A Field Trip to Plasticity

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Science Translational Medicine  29 May 2013:
Vol. 5, Issue 187, pp. 187ec90
DOI: 10.1126/scitranslmed.3006580

Our treasured individuality relies on the brain’s powerful capacity to adapt to environmental changes within limits imposed by an individual genetic blueprint. Even in the case of monozygotic twins who were reared together, the impact of the poorly defined “nonshared environment” results in visible behavioral differences. Now, Freund et al. show that, like monozygous twins, genetically identical mice can also develop unique personalities.

The authors found that experience-based individuality in mice depended on active field exploration. Genetically identical mice that were allowed to wander freely through an enriched environment for 3 months displayed a significant increase in de novo hippocampal neurogenesis as compared with that of control mice. The latter process feeds the brain with freshly generated neurons that become integrated into neuronal networks and thereby increase brain plasticity—the organ’s ability to change as a result of experience. In a set of elegant experiments, Freund et al. showed a direct correlation between the broadness of exploration and the amount of neurogenesis in individual mice. This finding suggests that individual environmental experiences shape hippocampal connections according to individual needs and thereby ensure environmental adaptability over the mouse’s lifetime. Similar to the human twin studies, unfettered roaming in rich environments spurred the emergence of “behavioral individuality” (defined by the diversity of spatial exploration) and a mouse-specific “life space” (the area of an identical environment occupied most frequently by an individual mouse).

Future studies are needed to define the molecular mechanisms that enable mice to translate life experiences into biological processes that contribute to hippocampal neurogenesis and brain plasticity. It is exciting to envision the existence of experience-induced ligands that, once identified, may help humans to maximize brain adaptation to the ever-increasing flow of information.

J. Freund et al., Emergence of individuality in genetically identical mice. Science 340, 756–759 (2013). [Abstract]

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