PATTERNS OF COGNITIVE DECLINE IN AGED RHESUS-MONKEYS

Although cognitive decline has been well established as a consequence of aging in non-human primate models, the prevalence or frequency of i mpairment for specific age ranges has not been described. The first ai m of this study was to estimate prevalence of cognitive impairment on each of the six tests of cognitive performance by comparing the perfor mance of early-aged (19-23 years old), advanced-aged (24-28 yeras old) , and oldest-aged (29 + years old) monkeys to that of young adults ( < 15 years old). The second aim was to derive a single overall measure of cognitive performance to help classify behavioral function in our a ged monkeys. Accordingly, we obtained performance measures for these a ge groups on six behavioral measures: (1) acquisition of the delayed n on-matching-to-sample task (DNMS); (2) performance of the DNMS with a delay of 120 sec; (3) the spatial condition of the delayed recognition span test (DRST); (4) the color condition of the DRST; (5) spatial re versal learning; and (6) object reversal learning. Early-aged monkeys displayed prevalence rates of impairment significantly greater than ze ro on all tasks except the DRST-color. The highest prevalence of impai rment was observed in this age group in a task measuring spatial memor y (DRST). Significant trends toward progressively higher impairment ra tes in advanced-aged and oldest-aged monkeys were observed for DNMS-ac quisition, DRST-color and spatial reversal learning tasks. A linear tr ansformation of standardized scores on the six cognitive tests was der ived by means of principal components analysis (PCA). The first PCA (P CA1) included data from 30 monkeys with available data on all six meas ures, and yielded a composite measure which declined linearly with inc reasing age (r = -0.74). A second PCA (PCA2) was performed on data fro m 53 monkeys for which three test scores (DNMS-acquisition, DNMS-120s delay, and DRST-spatial condition) were available. The composite score derived from this analysis was highly correlated (r = 0.93) with the composite score from PCA1, suggesting that a score based on only three tests may provide an adequate classification of global cognitive abil ity. (C) 1997 Elsevier Science B.V.