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The Neurobiology of Individuality

Mice that explore more have higher levels of neurogenesis, suggesting a link between experience, brain plasticity, and the emergence of distinct personalities.

By | May 9, 2013

WIKIMEDIA, RAMAWhen a group of genetically identical mice lived in the same complex enclosure for 3 months, individuals that explored the environment more broadly grew more new neurons than less adventurous mice, according to a study published today (May 9) in Science. This link between exploratory behavior and adult neurogenesis shows that brain plasticity can be shaped by experience and suggests that the process may promote individuality, even among genetically identical organisms.

“This is a clear and quantitative demonstration that individual differences in behavior can be reflected in individual differences in brain plasticity,” said Fred Gage of the Salk Institute for Biological Studies in La Jolla, California, who was not involved the study. “I don’t know of another clear example of that . . . and it tells me that there is a tighter relationship between [individual] experiences and neurogenesis than we had previously thought.”

Scientists have often tried to tackle the question of how individual differences in behavior and personality develop in terms of the interactions between genes and environment. “But there is next to nothing [known] about the neurobiological mechanisms underlying individuality,” said Gerd Kempermann of the German Center for Neurodegenerative Diseases in Dresden.

One logical way to study this phenomenon is to look at brain plasticity, or how the brain’s structure and function change over time. Plasticity is hard to study, however, because it mostly takes place at the synaptic level, so Kempermann and his colleagues decided to look at the growth of new neurons in the adult hippocampus, which can easily be quantified. Earlier studies have demonstrated that activity—both physical and cognitive—increases adult neurogenesis in groups of genetically identical mice, but there were differences between individuals in the amount of neuron growth.

To understand why, Kempermann and his colleagues housed 40 genetically identical female inbred mice in a complex 5-square-meter, 5-level enclosure filled with all kinds of objects designed to encourage activity and exploration. The mice were tagged with radio-frequency infer-red (RFIR) transponders, and 20 antennas placed around the enclosure tracked their every movement. After 3 months, the researchers assessed adult neurogenesis in the mice by counting proliferating precursor cells, which had been labeled before the study began.

The researchers found that individual differences in exploratory behavior correlated with individual differences in the numbers of new neurons generated. “To out knowledge, it’s the first example of a direct link between individual behavior and individual brain plasticity,” Kempermann said.

Gage cautions about pinning all the differences on the environment, however. Although the mice in the study were genetically identical, he said, they were not behaviorally identical to begin with: clearly some variation occurs at a very early stage that makes them more or less prone to explore. “It’s incorrect to think of it that the environment caused the difference between the mice,” he said. “The difference was already there, and the environment amplified that difference. My own personal bias is that there are likely genetic events that happened at germline, or somatic events over time,” that set the stage for these subtle behavioral differences that are subsequently amplified.

The findings could help explain why human identical twins raised in the same family end up with different personalities. “These kinds of processes are notoriously difficult to study in people, because we can’t control human environments experimentally,” said Eric Turkheimer, a psychologist at the University of Virginia, who studies how differences in the personalities of identical twins emerge over time. “That’s why an animal model is so important.”

Indeed, the research provides a novel approach to studying the role of the environment in shaping personalities. “This idea of having Infrared implants in the animals and watching them form patterns of behavior over time in this wonderfully complex 3D maze is a really useful tool,” said Gage. “I think it will be very helpful for those of us interested in individual differences [in brain plasticity],” and could be used to explore the genomic basis of the initial behavioral differences between the mice.

“We’ve come up with an animal model to help address the ways living our lives make us who we are,” said Kempermann. “So we have touched on an approach that allows us start to get the small part of an answer to a very big question.”

J. Freund et al., “Emergence of individuality in genetically identical mice,” Science, 340:756-59, 2013.

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Avatar of: TGrant

TGrant

Posts: 1

May 13, 2013

I wonder if you have considered doing research in a classical Montessori classroom (AMI affilitated)?

"The material of our schools today is based on the selection that the children have voluntary made themselves from the mass of things that was placed at their disposal…  This selection brought us to the conception that there must be just that amount and no more. . . . The fundamental fact in the preparation of the environment is to have only one set of each type of material." ~Dr. Montessori.

In other words, children in Montessori schools would all have access to the same educational materials, and lessons are given in similarly "prescribed" ways. Yet, the goal is to support the emergence of diverse and fully functional individuality. 

Dr. Angelinie Stoll Lillard's most recent research studied the "fidelity" of Montessori programs in relationship to outcomes (finding that the more schools modified Montessori pedegogy with supplementary materials, the more they lowered student outcomes). Classical Montessori schools (usually AMI affiliated) remain consistent with established pedagogical principles --and use only the autodidactic materials developed by Dr. Montessori (and their use showed significant advantage over other methods of education).

It seems like a constant environment that could be used to test your hypothesis (without requiring any more of children than they are already experiencing).

Avatar of: LeeH

LeeH

Posts: 29

May 13, 2013

I believe this merely recapitulates what we already know...a stimulating environment provides intellectual growth.  This fundamental fact goes back to Skinner and others.  Now it's linking it to the underlying neurology that provides the physical explanation and, potentially, ways in which one can "stimulate" further.

Avatar of: James V. Kohl

James V. Kohl

Posts: 110

May 13, 2013

These facts do not go back to Skinner, but they do extend well to what is currently known about classically conditioned behavior associated with innate differences in learning and memory.

1. Adaptive evolution of individuality in mammals occurs via ecological, social, neurogenic, and socio-cognitive niche construction.

2. Experience-dependent epigenetically-effected olfactory receptor gene choice is reciprocally determined by nutrient-dependent pheromone-controlled reproduction in species from microbes to man.

3. Facts number 1 and 2 link genetically predisposed 'conditions of life' (e.g., the requirements for food and for reproduction) to Darwinian theory via natural selection for food. The metabolism of nutrients to pheromones enables organisms to selectly reproduce via variations in their response to signals of individual and colony-wide reproductive fitness.

The conserved molecular mechanisms of my model, in which olfaction and odor receptors provide a clear evolutionary trail that can be followed from unicellular organisms to insects to humans, have been detailed across all species. Excellent model organisms of single amino acid substitutions are widely distibuted.

My choice was the honeybee model organism of nutrient-dependent pheromone-controlled adaptive evolution as it also seems to exemplify an intermediate level of experience-dependent hormone-organized and hormone-activated 'embodied cognition'. See for example in mice: The activity-dependent histone variant H2BE modulates the life span of olfactory neurons.

For our 1996 Hormones and Behavior review that incorporated what was then known about molecular epigenetics into a mammalian model of hormone-organized and hormone-activated behavior see: From Fertilization to Adult Sexual Behavior.

Avatar of: Ed M.

Ed M.

Posts: 44

May 13, 2013

So cultures that explored the world instead of staying home would engender  more complex, more  plastic brains.

Which would explain the scientific ascendancy of the Mediterranean world and then Europe.  Map-making, star-charts, geometry, the clock, et al. come as a result of "exploring the environment".

China had the compass first but not the urge to explore (aside from one fleet that was ultimately recalled and its discoveries never followed up on), and remained insular and backward compared to the West- until Europeans sailors finally showed up shook them out of their complacency.

Use it or lose it has a neurological basis.

 

Avatar of: Neurona

Neurona

Posts: 29

May 30, 2013

More exploration = more physical exercise. Did they control for that? Because I thought Gage had shown some time ago that exercise alone enhances neurogenesis.

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