The heterogeneity of mental aging is due to the influences of both genetic and environmental factors. Among the latter, an important role is played by intellectual activity. An association was found between the serotonin transporter 5-HTTLPR gene and the efficiency of solving cognitive tasks, and the “adaptive” nature of one of its genotypes provided grounds for studying the associations of this polymorphism with age-related changes in cognitive functions in relation to the intellectual aspect of professional work. The study included young and old scientists (scientific activity, SA, N = 132) and people with no involvement in scientific activity (NSA, N = 157). The efficiency of verbal memory was assessed in terms of reproduction of words from the right and left ears in a dichotic test procedure and recognition of previously presented words; that of imaginal memory was assessed in terms of the recognition of figures. Independently of age, SA subjects had higher measures of verbal memory than NSA. The intellectual aspect of SA was a factor preventing age-related decline in memory for words addressed to the left hemisphere. Independently of other factors, carriers of the S′ (S or LG) alleles of the 5-HTTLPR polymorphism, as compared with carriers of the L′/L′ (LA/La) genotype, demonstrated better measures of imaginal memory. Thus, the initial cognitive potential and cognitive function-stimulating aspect of SA promotes maintenance of the functional activity of the left hemisphere. Measures of right-hemisphere imaginal memory were associated with the genome.