Memory Special Report
Mild Cognitive Impairment: article excerpted from The Johns Hopkins Memory Bulletin
Forgetfulness. It’s pretty much guaranteed to catch up with you at some point in time. You are in your 50s, 60s, 70s, or older when suddenly it seems that you’re “losing it.” The name of the movie you saw last week? Can’t remember. You grope for the title of a book you just finished reading yesterday. You find yourself standing in front of the open refrigerator door, wondering what you were looking for. At a party, you’ve been speaking to a man for 15 minutes; when your wife comes over, you start to introduce her but can’t remember the man’s name.
Embarrassing, to be sure. “Another senior moment,” you may mumble to yourself as you experience one of these minor mental setbacks. However, others have darker thoughts when their memory starts slipping: “I must be developing Alzheimer’s disease.” There’s another possibility.
Such instances of forgetfulness may be neither “senior moments” nor Alzheimer’s. Instead, these amnestic difficulties may signal mild cognitive impairment, or MCI, a subtle but usually measurable change in memory that many researchers see as a transitional state between the memory changes due to normal aging and the earliest indication of serious memory problems triggered by Alzheimer’s. With MCI, memory loss is more severe than would be expected in a person of a particular age and education level.
The good news is that the forgetfulness typical of normal aging is relatively minor—more of a nuisance more than anything else, and nothing to be concerned about. Nearly all of us take more time to learn and recall information as we age. This occurs because the transmission of nerve impulses between cells and across cell membranes (synapses) in the brain inevitably slows as we get older. The decline usually progresses almost imperceptibly, over several decades.
By midlife, most of us occasionally find ourselves staring blankly into a kitchen cupboard or dresser drawer trying to remember what we were after. Although some people fear the worst, these memory changes are not dementia —a significant loss of intellectual abilities (such as memory capacity) severe enough to interfere with social or occupational functioning.
Normal age-related memory changes usually involve a slight delay in getting access to a memory that is in your brain. That’s why you recall your acquaintance’s name five minutes later, and why you eventually remember why you went to the refrigerator. In fact, although just about everyone experiences some degree of age-related memory loss, only 1 out of 100 people in their 60s have dementia.
Dementia, and Alzheimer’s disease specifically, is a major concern for most people 60 and over. Granted, dementia is not a natural consequence of aging, but its incidence does, unfortunately, increase with age. People who reach age 85 have a 20 to 35 percent chance of developing some significant cognitive impairment.
We currently have several therapies for AD, and many more are in various stages of development. Neurological experts hope that the development of improved therapies will be paralleled by the development of diagnostic tests that can uncover cognitive impairment at its earliest stages, including MCI. We know that AD doesn’t have a sudden onset; by the time symptoms appear, the disease has probably been developing in the brain for some time. Some researchers believe that MCI could be the earliest manifestation of AD.
When does normal forgetfulness end and MCI begin? Unfortunately, the question is difficult to answer. Because MCI is of intense interest and a topic of ongoing research, and because there still is a great difference of opinion and controversy as to what constitutes MCI, Dr. Rabins (PVR) and Dr. Morris (JCM), two experts on dementia and MCI, offer their counsel on a spectrum of frequently asked questions about MCI.
Q. What happens to a person’s memory during the course of normal aging?
PVR: Memory is power. It allows us to navigate our way through the world, learning, storing, and retrieving bits of information that will allow us to safely differentiate friend from foe, tonic from poison. Memory helps us plot a safe course from point A to point B, and to and from all points in between, if we so desire.
Moreover, our memories define who we are. Philosophers and scientists alike have long recognized that our memories and our selves are interwoven; perhaps they are even one and the same. Memories link us with the things that make us happy and those that make us sad, the things we’ve accomplished and the things we hope to accomplish in the future.
Memory has been described as a warehouse of knowledge. Actually, however, there is no single location or central warehouse in your brain where all your memories are processed and then neatly stored. Thanks to the neuroscientists who have begun unlocking the many secrets of the brain over the past few decades, it is now recognized that all new ideas and past information are reviewed, analyzed, compared, and connected, allowing you to create integrated experiences. Representations of these episodes are then stored in the form of electrochemical changes and altered neural circuits in various parts of your brain.
It is not uncommon to think of memory as an abstraction—a compilation of sensations, feelings, thoughts, and images that are mysteriously called upon when needed. However, that abstraction has a clear, if not yet fully understood, physical basis. Our brains are composed of hundreds of billions of cells that encode our memories, making them available through communication fueled by chemical and electrical interactions.
What you learn and are able to remember depends on your ability to make associations, or mental linkages, among experiences, store them in an organized fashion, and then search for them efficiently when retrieval is needed. This involves the functioning of several brain regions, and the neurons (brain cells) within each one.
While memory loss is one of the earliest signs of AD and a host of other dementias, a major difference between “age-related memory loss” and dementia comes down to declarative memory, the aspect of memory that stores facts and events.
If you compared the memories of a group of normal 25-year-olds to a group of normal 75-year-olds, the memory changes in the older group would be quite modest. What is interesting is that declarative memory, or free recall, is what starts to wane, along with speed of retrieval.
For example, if I were to read aloud a list of ten words to the younger and older groups, wait three minutes, and then ask each person to repeat as many words as they could remember, the average 25-year-old would remember about 8.5 words, while the average 75-year-old would remember 7.5 words. Many researchers believe that this difference in declarative memory is due to the normal aging processes.
Here is what I find fascinating about memory: If, instead of asking the older people to spontaneously recall as many of the ten words they can, I gave them a piece of paper with the ten words written on it but mixed in with other words, and asked them to circle only the words I had read to them, they would get just as many words as their younger counterparts! Having a visual prompt seems to help overcome that change in free recall memory.
However, if the same word test were given to people suspected of having AD, the difference would be striking. After three minutes, some would recall two or three words. Others might ask what a list is. The difference in word recall between a normal aging person (7.5 words remembered) and someone with AD (0, 2, 3, or 4 words remembered) is huge, and it’s evident that a serious cognitive gulf exists between the two.
But what does it mean when an older person remembers five or six words instead of the expected 7.5? Are they are simply at the furthest extreme of age-related memory problems? Or, on the other hand, do they have the earliest form of AD, a stage we now call mild cognitive impairment? At this point, unfortunately, no one can say for sure.
Posted in Memory on June 15, 2008
