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Alzheimers Disease and other Cognitive Disorders

Dementia: What Gets Damaged; What Gets Saved

Mark Dombeck, Ph.D.

elderly couple on park bench by a lakeA woman in her mid 60s comes into my clinic for a depression screening. As I interview her, I notice something odd about her manner. She's repeating herself. So I start to ask her questions about her past, and then ask the questions again to see how she responds. She is able to describe aspects of her life from 30 years before with remarkable clarity. However, she doesn't seem aware that I've been asking the same questions about her past multiple times, each repeat occurring in ever shorter intervals. Every time I ask, she launches into her story with fresh vigor as though telling me for the first time. I realize that, though this woman has little difficulty remembering the distant past, she has a significant memory problem known as anteriograde amnesia; a condition characterized by her inability to create new memories so as to remember new things happening in the present. Anteriograde amnesia is the opposite of the other sort of amnesia that most people are familiar with, retrograde amnesia, which is the type where people forget their past."

Towards the end of my interview with this amnesic woman it occurs to me that she has arrived at the appointment alone by way of city bus. Though she needed to make several complex connections to get to the clinic, she has navigated just fine, despite the fact that she cannot form new memories very well.

I'm on the wing of a nursing unit in a local hospital there to do neuropsychological screening on a patient who has apparently been driving the nursing staff crazy. The man I find is confined to a wheelchair, but for all that is quite muscular and mobile. The problem is that he keeps rolling his wheelchair into the hallway and stranding himself there in the path of foot traffic. My testing reveals that the guy has profound spatial processing difficulties in addition to other issues. Probably because of a brain disease issue, the man has lost his ability to easily navigate space; to understand right from left and near from far. It's no wonder that he keeps stranding his chair in the hallway; he can't tell where he is going or how to get back where he started. The damage to this man's spatial navigation abilities is also invisible to him; he has not noticed that it is gone so he can't tell anyone about it. The problem is invisible to the nurses too. They just think he's just being oppositional. They haven't realized that there are brain problems at work. I explain the situation to them in a short consultation meeting before I leave so that, hopefully, they can find some extra compassion for the guy.

An older woman I know has significant medical problems, including diabetes and heart disease and went through a rather severe medical crisis a few years back. For a while it looked like she might not make it, but to the delight of her family she did emerge from her crisis, now wheelchair bound and unable to live independently anymore but still quite alive. Her lack of independence is not simply due to her needing a wheelchair for mobility. She has been cognitively compromised as a result of her illnesses. Her personality has changed as well. Where before she was a rather vivacious lady, she is now compliant and childlike. She is far less able to communicate than before her crisis. When you interact with her, there is a sense about her that she is not totally there anymore. You aren't even sure if she remembers who you are all the time or is just faking it to save face.

All of the above are cases of Dementia

These stories illustrate cases of Dementia, a diagnosis characterized by memory loss of varying types and other cognitive deficits that interfere with people's ability to speak, move, identify things, concentrate, pay attention, remember things, solve problems and form accurate judgments. Significant cognitive problems such as these are caused by brain damage where some of the living tissues in the brain are damaged. Enough damage occurs in specific places in the brain to cause particular cognitive problems, but not enough occurs to cause a vegetative state or death.

Any cause of brain damage will suffice to cause dementia, but there are two common ways that such brain damage tends to occurs. The first is due to strokes and similar cardiovascular disease incidents, and the second is due to progressive brain diseases, the most well known of which is Alzheimer's disease. Cardiovascular events cause brain damage in an all-at-once manner. In the case of a stroke, a blood clot lodges in a narrowing blood vessel within the brain and cuts off the free flow of blood to downstream brain areas, depriving them of oxygen and food and thus starving them to death. In the case of Alzheimer's and similar progressive brain diseases the damage occurs gradually and progressively. The disease process involved in Alzheimer's Disease alters normal brain cells (neurons) in a gradual and progressive way so that over time they start filling up with plaques and tangles which are abnormal structures that gum up their ability to function normally. Affected neurons become unable to carry a signal properly and cease to work properly.

Critical Brain Areas

The lost of a single neuron is no big deal. However, the loss of many neurons is a very big deal. When enough neurons in critical brain areas become unable to function, that brain area stops being able to do its job and the mental faculties that are supported by that brain area stop being available.

It used to be thought by some that the brain was more or less undifferentiated, meaning that each part of the brain had the capacity to do jobs done by other parts of the brain; that no part was particularly specialized. Advances in neuropsychological research have conclusively debunked this belief. Today we know that the brain is highly modular in how it is structured, and that there are critical areas within the brain that are specialized to do particular jobs. If you damage a critical brain area enough, the brain will cease to be able to do the job that the damaged area was responsible for, and no other brain area will be able to compensate for it very well.

The hippocampus is one particularly important critical area which is responsible for laying down new memories. If you destroy someone's hippocampus you more or less destroy their ability to remember new things and may also limit their ability to retrieve old memories too. There are many other critical areas besides the hippocampus. The frontal brain is identified with what is know as executive functioning and makes for another good example. Damage to the frontal brain is associated with executive functioning deficits (described below).

What happens in dementia is that particular parts of the brain, including some critical areas, become damaged or die, but other parts of the brain remain alive and kicking. What emerges from this process is a person who has had some cognitive capabilities erased or dimmed, while others are left intact, hence my title "what gets damaged; what gets saved. The tragedy of dementia is, in some respects, that it is so partial and incomplete. It is a terrible thing to witness the loss of one's own abilities or to witness it occurring in others. Far better to either not sustain the damage in the first place or to be damaged enough that you don't know what has happened to you.

Mental Abilities Get Damaged

The cornerstone deficit that characterizes Dementia is memory problems. Not the run of the mill memory problems that people normally experience as they age, but more severe memory problems where old memories can no longer be recalled (retrograde amnesia) or new memories cannot be laid down (anteriograde amnesia). A diagnosis of dementia requires more than the presence of memory problems, however. At least one other significant cognitive deficit must also be present.

Besides memory disturbance, the common cognitive impairments associated with dementia are aphasia, apraxia, agnosia, and deficits of executive functioning. These terms respectively describe impairments of language, movement, knowledge and judgment. Because these terms are likely unfamiliar, I'll break them down so that they can be more easily understood.

  • Aphasia refers to language disturbance. When someone is aphasic, they are having difficulty using language to communicate. Depending on what parts of the brain are having difficulties, aphasic patients may have difficulty producing words (e.g., they may know what it is they want to say but struggle and strain to convey that meaning) or they may have no difficulty producing words but cannot manage to say anything meaningful, despite their best effort.


  • Apraxia refers to a loss of the ability to move one's self, and specifically to a loss of people's ability to initiate and carry out practiced movement sequences that used to be easy for them. Patients with apraxia may have difficulty walking, for instance, or shaving themselves or brushing their teeth. In dementia, these movement problems are not due to problems people are having with their limbs, muscles, bones and tendons, but instead are due to brain damage.


  • Agnosia refers to people's loss of the ability to identify people places and things. The most obvious way that agnosia presents itself is patients' impaired ability to come up with the name for common things like eye glasses or pens or cars. The loss of names for things is not so bad in of itself. However, when agnosia becomes more advanced, even friends and family's faces may no longer recognized as familiar; an outcome which is very much heartbreaking.


  • Executive functioning has to do with decision making abilities and judgment. Executive functions determine how well people are able to shift attention from one task to another or hold attention on one task for a length of time; an ability we call concentration. Executive functions are also vital with regard to how well people are able to delay gratification, even out their jagged moods, make plans in advance, and to make deliberate actions after first considering the likely consequences of various courses of action. People whose executive functions are disturbed may become highly emotional in an unrestrained and unpredictable manner. They may act impulsively and without forethought and do highly inappropriate things. They may have great difficulty concentrating, or show a tendency to fixate on things and only with the greatest effort be able to shift their attention away from that thing they are fixated upon.

In cases of dementia, these cognitive deficits are not temporary, but rather are more or less permanent in nature. They may wax and wane but they won't go away. Whether they will tend to get progressively worse over time is dependent on the cause of the brain damage that underlies the dementia. Brain damage caused by stroke is generally not progressive, because strokes are not progressive. They happen all at once, and the damage they cause occurs all at once. Dementias due to Alzheimer's disease, or other medical disorders such as HIV or Parkinson's disease, on the other hand do tend to be progressive in nature because the underlying disease processes causing them tend to get worse over time.

At least for now, most forms of brain damage are not reversible. Progressive forms of dementia can sometimes be slowed through the administration of various medications, but there are not any cures for the underlying causes just yet. More information about treatment of dementias can be found in our Alzheimer's and other Dementias topic center, for those who are interested.

But not all mental abilities ...

Though dementia is defined primarily by what aspects of cognitive functioning become damaged, it is helpful to remember that dementia is by its nature partial and incomplete. There are aspects of personality and character and abilities that stay remarkably preserved, though this can be a mixed blessing. Even as it is wonderful to recognize the continuity of the person through the difficulty of their illness, it is also very painful to see what gets lost along the way. To illustrate the point, I'll end this essay with another story.

I'm on rounds and we're visiting a locked unit within a nursing facility. Someone rings the doorbell and we are buzzed in, the door locking again behind us. Immediately ahead is the common room and nursing station. One wall has a curious device mounted to it. Upon inspection, I see that this is a colorful plastic toy-like thing that spin and make noise. Like the sort of thing that you'd mount over an infant's head so as to entertain and distract that infant, except here wall mounted and serving the same purpose. When a patient gets very distracted, he or she can sometimes be redirected to the device, which captures their attention and they forget about what they were concerned about. (Look! Shiny!).

Various patients are milling about or seated. The lead doctor I'm with introduces us to one of the patients. She is extremely gracious and smiles with her entire body as she reaches out to shake hands with us. "I'm very pleased to meet you all!", she exclaims. I have been briefed in advance and know that this woman has a fairly advanced case of Alzheimer's disease which has robbed her of many of her faculties. She has severe memory loss, for example and probably lives in a sort of bubble where there is no real future or past. But her social skills are preserved very well, I think. I wish I knew how to make people feel so welcome.

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