Decision strategies in neuropsychology II: Determination of age effects on neuropsychological performance

Archives of ClinicalNeuropsychology. Vol. 5, pp. 335-345, Printed in the USA. All rights reserved.

1990

0887.6177190 $3.00 + .oO Copyright 0 1990 National Academy of Neuropsychology

Decision Strategies in Neuropsychology Determination

II:

of Age Effects on

Neuropsychological

Performance

Charles J. Long and Kim Klein University

of Tennessee/Memphis State University

The relationship of age to neuropsychological test performance was explored on the subtests comprising the Halstead-Reitan Battery and allied tests. Performance of 192 pseudo-neurologic control patients across IO-year age intervals from I6 to 65 was analyzed. The findings indicate a strong age-performance effect on spatial and more complex integrative tests with peak performance between 25 to 35 years of age and a decline thereafter. A lack of significant decline was noted on sensory, motor, and language tasks. The findings reveal that there is a curvilinear change in performance as a function of age and were discussed with regard to the obvious need to modify decision strategies to account for the age of the patient.

There is clearly an age-performance relationship which influences the scores of most behavioral tests. This relationship is probably best established in standardized intellectual tests (Wechsler, 1955). If this relationship is significant with regard to intellectual tests, which are thought to be relatively stable measures of cognitive ability, then one must conclude that it will hold an equal or greater relationship with neuropsychological tests, selected because of their sensitivity to changes in cognitive functioning. An early study by Reitan (1955) demonstrated much higher negative correlations between age and neuropsychological test performance as measured by the Impairment Index for individuals over the age of 45. Further, this decline in older adults has often been equated to subjects with clinically established brain damage (Reed & Reitan, 1963a,b) or a history of alcohol

Reprint requests should be sent to Charles J. Long, Ph.D., phis State University, Memphis, TN 38152 335

Department

of Psychology,

Mem-

336

C. JS Long and K. Klein

abuse (Blusewicz, Dustman, Schenkenberg, & Beck, 1977). Despite this knowledge, age norms are not provided for the adult Halstead-Reitan Neuropsychological battery, and, thus, one set of norms must be applied to the entire population above age 15. In addition to the lack of age norms available for clinical use, research is further confounded by a general lack of information regarding age. Many studies fail to mention age of subjects or make comparisons across differing age groups (Parsons & Prigatano, 1978; Hevern, 1980). While age has frequently been considered in conducting research dealing with individual tests of the Halstead-Reitan Battery, only recently has attention been directed toward age effects on neuropsychological test battery performance (Benton, Eslinger, & Damasio, 1981; Bigler, Steinman, & Newton, 1981; Fromm-Auch & Yeudall, 1983; Goldstein & Shelly, 1981; Moehle & Long, 1984; Schaie & Strother, 1986). Many of these studies have been limited in scope and have often involved institutionalized groups. Some studies only investigated age to age 40 (Yeudall, Fromm, Reddon, & Stefanyk, 1986; Yeudall, Reddon, Gill, & Stepfanyk, 1987), others only 50 and above (Bak & Greene, 1980) or 65 and above (Benton, Eslinger, & Damasio, 1981). Thus, while age effects are considered, the restriction in range makes it difficult to evaluate possible decline in cognitive functioning thought to occur in the early 40-year age range. Age effect relationships were explored on the subtests comprising the Halstead-Reitan Battery for ages 15 to 64 by Fromm-Auch and Yeudall (1983). They investigated normal nonmedical controls and found age trends consistent with previous data indicating a decline in many cognitive functions. Another study investigated performance of pseudo-neurologic controls. Age groups were composed of patients referred for neuropsychological assessment by neurosurgeons and neurologists but whose subsequent diagnostic tests led to the conclusion that the patients did not have significant neurological involvement (pseudo-neurologic). Neuropsychological test findings from these patients were analyzed across ten year age intervals from 16 to 65 (Moehle & Long, 1984). The findings indicate a strong age-performance effect on certain neuropsychological tests with peak performance between 25 to 35 years of age and a decline thereafter. While age would be expected to effect performance on many neuropsychological tests, the effects of aging are not likely to be consistent across different abilities. Several studies examining the effects of aging on neuropsychological test performance have suggested that aging has the most deleterious effect on visuospatial performance (Shelton, Parsons, & Leber, 1982) or tasks which require the subject to engage in abstract reasoning, complex problem solving, memory consolidation, and learning new material (Reitan, 1967). These are functions which are also highly sensitive to the presence of brain impairment. In contrast, other abilities appear much more

Age Effects on ~europsycholog~ea~ Performance

337

resistant to the effects of aging. These include remote memory, language abilities, and elementary perceptual-motor skills (Lezak, 1983). Along with the normal decline in cognitive functions observed with aging, there is increasing evidence of structural abnormalities within the brain (Brody, 1970; Ordy & Brizzee, 1975). In order to determine whether the cognitive weaknesses experienced by an elderly person represent the effects of “normal” aging or the effects of organic brain impairment, it is necessary to have a clear understanding of the pattern of strengths and weaknesses observed with the normal aging process. Only after this goal is achieved will it be possible to determine the extent to which an individual’s performance differs from the normal aging pattern, and whether their deficits are greater than those expected in individuals of the same age. The purpose of the present study is twofold. First, the effects of aging on neuropsychological test performance for a group of pseudo-neurologic control patients was examined. Second, the pattern of decline associated with specific tests was investigated. It is hypothesized that performance on measures which rely heavily on new learning, problem solving, as well as more complex integrative tasks would demonstrate a more severe decline as a function of increasing age than measures of language related abilities, or simple sensory and motor tasks. METHOD Subjects The sample consisted of 192 subjects selected from a larger pool of 2500 patients who were primarily noninstitutionalized medical patients referred for neuropsychological testing by neurosurgeons and other physicians. Patients most frequently presented with complaints such as headaches, dizziness, or memory problems for which no physiological etiology could be found based on medical neurodiagnostic procedures. Although their symptoms may have been treated, the patients were determined to have no significant underlying neurological disorder. Individuals were excluded from the study if their history included head injury or any type of neurological disorder, psychiatric problems, or substance abuse. Subjects were administered the Minnesota Multiphasic Personality Inventory and were also excluded if this measure suggested that they were experiencing significant emotional distress at the time of assessment. Their actual performance on the Halstead-Reitan Test battery was not considered in group composition. Subjects were stratified by age into five groups: 15-25 (n = 43), 26-35 (n = 50), 3645 (n = 43), 46-55 (n = 30), and 56-65 (n = 27). No significant differences were found between the five age groups with respect to the demographic variables of sex, education, and Full Scale IQ (see Table 1).

z

Ed Sex Race occ FSIQ Suppr RT Agnos RT Graph RT Stere RT SP Percep Suppr LF Agnos LF Graph LF Stere LF Rhythm Tap RT

Age

N

Test Name

** * **

**

*

Sig

43 20.7 12.3 1.61 1.06 3.71 102.74 0.19 0.35 0.7 0.13 4.33 0.35 0.44 0.37 0.17 3.79 50.6

Mean 1

3.2 2.06 0.47 0.24 2.64 9.68 0.59 0.65 1.5 0.57 3.3 1.13 1.08 0.69 0.38 2.46 8.28

SD 1

Means and Standard

50

29.78 13.38 1.52 1 3.3 103.54 0.06 0.48 0.59 0.19 3.06 0.16 0.44 0.46 0.1 3.26 54.12 2.84 2.23 0.5 0 2.11 11.32 0.24 1.09 1.21 0.54 2.81 0.55 1.05 0.97 0.4 2.16 7.55

SD2 43 40.84 12.3 1.63 1.14 3.37 105.14 0.23 0.09 0.72 0.31 4.56 0.14 0.3 0.63 0.41 4.48 50.55 2.77 2.91 0.49 0.48 2.68 13.66 0.92 0.29 1.26 0.74 3.49 0.64 0.64 1.27 0.8 3.22 12.03

SD3

0.38 0.96 0.18 6.17 0.48 0.21 0.69 0.12 4.33 53.76

2.55 1105.97 0.07

I

30 50.8j 13.43 1.5

Mean 4

for All Neuropsychological

Mean 3

TABLE 1 for the Five Age Groups

Mean 2

Deviations SD4

2.83 3.17 0.51 0 1.96 13.56 0.38 0.94 1.69 0.39 4.08 1.22 0.49 1.07 0.33 2.97 6.17

Tests

27 60.74 13.4 1.52 1.09 4.04 107.15 0.38 0.79 1.5 0.64 6.52 0.35 0.65 1 0.76 5.56 46.46

Mean 5

3.15 2.68 0.51 0.3 3.32 15.04 0.8 1.31 1.98 0.74 4.81 0.85 0.98 1.57 0.89 3.21 9.81

SD5

Grip RT Tap LF Grip LF Trails C Trails A Trails B Crosses TPR T RT TPT B RT TPT T LF TPT B LF TPT T BO TPT B BO TPT T TO TPT B TO TPT MEM TPT LOC TH HFLU Aphasia

*** ** *** ***

*** *** *** ***

*** ***

**

35.02 45.33 32.33 32.13 27.61 59.36 2.7 7.11 9.93 4.32 10 2.28 10 11.71 28.4 7.74 5.61 53.68 2 2.08 18.72 2.11

1.36

8.67 12.11 12.86 11.22 19.47 1.86 11.71 0.46 1.97 0 1.17 0 5.2 7.03

11.44 43.06 48.6 37.92 31.61 28.32 64.62 2.41 5.61 9.96 4.03 10 2.22 10 11.34 29.96 7.1 4.9 57.09 1.42

15.84 7.11 14.05 18.12 8.92 21.72 0.81 3.24 0.28 1.55 0 0.96 0 3.83 0.28 1.45 2.11 24.88 2.3 38.81 46.52 35.14 29.3 34.21 75.51 2.69 5.36 9.14 4.5 9.81 2.98 10 12.87 28.79 7.21 3.91 54.87 2.57

15.2 7.65 14.51 13.63 12.39 25.73 1.16 1.99 1.14 2.2 0.88 1.55 0 4.64 5.32 1.41 1.95 16.97 2.48 2.82 52.35 2.7

40.25 48.79 34.14 31.8 34.38 82.34 2.85 6.62 8.75 6.05 9.21 4.38 9.68 15.69 24.07 15.4 5.36 15 12.71 12.71 29.08 0.82 2.32 2.4 2.5 1.81 1.98 1.36 7.7 11.23 1.63 1 .I9 16.26 3.21

36.04 41.46 33.65 42.5 44.04 102.96 2.96 7.13 8.96 6.44 8.85 4.66 9.48 17.89 26.56 6.15 2.85 47.83 2.38

12.21 8.29 13.03 18.72 22.27 63.43 0.86 2.17 2.36 2.64 2.46 2.66 1.65 6.79 8.22 1.51 1.79 20.27 2.86

C. J Long and K. Klein

340 Procedure

The test battery consisted of six measures from the Halstead-Reitan Neuropsychological Test Battery and allied procedures although the categories test was omitted (Table 1). An Impairment Index was calculated using the six Halstead-Reitan Battery measures and Trail Making Test Parts A and B. The tests were administered by trained examiners and the evaluation usually required approximately five hours to complete. The aphasia screening test was scored according to Russell, Neuringer, and Goldstein (1970). RESULTS The initial analysis involved examining the relationship between age and overall performance on neuropsychological measures as assessed by the subject’s Impairment Index. A univariate analysis of variance was performed to analyze differences between groups on the Impairment Index. These results demonstrated a significant decline in performance associated with increasing age, F(4, 188) = 1.688, p < .OOl. These data are shown in Figure 1. 50

40 u .-2 Ei E 0

30

P E ii z .3 I s

20

IO

0 1

2

3

4

5

Age Group

FIGURE 2=26-35;

1. Percent misclassified as impaired as a function 3=36-45; 4=46-55; 5=56-65).

of age (Age Group 1= 15-25 yrs;

Age Effects on Neuropsychological

341

Performance

Inspection of the data in Figure 1 indicate that performance is stable from 10 to 35 years of age with only 4% misclassification for each group. This increases to 20% for the 36 to 45 and the 46 to 55 year age groups. Finally, using the standard cutoffs, 41% of the subjects in the oldest age group were misclassified as impaired. The means and standard deviations for the various tests across the five age groups are depicted in Table 1. The next step in our analysis involved transforming all raw score data to standard scores using normative data from the 15 to 25 year age group, in order to compare the relative decline in performance of each individual subtest as a function of age. The resulting T-scores had a mean of 50 and a standard deviation of 10. Data were analyzed so that the T-scores above 50 indicated improvement. Initially, we plotted only the seven tests which comprise the Impairment Index and these data are shown in Figure 2. As depicted in the graph, performance on Trails B and TPT-Location show the sharpest decline with increasing age. A moderate decline in performance was observed on the Speech Perception and Rhythm tasks, while a significant linear decline was not observed on the Tapping task. After examining the effects of age on each individual test, it was then decided that it was equally important to represent those measures which appear resistent to the effects of aging, and for which no significant differences were demonstrated across age groups. No significant differences were found between the five age groups on any of the three sensory tasks (Suppressions, Finger agnosia, and Graphesthesia) for either hand. In addition, no significant differences were observed between the groups on the grip strength and motor sequencing tasks, or the Aphasia Screening Test and Thurstone Word Fluency Test. Tasks were then grouped as to whether they appeared to primarily assess motor, sensory, language, spatial, or integrative 70

1

60 -

40!. 0

I.

I

1

2

.

I, 3

+

TPT-Locaton

+

Trals

9

TPT-Time

+

Speech

-D-

TPT-Mempry

6

-D-

Rhythm

+-

TappIng

I

I

,

4

5

6

Per

Age Group

FIGURE 2. Standard scores for seven Halstead-Reitan tests as a function of age. (Standard Scores have a mean of 50, standard deviation of 10 with scores above 50 indicating performance below the mean).

342

C. .I Long and K. Klein

abilities. Each subject’s average motor score was computed as the mean standard score on the three psychmotor tasks, and the average sensory score was derived from their average standard score on the three sensory tasks. Similarly, the average language score was computed from the standard scores on the aphasia Screening Test and the Thurstone Word Fluency Test. Finally, the spatial score was derived from the subject’s standard scores on the TPT-Memory And TPTLocation tasks, and the integrative score was computed from each subject’s mean performance on Trails B and TPT-Total Time. These date are shown in Figure 3. As demonstrated in this figure, tasks which rely heavily on spatial and integrative abilities were most severely affected by increasing age. No significant differences were demonstrated between the groups on the average language score, and on the average sensory and motor scores, only the oldest group differed significantly from any other group.

DISCUSSION These results are consistent with previous studies which demonstrate a highly significant decline in neuropsychological test performance across certain functions associated with increasing age (Fromm-Auch & Yeudall, 1983; Reitan, 1955; Moehle, 1984). Our data indicate that if only one set of norms are used 20% of the 36 to 45 and 46 to 55 year age groups of pseudoneurologic controls would be misclassified. Furthermore, a remarkable 41% of the group between 56 and 65 years of age would be misclassified as brainimpaired on the basis of current norms. These findings are based on a modified impairment index which does not include the category test and the 70 -

401

0

1

4

2

5

6

Age Ck~p FIGURE 3. Average standard scores for five abilities as a function of age. (Standard Scores have a mean of 50, standard deviation of 10 with scores above 50 indicating performance below the mean).

Age Effects on Neuropsychologicd

Performance

343

results may behave differently from the traditional Impairment Index. Nevertheless, these data clearly suggest the need for standardized age norms in interpreting neuropsychological test performance. The decline in performance is clearly greatest for some spatial and more complex integrative tests such as TPT and Trails and no significant decline is noted with language tests. These findings are consistent with previous research (Schelton, Parson, & Leber, 1982; Reitan, 1967; Lezak, 1983). The lack of significant decline on sensory and motor tasks indicates that elementary sensory and motor skills are relatively stable (Lezak, 1983). There is a pattern in that tasks more sensitive to brain damage show the greatest decline with age. The current study employs a cross-sectional analysis to evaluate decline in cognitive functions as a function of age. Researchers interested in aging as the dependent variable, argue against the use of cross-sectional designs (Schaie, 1958; Schaie, Rosental, & Perlman, 1953) because there is a much greater decline than that found with longitudinal studies (Baily & Oden, 1955). They argue that cross-sectional studies fail to consider differences across generations (Schaie & Strother, 1968). While it has been argued that such a design reflects a greater rate of decline than longitudinal, consideration must be given to the question posed. If the process of aging is the main interest then longitudinal or cross-sequential methods may be more appropriate. However, the major focus of the present study is the investigation of age effects on neuropsychological performance as they influence clinical decisions. While older adults are further removed from formal education and represent different generation effects, this is, in fact, what must be considered in evaluating these patients. Because of these and many other factors, older adults may appear more impaired. In many respects the decision process demands cross-sectional data because older adults must be evaluated accurately based upon their current status at the time that they are evaluated. Only by controlling for the apparent decline in cognitive functions can accurate judgments be made. It may also be argued that normal controls or nonmedical subjects represent the ideal data base for comparison. However, the clinical neuropsychologist frequently evaluates patients referred by neurologists and neurosurgeons. The difficult decision is not choosing between brain-impaired and nonmedical controls but between brain-impaired and medical patients who subsequently undergo diagnostic tests which prove to be normal. It may be argued that performance of medical controls yields lower scores than nonmedical controls. While this is true (compare norms from this study with Fromm-Auch and Yeudall, 1983), the ultimate decision must be based on whether patients who undergo neuropsychological evaluation have significant cerebral dysfunction and need further diagnostic tests. This suggests that the norms of this study aid the neuropsychologist in

C. J. Long and K. Klein

344

determining whether cerebral dysfunction is present. The resulting decision should correlate highly with the outcome from more comprehensive medical tests. A second level of analysis could compare the patient’s profile with nonmedical norms and the nature and extent of cognitive weaknesses can be interpreted in this context. In summary, it is evident that more specific age norms are needed to avoid misclassification of normal functioning elderly adults, or elderly adults whose weaknesses are not attributed to significant neurological disease or damage, as brain damaged. Such norms must take into account the differential patterns of change across the various tests. Those tests most sensitive to brain damage were complex processing and visuospatial tasks found to decline the most, whereas sensory, motor, and language tasks declined the least. With regard to lateralized decline with age, it is felt that the pattern of decline on specific tests is more likely related to the increased complexity of the task and the relative difficulty elderly people have in learning new tasks, rather than reflecting a differential deterioration of the two hemispheres. REFERENCES Bak, J. S., & Greene, R. L. (1980). Change in neuropsychological function in an aging population. Journal of Consulting and Clinical Psychology, 48, 395-399. Bayley, N., & Oden, M. H. (1955). The maintenance of intellectual ability in gifted adults. Journal ofGerontology, 10, 91-107. Benton, A. L., Eslinger, P. J., & Damasio, A. R. (1981). Normative observations on neuropsychological test performances in old age. Journal of Clinical Neuropsychology, 3, 33-42. Bigler, E. D., Steinman, & Newton, J. S. (1981). Clinical assessment of cognitive deficit in neurologic disorder I: Effects of age and degenerative disease. CIinicalNeuropsychology, 3,

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on Neuropsychological

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