Regular casting in the brain

The brain organizes casting for different cells
For decades, neuroscientists have been asking how the brain can learn new tasks over and over again without ever having to grow in the course of life. There is evidence that the number of brain cells - for example, nerve cells and glial cells - initially increases as we learn, but many are later discarded or assigned to different roles. Scientists from Germany and Sweden present this theory in the journal Trends in Cognitive Sciences.

"The volume of the brain increases in the first stages of learning, and then normalizes partially or even completely," says first author Elisabeth Wenger, a neuroscientist at the Max Planck Institute for Human Development in Berlin. "It seems to be efficient, first exploring the possibilities of trying out different structures and cell types, selecting the best and then getting rid of those that are no longer needed."

The brain organizes casting. (Image: denisismagilov / fotolia.com)

She metaphorically describes brain cells as actors participating in a casting for a film directed by the brain: the brain invites various candidates to produce new cells, and this causes its macroscopically apparent volume growth. The brain then tries different functions - to see which cells are best at storing or sharing the information; these are then kept. The other candidates are then rejected or given other roles.

As an indication of such a mechanism, the scientists cite a study in which right-handed people learned to write and draw with their left hands. After a month, her brain volume had increased, but three weeks later it was almost back to normal. Researchers made similar observations in other studies, where, for example, monkeys learned to use a rake to feed or rats learned to distinguish sounds.

Phenomenon known from animal studies
Wenger and her co-authors Claudio Brozzoli, Ulman Lindenberger, and Martin Lövdén were surprised at how many times the phenomenon of brain expansion and renormalization has been identified in animal studies and believe that it applies to human brains as well. "We are definitely not the first to suggest or even discover the expansion and renormalization model," says Wenger. "But we are the ones who are bringing the model into connection with volume changes in human gray matter for the first time."

Scientists think this theory should influence the way researchers conduct brain studies. "It has now become clear that just the typical two-time study design is unsuitable for grasping the full extent of the changes taking place," notes Wenger. "This theory requires the use of study designs with a higher number of measurement times to fully represent changes in brain volume."

This work was supported by the Max Planck Society, the European Research Council, the Swedish Research Council, the European Research Institute in Florence and the Agence Nationale de la Recherche. Original work. Wenger, E., Brozzoli, C., Lindenberger, U., & Lövdén, M. (2017), Expansion and renormalization of human brain structure during skill acquisition Trends in Cognitive Sciences, 21 (12), 930-939