Have you ever wondered how the social experiences you had early in life affected the way your brain developed?  How was your cerebral architecture influenced by the games of ‘peek-a-boo’ your parents played with you as a toddler or the exciting games of hide-and-seek you played with the neighborhood kids?  How would we be different if we were deprived of these experiences due to parental neglect or social isolation?  Is it possible that early life experiences shaped the way we perceive the world in adulthood, as well as determined our capacity to learn and remember?  And if so, what are the physical substrates for these processes?

In the quest to understand the interplay between social experience and brain development, scientists have successfully applied a reductionist approach to unravel important details.  Makinodan et al. published a remarkable set of experiments in the September issue of Science showing how the pattern of myelination in the prefrontal cortex of mice is sensitive to the social environment of the mouse during a temporally restricted “critical period” (postnatal days 21 to 35, which is comparable to childhood and adolescence in humans).  The experimenters compared the medial prefrontal cortices of mice that spent two-week intervals in the following three social contexts: an isolated environment (single mouse per standard cage), a regular environment (four mice per standard cage), and an enriched environment (a larger cage with eight mice and novel objects).  This brain region has been shown to be important in regulating social interaction, impulse control, planning, executive function, and decision making in humans.  It’s also one of the last regions of the brain to completely develop; it doesn’t fully mature until the early twenties.

The researchers found that the morphology of the myelin-producing cells (oligodendrocytes) in the prefrontal cortex varied drastically depending on the social environment of the mouse.  More specifically, mice that spent the duration of the critical period in isolation had thinner myelin sheaths and simpler oligodendrocyte branching patterns than mice raised in either of the other two environments.  Importantly, this effect was not observed if mice were housed in isolation after, but not during, the critical period (after postnatal day 35).  This study went on to show that when mice are deprived of social interaction during this critical period, they display deficits in working memory and social interaction tasks in adulthood, regardless of the social environment they experience as adults.

It is amazing to see how the social environment of an adolescent organism can have such drastic effects on the structure and function of the adult brain.  The fact that the physical architecture of the brain is malleable to social experience is intriguing, to say the least!  It is cool to think that the vestiges of our childhood adventures are not limited to photographs and mental imagery, but that a footprint of the experiences we shared with our friends has been left in our brain’s physical make up.

Makinodan M., Rosen K.M., Ito S. & Corfas G. (2012). A Critical Period for Social Experience-Dependent Oligodendrocyte Maturation and Myelination, Science, 337 (6100) 1357-1360. DOI: 10.1126/science.1220845
Images adapted from CorbisWikimedia Commons, and KidStock/Blend Images/Corbis
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