more than one pathway for making the choice. It is certainly an advantage to be able to choose a small handwriting when I have nothing but a little piece of paper to write on, or a large handwriting to make the words on the blackboard visible to a large class. But if both alternatives were activated at the same time, I would be making the strokes for the large and the small letters in some random order, and the result would be totally illegible.
The pathways involved in choosing a career plan for the next stage of my life are undoubtedly much more complicated, but again, no matter how many alternatives I can think of, I must be able to choose one of them in the end. I cannot pursue a career as a doctor and as a lawyer at the same time; I have to choose and act upon one of these possible alternatives. This is probably the reason why there can be only one pathway for choosing which plan to carry out, and thus it can explain why there may be no way of compensating for it when it is damaged. There can be no detours here; there has to be one point where decisions are made, where action is initiated, and so if this pathway is damaged, nothing can replace it.
