Serotonin, or the happiness neurotransmitter, has a crucial role to play in brain development – researchers have found that it acts as a growth factor for basal progenitors in part of the developing human, but not mouse, brain. Known as the “neocortex,” this region enables more complicated processes in humans such as speaking, dreaming and thinking.

Researchers at the Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG), and colleagues at the University Hospital Carl Gustav Carus in Dresden, Germany, hope their findings may help explain how malfunctions of serotonin – and its receptor – during brain development can lead to congenital disorders including Down syndrome and autism, and how to treat them.

“I exploited datasets generated by [MPI-CBG] and found that the serotonin receptor HTR2A was expressed in foetal human, but not embryonic mouse, neocortex. Serotonin needs to bind to this receptor in order to activate downstream signaling between nerve cells that contribute to well-being,”said postdoctoral researcher Lei Xing.

“I asked myself if this receptor could be one of the keys to the question of why humans have a bigger brain.”

When the researchers induced the production of the HTR2A receptor in embryonic mouse neocortex, they noticed that the now-active serotonin caused the production of more basal progenitors in the animals’ developing brain. “More basal progenitors can increase the production of cortical neurons, which paves the way to a bigger brain,” offered Lei Xing.