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Why Individuals Are Not Alike

Neurobiologists studied how brain development influences behavioral differences

№ 051/2020 from Mar 06, 2020

Neurobiologists at Freie Universität Berlin led by Prof. Dr. Bassem Hassan, Einstein BIH Visiting Fellow, in collaboration with the group led by Prof. Dr Robin Hiesinger at the Department of Biology, Chemistry, and Pharmacy at Freie Universität Berlin, described in a study published in Science why fruit flies display individual behavioral differences despite having the same genotype and being reared in identical environmental conditions. This work was done in collaboration with the University of Freiburg, VIB KU Leuven Campus, and ICM Paris. The team at the Division of Neurobiology, Freie Universität Berlin was funded by the Einstein Foundation. The study showed that individual flies react very differently to an identical visual stimulus. The authors found that these individual differences in behavior were stable for weeks and were independent of genetic variability and environmental factors. They concluded that developmental noise lead to different wiring of certain nerve cells in the vision-processing part of the fly’s brain and that these individual differences in brain wiring influence the behavior of the fly.

The researchers determined from key experiments that the asymmetry of nerve connections between the right and left brain is an important factor that leads to differences in behavior. Accordingly, fruit flies with symmetrical nerve cell connections head more indirectly towards objects than animals with asymmetrical brains. The authors assume that this additional variability factor enables animals to develop heading differences even with the same or similar genetics, thereby increasing the likelihood of survival of the population.

Why every person and every animal differs in behavior from its peers is one of the central questions of neurobiology and psychology. The answer to this question is often given as an interplay of genetic differences and environmental factors. Many studies have shown the importance of both factors. To illustrate this: genetics and environmental factors can be comprehensively used to explain the similarities in behavior of identical twins. They are genetically identical and grow up in most cases under very similar environmental conditions. However, both factors are much less suitable to explain the differences in behavior of identical twins. A third factor, the influence of developmental noise is in that context much better suited to explain the differences.

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