Mild Cognitive Impairment: What's in a Name?

Corner and Bond (2006) raise a number of important conceptual issues related to the problems involved in defining mild cognitive impairment (MCI), differentiating it from normal aging, the definition of normal aging itself, and ethical issues surrounding the possible adverse effects of a diagnosis of MCI on the individuals thus described. It would seem that portentous ramifications are involved and that clarifying the conceptual issues would be of great value, not only to researchers but also to the ever-growing population of elderly people. In what follows, I address some of these issues further.

Problems of Definition and Measurement

One of the problems that the authors discuss at the outset of their article concerns what methods are appropriate for detecting those with MCI: "Neuropsychological tests alone do not discriminate between normal aged-related memory loss and MCI or dementia and clinical judgment remains central to diagnosis" (Corner and Bond 2006, 5). Of course, to be able to discriminate between normal aged-related memory problems and MCI, we must first be able to define the former. What exactly is normal? As the authors correctly point out, the term has different meanings, one being normative (usual), another being nonpathologic. Is it normal (usual) for some sort of breakdown to occur in brain systems as a function of increased age? If so, is there a threshold age below which the very same physiologic breakdown is unusual? Would such a threshold age, if one existed, be the same for everyone, regardless of genotype and the cumulative interactive effects of nutrition, health, and stress-related factors over a period of decades? In effect, is some sort of memory impairment part of the natural (usual) process of aging for some people at particular ages rather than for others? And exactly what does it mean to be mildly impaired in the cognitive domain?

Hogan and McKeith (2001) presented a working group's definition characterizing MCI such that people who complain about memory problems and who also provide objective evidence of such problems, yet who simultaneously display "normal general cognitive function and intact activities of daily living" (Hogan and McKeith 2001, 1131), should be identified and followed. Here again, however, we confront the problem of defining "normal general cognitive function" as well as "normal activities of daily living." Can one have normal general cognitive function without normal memory function? If so, what exactly constitutes general cognitive function and on what conceptual or theoretical basis is such a definition valid? Furthermore, what sort of memory function are we talking about? Memory can be said to involve a number of stages: encoding, storage, and retrieval. Retrieval can be of the explicit type (conscious recall or recognition of specific information) with which people with Alzheimer's disease (AD) often reveal deficits or of the implicit type (a change in behavior as a result of previous experience of which the person may have no conscious recollection) as demonstrated in people with AD (Knopman and Nissen 1987). That is, people with AD can display deficits in explicit memory functions without similar deficits simultaneously in implicit memory functions.

A partial answer to the question about memory loss in MCI may be found in the use of the Mini-Mental State Examination (MMSE; Folstein, Folstein, and McHugh 1975), originally intended to be used as a screening device, but employed more and more frequently as an outcome measure to assess cognitive decline as well as the efficacy of drug treatments. Although the examination purports to test orientation, registration, attention, calculation, recall, language (naming, repeating, reading, writing, three-stage command), and construction, a task analysis reveals that the test is not quite as "global" in the cognitive domain as it is purported to be. For example, ten of the maximum thirty points on the examination are earned for "orientation" in time and place. Yet, all of the questions in this section of the test require intact recall of the relevant information. For example, if a person is asked, "What day of the week is this?" and replies "I don't know," the...