COGNITIVE ASPECTS OF VESTIBULAR DISORDERS

COGNITIVE ASPECTS OF
VESTIBULAR DISORDERS
VEDA Conference - Portland, Oregon

The following is a transcript of a lecture by Kenneth Erickson, M.D., at a VEDA conference held in Portland, Oregon.

Patients and families, of course, have known for a long time that vestibular disorders bring about cognitive difficulties. Some psychologists and neurologists here in Portland for at least five years, crystallizing in the last two or three years, have now begun to recognize and study a number of cognitive disturbances associated with vestibular disorders.

COGNITIVE DISTURBANCES

What is meant by cognitive disturbances?

Cognitive disturbances involve a difficulty in basic mental operations such as memory, paying attention or focusing attention on something, and in prolonged concentration. They also involve shifting attention from one subject or idea to another. People with cognitive disturbances have trouble in perceiving accurate spatial relationships between objects, in comprehending or expressing language, and performing calculations, and in a number of other areas.

These are areas that psychologists routinely test when they are doing so-called neuro-psychological exams.

A brief run-through of the kind of cognitive dysfunctions that we know of in vestibular disorders would have to include the following areas:

First of all, vestibular patients exhibit a decreased ability to track two processes at once, something we usually take for granted.

This ability requires a rapid shifting of attention. A good example is when you are driving and you have one person approaching unexpectedly coming out of a left-hand lane and another car coming behind you unexpectedly on your right side. Suddenly there are two things that you need to monitor and pay attention to at the same time. This might have come easily to you at one time, but if you now have vestibular difficulties, it's very hard.

Another example is when you have conflicting emotions inside of you, if, for example, there are two different things you want to do at the same time. The sensation you feel is confusion. Because of your cognitive problems, you may find it very difficult to express that confusion.

These are only two concrete examples of a pervasive problem.

The second area of cognitive problems vestibular patients exhibit is difficulty in handling sequences. This includes a wide range of sequences. It pertains to the mixing up of words and syllables when you're speaking, to the transposing or reversing of letters or numbers, to having trouble tracking the flow of a normal conversation or the sequence of events in a story or article. All of those have been very frequent complaints of the vestibular patients that we see.

A third area would be decreased mental stamina. That speaks for itself. For a vestibular patient an hour or two of concentration is a special blessing, and most days 15 minutes of intellectual concentration is very fatiguing.

The fourth area involves decreased memory retrieval ability, the ability to pull out information from your long-term memory store reliably. You might hit it most of the time, but you do not have a reliable rate.

Number five is a decreased sense of internal certainty. This is a peculiar way to state it, but it is exceedingly accurate. Vestibular patients with on-going physical problems have a frustrating lack of closure. They lack that "ah-ha; I've got it now; I see the big picture." Or "that's what I was trying to remember; I know it's that." They lack that kind of certainty which measures an idea or a conversation or a social situation up against some internal "gold standard." Vestibular patients often lack internal certainty.

Finally, people with vestibular disorders experience a decreased ability to grasp the large whole concept. The ability to see the big picture or the forest for the trees is very elusive for someone with vestibular disorders.

MEMORY PROBLEMS

I'd like to discuss these areas but most specifically memory problems in vestibular disorders; for most people that I see the memory problem is the most pervasive and troubling one.

To begin with I'd like to address what is known about stages of memory.

Using human and animal studies, scientists have found out that there are varying distinct stages of memory, and these are tied in with distinct physical areas of the brain.

(We'll ignore sensory memory.)

Immediate memory is where I'd like to begin. This is the ability to hold a name or phone number in mind for up to 30 seconds and sort of juggle it around while you're walking over to the telephone. This kind of memory takes concentration, and if any of us, sick or well, are suddenly distracted by a small child or something, it may be gone. It is a very fragile store of memory, about 30 seconds long. If the phone number stays longer after distraction, that's because it's gotten into recent memory.

The recent memory area has to do with taking new information and recruiting it into long-term memory. This is a key area that many vestibular patients complain of.

Recent memory can be sub-grouped into declarative memory, which refers to information -- the sort of thing you'd pick up in a textbook or an article or a conversation -- and procedural memory, which refers to procedures -- how to do something. A number of vestibular patients have noted that procedures tend to come easier than pulling out facts. Thus if there's a logical sequence that they are familiar with from before their injury, and they can fit the new information into that sequence, they have less difficulty than with placing new non-sequential information into their memories.

These kinds of memory are located in different areas of the brain, just as are the immediate memory and the sensory memory.

Finally if you're successful, the long-term memory store is filled with the information you want and can remember. It goes into what is called remote memory, and that store of information and sequences is diffused throughout the brain.

The areas of the brain which are keys to memory are the temporal and frontal.

If we look at microscopic sections of the brain, we see our brain cells are tied together with an enormous amount of interconnections. This is particularly true in areas that are called "association areas."

That's a handy name because to remember things you have to form associations and pull them out by associations, and throughout the front part of the brain, throughout areas that are called tertiary in other parts of the brain, you have an enormous mass of interconnections between the brain cells.

Some brain cells have 100,000 connections to other brain cells. It's no wonder that we can store an enormous amount of information; some scientists think it may be limitless.

When we take a look in the deep areas of the brain, as though it were sliced in half, there are some structures that are very relevant to what I was just speaking about.

Immediate memory involves a part of the cortex that is traveling between where you hear and process your hearing and the front part of the brain where you speak. It's a kind of traveling loop from the hearing processing center, the auditory area, around through some fibers to the speaking area, (Broca's area). It is this area where strokes can impair the immediate memory ability enormously and very specifically. In some stroke victims, just that kind of memory gets affected.

Going on, recent memory, the one that allows us to store information for a long period of time, is housed in a couple of areas. It requires the ability to input the information, which is very much a frontal-lobe function connecting into deep structures.

Then there's a complex loop, that's been studied now for 45 to 50 years that allows memories to cement down over minutes to months. The hippocampus, the long banana-shaped organ on both sides is the key area that allows us to fix the information over weeks and months.

If there are strokes or other damage in this area, a person becomes virtually locked in time. They do not pick up any new information. They might sound very intelligent based on their old information, from before the stroke -- that's still there for them. They might sound very intelligent in terms of something you are just saying to them this instant, but if you ask them what we were talking about five minutes ago, or half an hour ago, that information is gone.

Now we speculate that this area, this entire area, is somehow affected in people with vestibular disorders because recent memory ability, the laying down of new information is very confounded and difficult, in comparison to their pre-accident or pre-surgery history.

Let's talk a few minutes about stages of information input and retrieval.

The input stage is called acquisition; you're acquiring information. The storage stage is called retention, the ability to retain over minutes or months or years. And the retrieval, the output stage, is called retrieval. The acquisition and retrieval stages I mentioned in this diagram involve the front part of that loop. They are very much a front executive function of the brain.

The whole frontal lobe of our brain is involved in all our planning, decision making, handling two things at the same time, problem solving, sticking to a task, mental stamina -- a lot of those things sound very similar to the areas I was pinpointing for vestibular disorders.

We don't understand how the vestibular apparatus links in so intimately with the frontal lobe in terms of the mental processes we see impaired. That is an unknown. It will be a very difficult area to study based on our present knowledge. It is potentially a fruitful area to study over future years,
however. In any event, the key problems in vestibular recall are the input and the output. I say this because the storage part, the retention part, is actually not so badly affected.

We know this because we are able to measure the storage component. You might call it the tape recorder. Memory retention involves the temporal lobe and can be measured by using so-called recognition tasks. In recognition tasks, the patient is simply asked, "have you seen this word in the last half hour or not?" Patients are given virtually everything but the answer. It's like a multiple-choice question.

With that level of assistance, people with vestibular disorders do exceedingly well. It is also frustratingly well because on standard psychological tests, a vestibular patient can look darn good. This adds to their feeling of invalidation. Doing well on those recognition tasks can make the patient and sometimes the examiner believe that the physical and chemical malfunction is all psychosomatic or hysterical.

But if the examiner takes it a step further and asks how good is a person at putting in the information and then without much help pulling it out (much more like real life), that's when we see significant problems.

SPECIAL TERMS

I've coined a few terms to discuss the problems that arise when specific kinds of tests are given to vestibular patients.

First of all, we find in the clinic that vestibular patients have a reduced channel capacity.

We all have a certain capacity to take in new information at a certain rate; we get used to being able to do and to do it at our own rate. We know when we are tired we'll be a little more poor at it, or when several things are coming at us at once it will be reduced, but we know what it feels like, and we're pretty comfortable with our rate. It's similar to a computer's capacity to process information at a certain speed.

This capacity is considerably reduced in the majority of patients we see in the clinic with vestibular disorders.

Another area bears on the sequencing of information. The ability to recall in what order we learned or heard or were exposed to information is crucial to later recalling it in a meaningful or useful way.

For reasons we don't fully understand, most vestibular patients find it very difficult to properly sequence information.

If they're presented with a task, like the one we use in our clinic to measure sequencing, the "divided attention recall test," where we break up the person's attention, we find our patients have real difficulty. This task is much more like real life than mere recognition tasks. We present a series of words to the person and, not only do they have to pull back the word that they saw a couple of words ago (so they're starting to have to reach back), but at the same time they're having to sort every new word into a category. So there's two different things going on at once, and they're also having to reach back and recall recent material.

How many of you with vestibular problems find it hard to track a conversation, especially if there's more than one person you're listening to converse? You find that it's real fuzzy trying to reach back and see where it was just going, much less the big task of tracking what's going on right now.

I would imagine that the majority of you have had that experience. Even extremely bright people who have vestibular problems have massive problems with this. It's also extremely fatiguing.

Thus the sequencing problem that shows up in tasks like this is unique. They can reach back, the people who have taken this test, and hold back some of that information, but they often reach back too far or too recently; it's as though the time tag, the ability to know just about when that word happened, is very loose or gone. We don't understand it, but it's exceedingly similar to a kind of problem seen in early Alzheimer's disease. It seems to indicate a loss of a kind of time setting or time tag.

Finally, the lack of internal conceptual validation, the "aha, I've got it" experience, the sense of being valid about what you're thinking, seeing the big picture, being sure you've accurately completed a detailed task, being certain you remembered the correct name or fact, having that satisfying feeling of "yep, that's the match," -- is frequently gone.

Even though the majority of people we test are darn smart in many ways, they lack this sense of rightness. The vestibular patients we see often do rather well on the standard kinds of psychological tests, but we find they have a real problem knowing they are right, inside. They may be right 90% of the time, but they don't have that internal satisfying feeling.

That's a difficult one to understand, but we know from studies done years ago of people with brain injury that deep areas in the front part of the brain from the deep thalamus out to the front part of the brain are very important for locking into a kind of "gold standard," matching your sense with what is somehow stored in the brain and knowing that you are right.

Again, it raises fascinating questions about is there some way when you're very young that the vestibular system is wired into this whole area. We have absolutely no way of knowing that at this time. We do know the vestibular system links with your visual system, and visual control is very much a frontal lobe function, but there is no real knowledge of other networks going into
these memory centers.

PRACTICAL RAMIFICATIONS

What are the practical ramifications of all these deficits that I've been describing?

The three areas of dysfunction I just listed -- the decreased channel capacity, the diminished sequencing ability, and that lack of the aha experience inside -- those three areas cause incredible difficulties with simple daily life functions.

Let's start with personal life, your home, your shopping, your social interactions, your family responsibilities. The above difficulties I've spoken of wreak havoc with your ability to function in any normal personal setting, from planning a menu to organizing your day's do list, to tracking your children's conversation.

There's an astonishing contrast between the ease which most of our patients remember encountering in social situations prior to their illness compared to the difficulty they feel now when they try to deal with more than one person at a time. Situations which seemed hum-drum when they were well now appear impossible.

Occupationally, any time-locked task that has to be done by a certain time obviously is going to be affected. We don't even have to go into the detail I've gone into to say that the fatigue that is felt causes great problems with those kind of tasks. But any task that requires tracking more than one train of thought at a time, like that of a receptionist answering phone calls and plugging them into the right message boxes and so forth would be dramatically impaired.

Finally psychiatric complications such as depression and anxiety are almost too obvious to mention. After this kind of alteration of your most basic habits of thought, it's hard to conceive of not experiencing anxiety, depression, and disappointment with yourself.

Even if you have a supportive family structure that understands the cognitive problems, you end up inside not getting that sense of satisfying "I'm doing what I should be doing."

That links with that certainty inside that I spoke about. Even when you're fatigued and vestibular and you know you put in a good day and have done the best you can, that internal lock that says "I know I did this, I can retrieve what I did today, I can look at the big picture, and I had a good day" is not there for most vestibular patients. That alone, even within a loving supportive family and with no financial problems, would create anxiety and depression.

PHYSICAL AND PSYCHOLOGICAL RELATIONSHIPS

Why do these kind of memory and functioning patterns exist among vestibular patients?

There are three very obvious factors that many psychologists will raise. Those of you who have seen psychologists may recognize these diagnoses. First, pain is bound to cause problems with concentration and depression. Second, anybody with as much fatigue as the vestibular patient experiences will have a lot of trouble. Finally, the depression ensuing from that and everything else affects people's attention span and concentration and memory.

So, those of you who have gone through psychological tests often end up with a psychologist telling you that you have a few problems with attention but you're above average IQ, and there's nothing much to worry about; in fact, on their tests you look pretty darn good. The things that they do see, the mild attention and concentration problems, are probably due to the pain, the fatigue, and the depression.

Well, the hypotheses that we have are somewhat different than that. We don't know that ours are correct, but they do not include the above. The reason that we don't explain the difficulty vestibular patients have as due to pain, fatigue and depression is that if you test people with pain, with fatigue and depression, they either don't have this pattern of difficulty or it's far milder.

If we test people with a lot of pain or depression or fatigue, they will do badly on a variety of attention and concentration tests. On those tests, however, vestibular patients may do pretty well. If, instead, we test using the tasks where we divide up the patient's attention between sorting words by category and pulling back recent words, we find that even when they're feeling stable and are not in much pain, on this one test vestibular patients perform badly.

Obviously common sense leads us to explore this further. We can only conclude that this kind of malfunction seems highly specific to most vestibular patients. Shortly we will have enough control patients to publish these findings.

Our hypothesis is that the reason you have this problem as a vestibular patient is that your brain stem is affected. The brain stem is a stalk connected to the spinal cord. There are nuclei located in the brain stem that attach to your balance system; they are also highly important for keeping your cortex, your thinking areas, alert and aroused and attentive.

Could it be that since you're constantly fighting the mismatch from your visual input and your disordered balance system that a very basic mechanism -- a mechanism that was developed as you learned to sit and crawl and that influenced how you later manipulated objects and then walked and spoke and thought, a mechanism that's taken for granted and built into very fundamental habits -- could it be that something that fundamental is being distorted? That the vestibular and visual disturbance interferes with nuclei functioning within the brain stem and thus interferes with your sequencing of information and impairs and reduces your channeling capacity?

It's an intriguing hypothesis, exceedingly difficult to test. Nevertheless it makes some sense, as anyone with a vestibular disorder can speak to. Basic problems with reading, watching letters transpose, problems with movement and the orienting to the environment -- these are manipulations of the environment that were learned at a very fundamental developmental stage.

Question: Can some of these problems be described as dyslexia?
Answer: Yes, these symptoms can be misunderstood as dyslexia, although dyslexia has some other components to it.

Question: Is this damage permanent? Will the brain cells die from not being used?
Answer: We have no way of finding out the physical damage. The MRI's (Magnetic Resonance Imaging scans) often look perfect. It's likely that your vestibular system is sending inaccurate information to other brain areas that don't know how to handle it and/or information that gets distorted at very elementary levels of functioning. Those basic functioning areas seem to need accurate information from the vestibular system to think.

TREATMENT

Can we fix it? That is a very complex question but obviously among the most important questions to ask. Our clinic, which has been doing some of these studies, is very dedicated to trying to improve these memory problems. We're up against the fatigue problem, which we can do little
about.

One of our goals is to try to teach people tricks or handy ways of remembering things that would help anybody walking around the streets, shorthand ways of remembering things using pictures and so forth.

We've discovered if the picture is highly dramatic and a movement-filled picture, patients become highly vestibular, and it interferes with the memory. So we have to train people to remove a lot of motion from their images. These tricks are one aspect of our work. Using them, we have seen some improvement, but not without effort and time and learning to make these strategies become automatic.

Increasing patients' stamina, allowing them to take in larger amounts of information is an area which we're highly interested in pushing. A couple of our patients have been able to move into that phase, and we see that slowly, again not without a lot of effort, the capacity to increase the amount is there. I have a guess that part of the reason for that improvement is that one is learning new habits -- is training him- or herself to think again. As a vestibular patient, you must learn to move around in a slightly different-sized intellectual room. As you learn, just as in physical vestibular therapy,
compensating becomes automatic. You become comfortable with that little basic mental operation and this one, and you don't have to be thinking consciously about every step.

These new automatic habits allow you to take in more.

Our goal is to train these habits so people can actually improve on their performance and feel the difference at home. Again it's confounded by the fluctuating symptoms of the vestibular condition, by depression, by stress, by all kinds of other things that enter into your memory and finally by the fatigue that is constantly there because of the mismatch of your vision and your balance system.

Nevertheless, those who have reached that stage do feel a sense of gratification, and that drives us on. Our own sense here in the clinic is that given enough time, people will develop these new habits. We hope that we're developing a mental operation therapy similar to the physical vestibular therapy. Because it's so much more subtle and abstract, we suspect it will be very slow going. We feel that the rewards are there, and we continue to be dedicated to exploring them.

THE FUTURE

To go on, then, after completing the initial study that I mentioned on the divided attention/recall test, we plan to do two studies in which we look at the channel capacity, the limit on taking on new information before suddenly the slate is wiped clean and none of it comes back.

We are asking what is the sequencing problem when it comes to memory. How can we get around it? How can we understand it? Can we actually find some interesting little patterns that might help compensate for its dysfunction?

Finally, later on, we hope to study this very intriguing difficulty with that sense of closure, of certainty, inside. I suspect it's a multi-faceted experience that requires five or six different things to come together.

Within all this, of course, we have to include studies of people with pain, but no vestibular problems, depression but no vestibular problems, fatigue and no vestibular problems, head injury and no vestibular problems. That allows us to control for some of those confounding variables that people now use to explain the problem.

QUESTIONS, ANSWERS

Question: Do other people have problems with getting the first part of a word and then losing the second part, or getting the first part of a sentence and losing the second part?

Answer: These are indeed very common difficulties among vestibular patients.

Question: What effects might medicine have?

Answer: Many of the medications for vestibular problems are sedatives, even the anti-histamines and pain medications have a sedating effect. These will have an effect on memory and concentration. Vestibular patients who need medication to control their symptoms are often caught between a rock and hard place -- the vestibular symptoms cause them cognitive difficulties, but if they medicate to control the symptoms, the medication causes cognitive problems.

Question: I have a problem with getting the general idea of articles when I'm reading. Is this common?.

Answer: Definitely. In our clinic, we work on sequence and memory aids, in order to break the material down into simpler steps -- breaking an article, say, into key points. If there are more than five or six, then you will have trouble. Even simple articles can seem very complex. You can break reading materials down into key points, but it's hard work. You need to pick things that are worth it to you. Otherwise you'll get too fatigued and discouraged.

Question: Why do we mis-read, even when we know we are misreading?

Answer: It's called a substitute syndrome. Vestibular patients experience the syndrome often; it's very frustrating. I don't know why it's so rampant in vestibular patients. Probably it's linked to underlying injury to the vestibular system that goes beyond the vertigo, etc. When we tested a patient who was no longer having vertigo and whose scores were rather impressive in other areas, this "mis-reading" syndrome still existed. We don't know why. We ask, is the perilymph fistula creating a direct problem different from the vertigo? We need a larger sample and controls to really say.

Question: Do you have any help for family members?

Answer: A vestibular dysfunction affects the whole family because it affects the patient's total life. Family members need help and understanding almost as much as the patient him- or herself. In the clinic, we include family members' perspectives because they can sometimes give clues to behavior that patients aren't aware of. We also do counseling with family members.