suggests that those with SMC may be working harder to obtain the same level of
performance as those without such complaints. The larger literature on SMC in
older adultsfinds that when detailed questions or validated questionnaires are used
to assess SMC and comprehensive batteries are used to assess cognitive function,
SMC do reflect objective performance and there is specificity to types of SMC. This
is supported by imaging studies that reveal that those with SMC show changes in
brain structure and function.
The answer to the question“Do SMC reflect a decline from prior levels of
function or predict future decline?”is similarly complicated. When a single or few
questions are used to assess SMC, SMC are related to decline in objective cognitive
performance over time. When validated questionnaires are used to measure SMC,
the data are more equivocal, with some studies showing SMC predicting later
decline, and others not. The data on whether SMC reflect decline from prior levels
of objective function are also equivocal. In contrast, longitudinal studies—which
have the stronger research design—almost universally find that baseline SMC
predict later cognitive impairment or dementia. However, baseline cognitive status
may moderate this relationship, as one study found this relationship only in those
who were cognitively impaired at baseline, and another, only in those that were
cognitively normal.
Multiple methodological issues might account for these disparatefindings. The
first concerns how SMC are ascertained. The questions“How is your memory?”,
“Do you have memory problems?”, and“Do you consider yourself as being for-
getful?”each assess global memory function but are not necessarily interchange-
able; one can be somewhat forgetful but not view this as problematic for daily
function or abnormal for age. Ratings of current memory compared to earlier in life
versus compared to same aged peers also tap into somewhat different aspects of
memory function. General ratings of memory may differ from frequency ratings for
problems in daily activities, or the weight given to these problems, or the amount of
worry these problems might cause. The use of validated questionnaires is one way
to address this problem; however, questionnaires vary in their factor structures, and
studies have not uniformly analyzed each subscale in relationship to objective
performance. Further, several studies have used a sum total score. Severity, fre-
quency, and type of complaint are all important dimensions that need to be further
investigated. Another issue is what is meant by“memory.”For the layperson,
“memory”is often viewed as a uniform construct, whereas cognitive scientists
recognize that it is multifaceted, relying on attention, executive, and retentive
memory functions and differing across modalities (verbal, nonverbal, tactile).
Difficulties with encoding, storage, or retrieval can each be thought of as evidence
of forgetfulness but reflect very different brain structures and functions. Much more
work is needed to separate out specific cognitive complaints (such as word-finding
difficulties, problems with multitasking, and inattention) and relating these to
specific objective measures of cognition. A third issue concerns the types of cog-
nitive assessments used. Many studies have used a limited cognitive battery; others
have assessed memory with insensitive tests. As SMC often relate to other
non-mnemonic cognitive domains, it is important to use comprehensive cognitive
13 Subjective Memory Complaints and Objective Memory Performance 293