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. (to be continued on page (2) 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.