The current study extends the available norms on a comprehensive battery of neuropsychological tests to people 90 years and older. Data on 10 widely available and well established neuropsychological instruments were collected from over 300 nondemented individuals in this age group. These tests span seven cognitive domains (i.e., global cognition, language, recent memory, executive function, psychomotor speed, visual-spatial ability, and attention/working memory) commonly impaired in AD and other dementias. We made considerable effort to keep total administration time fairly short (approximately 1 hour), minimize fatigue, and compensate for any sensory losses in vision and hearing that might compromise performance. Overall, the oldest old participants received the battery favorably.
The number of individuals in this study is considerably larger than that in other published normative studies. A comprehensive review (Mitrushina, Boone, & D'Elia, 1999
) of the existing normative data for many commonly utilized neuropsychological instruments included six tests in the current battery (BNT, Verbal Fluency, CVLT, TMT A & B, Clock Drawing Test). Without exception, reviewed studies had small samples of the oldest old. For example, of 24 studies evaluating the TMT, only two studies included individuals 90 years and older. Moreover each of these studies included only a few individuals in this age range: 21 participants aged 85–94 (Ivnik et al., 1996
) and 50 participants aged 81–91 (Richardson & Marottoli, 1996
). Another study on older adults (age range 62–95 years) residing in retirement villages and hostels in Australia gathered normative data for several neuropsychological tests (Anstey, Matters, Brown, & Lord, 2000
). However, the number of participants in the oldest age range (90–95) was very small; at most 23 individuals over 90 years of age contributed data for any given instrument. Thus, the numbers of 90+ participants have been too small to generalize findings.
Individuals' scores on the neuropsychological tests in the present study were influenced by age, gender, education, and affective state. Performance decreased significantly with increasing age on approximately two thirds of the tests in the battery—namely, the MMSE, 3MS, BNT, Animal Fluency, CVLT, TMT Parts A and B, Clock Drawing Test, and Digit Span Backwards. Thus, advancing age affected test scores in all domains. Women had better performance on the CVLT, MMSE, and TMT A. Despite a relatively narrow range of education in this sample, individuals with more schooling significantly outperformed their less educated peers on the 3MS, BNT, Animal and Letter Fluency, and Clock Drawing tests.
In the current investigation, participants with four or more depressive symptoms on the GDS had lower scores on the 3MS, Animal Fluency, and Clock Drawing. This suggests that mood may affect cognitive performance in the oldest old. However, the cross-sectional design of our study and our use of a brief screening instrument that provided a measure of depressive symptoms rather than a comprehensive psychiatric evaluation limit definitive conclusions. Furthermore, other studies present conflicting results of the relation between depression and neuropsychological functioning in the oldest old. Palsson, Johansson, Berg, and Skoog (2000)
reported a poorer cognitive performance in depressed versus nondepressed oldest old participants, whereas Backman, Hassing, Forsell, and Viitanen (1996)
did not find an association between level of depression and neuropsychological functioning. Given the mixed results across studies, the effects of depression in the oldest old age group need to be studied using larger and more diverse samples that include formal mood and cognitive evaluations.
Despite our best efforts to design a battery of neuropsychological measures appropriate for use with the oldest old, some of the participants were not able to complete all 10 tests. Since individuals with any comorbidity including visual or hearing impairments were not excluded, participants may not have been able to complete specific tests. Approximately 37% of nondemented 90+ participants failed to complete TMT A, TMT B, or both despite these tests being positioned halfway through the battery. Problems with visual disabilities (11%), fatigue (8%), and lack of time (10%) accounted for much of the missing data in TMT B, but a significant number of participants either refused to do the test (7%) or failed to complete it for other reasons (3%). Since the TMT A and B measure executive functioning, this may represent a significant decline in frontal lobe function associated with extreme aging. It is interesting to note that we did not see a similar effect of age on TMT C, which primarily measures motor speed. Also, as apparent in Table 5, individuals who completed specific tests demonstrated higher levels of cognitive performance as measured by both the MMSE and the 3MS than did individuals who failed to complete them. Lower global cognitive ability may be associated with failure to complete individual neuropsychological tests. For example, for TMT B 55% of noncompleters were CIND, while 45% of noncompleters were classified as normal. As individuals experience cognitive declines, they may be more likely to refuse or may experience fatigue more rapidly in the testing environment and be less likely to complete some components of the neuropsychological battery.
Norms for neuropsychological tests are useful to the extent that they can be generalized. To examine the representativeness of the 339 older participants in this study, we compared their demographic characteristics to those of individuals aged 90+ years in the general U.S. population. In the 2000 U.S. Census, the vast majority (89%) of the 90+ adults in the United States were Caucasian, with the remaining composed of 8.5% Black, 2% Asian, and 0.6% Native American or Inuit. A total of 76% of all 90+ year olds were female regardless of race. Thus, our sample largely reflects the current composition of the 90+ population in the U.S. Investigations in other ethnic/racial groups and in less educated populations will be needed particularly since these demographics are likely to change in the future.
In conclusion, this study describes a battery of neuropsychological tests selected and modified for use in very elderly adults. Strengths of the battery include its relative brevity, use of multiple well-established, widely utilized, and readily available instruments, and capacity to assess a broad range of cognitive domains. This study provides normative data for these neuropsychological tests from the largest group of individuals aged 90+ years published to date. These results provide a foundation for the evaluation of cognitive functioning in the rapidly growing number of individuals in their 10th decade and beyond.