Cognitive performance across the life course of Bolivian forager-farmers with limited schooling

Abstract

Cognitive performance is characterized by at least two distinct life course trajectories. Many cognitive abilities (e.g., "effortful processing" abilities, including fluid reasoning and processing speed) improve throughout early adolescence and start declining in early adulthood, whereas other abilities (e.g., "crystallized" abilities like vocabulary breadth) improve throughout adult life, remaining robust even at late ages. Although schooling may impact performance and cognitive "reserve," it has been argued that these age patterns of cognitive performance are human universals. Here we examine age patterns of cognitive performance among Tsimane forager-horticulturalists of Bolivia and test whether schooling is related to differences in cognitive performance over the life course to assess models of active versus passive cognitive reserve. We used a battery of eight tasks to assess a range of latent cognitive traits reflecting attention, processing speed, verbal declarative memory, and semantic fluency (n = 919 individuals, 49.9% female). Tsimane cognitive abilities show similar age-related differences as observed in industrialized populations: higher throughout adolescence and only slightly lower in later adulthood for semantic fluency but substantially lower performance beginning in early adulthood for all other abilities. Schooling is associated with greater cognitive abilities at all ages controlling for sex but has no attenuating effect on cognitive performance in late adulthood, consistent with models of passive cognitive reserve. We interpret the minimal attenuation of semantic fluency late in life in light of evolutionary theories of postreproductive life span, which emphasize indirect fitness contributions of older adults through the transfer of information, labor, and food to descendant kin. (PsycINFO Database Record

Figure 1

Smoothed curve of the effect of age on cognitive performance, controlling for sex, education and Spanish fluency, based on GAM (see text). Upper and lower lines of each curve represent 95% confidence intervals. Rug marks on the X-axis indicate the range of unique ages in the sample (range: 8–88 yrs). In all models, age represented a significant smoothing term (p’s < 0.001). Sex, education, and Spanish fluency added as controls to the models.

Figure 2

Estimated age of peak cognitive performance for all tasks. (a) composite “effortful processing” components, (b) category fluency subtasks, and (c) composite scores. Rug marks on the X-axis represent the range of unique ages in the sample.

Figure 3

Segmented linear regression predicting cognitive performance across two levels of educational attainment (<2 years vs. 2+ years).

Figure 4

“Effortful processing” cognitive performance, schooling and village history of schooling (only “low”, “high” shown here). Based on Model 3 in Table 8.