Dresden/Berlin, 10 May 2013 - How do living beings become individuals that differ from others in terms of their very personal brain structure and behaviour? Researchers in Dresden, Berlin, Münster and Saarbücken have now taken a decisive step towards answering this question: They were able to prove in mice that experiences can influence the formation of new brain cells and thus lead to measurable changes in the brain. The results of the study will be published in the journal Science on 10 May. The DFG Research Centre for Regenerative Therapies Dresden - Cluster of Excellence at TU Dresden (CRTD), the Dresden site of the German Centre for Neurodegenerative Diseases (DZNE) and the Max Planck Institute for Human Development in Berlin were in charge of the study.
The brain literally grows with its tasks. It changes throughout our lives with every new experience, which means that our personality and behaviour also continue to develop. But what exactly is the connection between individual experience and the brain structure of each individual? Why are identical twins sometimes so different, even if they grow up together? To investigate these questions, the researchers observed 40 genetically identical mice. They shared an enclosure with a wide range of activities and exploration opportunities.
"Not only did the animals all have the same genetic material, they were also all exposed to the same environmental conditions," says study leader Gerd Kempermann, Professor of Genomics of Regeneration at the CRTD and site spokesperson for the DZNE in Dresden, describing the experimental setup. "At the same time, the enclosure was so varied that each mouse had its own individual experiences in this environment. As a result, the animals differed more and more in their experiences and behaviour over time."
New nerve cells for individual brains
All the mice were fitted with special microchips that triggered radio signals. This enabled researchers to create movement profiles and quantify the activity of the animals. Conclusion: Despite a common environment and identical genetic material, the mice showed very individual behavioural patterns. They reacted differently to their environment. Over the course of the three-month experiment, these differences became increasingly clear.
"The animals developed different levels of activity in their shared environment. This correlated with the formation of new nerve cells in the hippocampus region of the brain responsible for learning and memory," says Kempermann. "Animals that explored the enclosure particularly actively also had more new nerve cells than animals that behaved comparatively passively.
Adult neurogenesis, as the formation of nerve cells in the hippocampus is called, enables the brain to react flexibly to new information. With the current study, the scientists have now demonstrated for the first time that personal experiences and the resulting behaviours contribute to the "individualisation of the brain". This individualisation can be attributed neither to the environment nor to genetic differences.
"Adult neurogenesis also occurs in the human hippocampus," says Kempermann. "We therefore suspect that we have discovered a neurobiological basis of individuality that is also valid for humans."
Impulses for interdisciplinary discussions
"The empirical evidence that behaviour and experience contribute to differences between individuals is important for debates in psychology, education, biology and medicine," says Professor Ulman Lindenberger, Director of the Developmental Psychology Research Unit at the Max Planck Institute for Human Development (MPIB) in Berlin. This involves, for example, the question of how behaviour influences cognitive performance in old age. "Our results show that development itself contributes to differences in behaviour. This was already suspected, but now there is neurobiological proof of this for the first time."
The study also examined the animals in a control group that lived in a comparatively unattractive environment: on average, these mice produced significantly fewer new brain cells than the animals in the experimental group. "From the perspective of educational research, our experiments show that a rich environment promotes the formation of new brain cells and thus the development of individuality," comments Ulman Lindenberger on the results.
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Source: Press release of the CRTD, DZNE, MPI for Human Development from 10.5.13
