Text

theses

Among humans, estimates of the heritability of intelligence are high, although there is also evidence that this trait is quite malleable. However, little is known about the genotypes and environmental states that are relevant to intelligence, much less how they react together. This is in part due to limitations on work with humans, which are largely confined to assessing heritability and malleability using only correlational methods. In the past, our group has developed a battery of cognitive tasks in mice where the performance of individuals is correlated across all tests. Aggregate performance on this battery of tests predicts individuals’ performance on other cognitive abilities implicated in human general intelligence such as reasoning and working memory. Thus it has been asserted that the “general cognitive ability” (GCA) scores obtained in this battery are analogous to human IQ scores. Here we attempted to answer a critical question: How much the individual differences in mouse intelligence can be influenced by genetics and the environment? To make these determinations, we used a strategy analogous to classic human twin/adoption studies. Unlike human studies, in the present case, different environments were under experimental control and thus could be administered differently to different members of sibling cohorts. We used 232 outbred male mice consisting of 58 families of 4 full siblings (fraternal twins) and provided different environments to the siblings from each family (analogous to “twins raised apart”). For the environmental manipulation, half of the sibling groups stayed in a standard colony room with little stimulation, while the other half of the siblings were exposed to environments that are prone to influence cognitive development: physical exercise and daily exposure to novel experiences. Similar to our previous work, here GCA (i.e., intelligence) accounted for 19.5% of the common variance in mice’s performance from an exploratory factor analysis. We found that GCA was moderately malleable, with environmental enrichment increasing GCA scores by 0.44 standard deviations. In humans, this increase would represent an increase of 6.6 IQ points. Although here we used a combination of environmental factors that were likely to be effective, these were admittedly limited in scope and strength, and so GCA can potentially be more malleable than these results suggest. The population of all mice combined showed a GCA heritability of 0.24, quite comparable to values estimated by others in rodents and non-human primates. To our surprise, our Enrichment group had a heritability not significantly different from zero, while our Control group had a moderate heritability of 0.55. This is the opposite of what is typically found in humans, where heritability is higher in populations drawn from higher SES environments. Also, unexpectedly, we did not find evidence for G×E in our study. The results from the current study could help laying the groundwork for future studies on the independent effects and interactions between environment and genes in shaping general intelligence in humans.

ETD_8610

Ph.D.

Includes bibliographical references

by Bruno Sauce Silva

doi:10.7282/T3F47SB5

ETD doctoral

The author owns the copyright to this work.