Impairment in Working Memory and Executive Function Associated with Mercury Exposure in Indigenous Populations in Upper Amazonian Peru.

The Matsigenka people living traditional lifestyles in remote areas of the Amazon rely on a fish-based diet that exposes them to methylmercury (MeHg) at levels that have been associated with decreased IQ scores. In this study, the association between Hg levels and working memory was explored using the framework of the Multicomponent Model. Working memory tasks were modified to fit the culture and language of the Matsigenka when needed and included measures for verbal storage (Word Span) visuospatial storage (Corsi Block Task) and a measure of executive functions, the Self-Ordered Pointing Task (SOPT). An innovation of the Trail Making Tests A & B (TMT A & B) was pilot tested as another potential measure of executive functions. The mean hair Hg levels of 30 participants, ages 12 to 55 years, from three different communities (Maizal, Cacaotal and Yomibato) was 7.0 ppm (sd = 2.40), well above the World Health Organization (WHO) limit for hair of 2.0 ppm and ranged from 1.8 to 14.2 ppm, with 98% of a broader sample of 152 individuals exceeding the WHO limit. Hair Hg levels showed significant associations with cognitive performance, but the degree varied in magnitude according to the type of task. Hg levels were negatively associated with executive functioning performance (SOPT errors), while Hg levels and years of education predicted visuospatial performance (Corsi Block accuracy). Education was the only predictor of Word Span accuracy. The results show that Hg exposure is negatively associated with working memory performance when there is an increased reliance on executive functioning. Based on our findings and the review of the experimental research, we suggest that the SOPT and the Corsi Block have the potential to be alternatives to general intelligence tests when studying remote groups with extensive cultural differences.

Training monitoring skills improves older adults' self-paced associative learning.

We investigated a memory-enhancement program that involved teaching older adults to regulate study through self-testing. A regulation group was taught standard strategies along with self-testing techniques for identifying less well-learned items that could benefit from extra study. This group was compared with a strategy-control group, which was taught only strategies, and with a waiting-list control group. Greater training gains were shown for the regulation group (effect size, d = 0.72) than for the strategy-control (d = 0.28) and waiting-list control (d = 0.03) groups, indicating that training a monitoring skill--self-testing--can improve older adults' learning.

Effects of aging on the magnitude and accuracy of quality-of-encoding judgments.

Age invariance in monitoring associative learning has been the norm in numerous investigations concerning how accurately people predict future recall, predictions that are based partly on people's beliefs about forgetting. In this study, we obtained a measure of monitoring that is minimally influenced by beliefs about forgetting. Participants made quality-of-encoding (QUE) judgments by rating how well each item had been encoded. In 2 experiments, older and younger adults studied 60 paired-associate items; immediately after studying each one, they made a QUE judgment. Each item was presented at a 4-s or 8-s presentation rate. QUEs from both age groups were sensitive to the production of different strategies, presentation rate, and item characteristics. Reliable age differences in the correlation of QUEs and subsequent recall were found for related items but not for unrelated items. The outcomes indicate similar processes for generating QUE judgments by older and younger adults, but they also suggest the possibility of an age-related deficit in the accuracy of monitoring encoding in some experimental conditions.

Patterns of impaired verbal, spatial, and object working memory after thalamic lesions.

Working memory processes in six individuals with isolated thalamic lesions were assessed. Participants were given a verbal, spatial, and object n-back task, each at three levels of task load (1-back, 2-back, and 3-back). Relative to a control group, the patients were impaired on the verbal and spatial n-back tasks, and possibly on the object n-back task as well. None of the patients showed impaired short-term memory as measured by digit span. Group differences on trials measuring matching, sequencing, and inhibitory abilities were consistent with other reports suggesting that thalamic lesions may impair the operation of executive processes.