Cognitive reserve modulates functional brain responses during memory tasks: a PET study in healthy young and elderly subjects.

Cognitive reserve (CR) is the ability of an individual to cope with advancing brain pathology so that he remains free of symptomatology. Epidemiological evidence and in vivo neurometabolic data suggest that CR may be mediated through education or IQ. The goal of this study was to investigate CR-mediated differential brain activation in 17 healthy young adults and 19 healthy elders. Using nonquantitative H(2)(15)O PET scanning, we assessed relative regional cerebral blood flow while subjects performed a serial recognition memory task under two conditions: nonmemory control (NMC), in which one shape was presented in each study trial; and titrated demand (TD), in which study list length was adjusted so that each subject recognized shapes at approximately 75% accuracy. A factor score that summarized years of education and scores on two IQ indices was used as an index of CR. Voxel-wise, multiple regression analyses were performed with TD minus NMC difference PET counts as the dependent variable and the CR variable as the independent variable of interest. We identified brain regions where regression slopes were different from zero in each separate group, and also those where regression slopes differed between the two age groups. The slopes were significantly more positive in the young in the right inferior temporal gyrus, right postcentral gyrus, and cingulate, while the elderly had a significantly more positive slope in left cuneus. Brain regions where systematic relationships between CR and brain activation differ as a function of aging are loci where compensation for aging has occurred. They may mediate differential ability to cope with brain changes in aging.