The Neurobiology Behind Individuality

When a group of genetically identical mice lived together in the same complex for three months, mice that explored their surroundings more broadly grew more new neurons than those who were less adventurous, according to a study published May 9, 2013 in Science Magazine. This link between inquiring behaviors and the adult growth and development of nervous tissue shows that brain plasticity can be shaped by experience and suggests that this may promote individuality, even in genetically identical organisms.
Scientists have long tired to tackle the question of how individual differences in behavior and personality develop in terms of the way genes and the individual's surroundings interact. "But there is next to nothing [known] about the neurobiological mechanisms underlying individuality" says Gerd Kempermann of the German Center for Neurodegenerative Diseases in Dresden.
A logical way to study this would be to look at how the brain's structure and function change over time (the brain's plasticity). This plasticity is hard to study, though, because it takes place mostly at the synaptic level, so Kempermann and his colleagues decided to look at the growth of new neurons in the adult hippocampus, which can be found easily. Earlier studies have shown that activity increases the adult growth an development of nervous tissue in groups of genetically identical mice, but there were differences between individuals in the amount of neuron growth.
To find out why, Kempermann and his colleagues housed 40 genetically identical female inbred mice in a 5-square meter, 5-level enclosure filled with different sorts of objects made to encourage activity and exploration. The mice were tagged with radio-frequency-infer-red transponders and had 20 antennas in the complex that caught their every movement. After 3 months, the researchers assessed the growth and development of nervous tissue in the mice by counting their fast-multiplying precursor cells, which had been numbered before the study began.
The researchers saw that individual differences in exploratory behavior corresponded with individual differences in the numbers of new neurons generated. "To our knowledge, it's the first example of a direct link between individual behavior and individual brain plasticity," said Kempermann.
However, be cautious about putting all the differences on their surroundings. Even though the mice in the study were genetically the same, they were not behaviorally identical to begin with. It is clear that some variation happens at an extremely early stage, making the mice more or less likely to explore.
These findings could help explain why human identical twins raised in the environment end up with different personalities. Photo Credit