Above: A video from Harvard Medical School describing how neural networks are studied, a summary of how they work, and why it is important.
Scientists at the University of Brussels have published detailed observations of nerve-cell growth, beginning just after differentiation. Human neurons take years to reach full maturity and connectivity to the nervous system, making it difficult to observe in humans. Scientists want to understand the complete growth cycle to develop effective treatments for neurological disorders, ranging from intellectual disability to schizophrenia.
Researchers overcame the difficulty of observing neuron development in humans by transplanting human neurons to mice. First, human stem cells were differentiated to neurons and immediately transplanted into mice. Then, a singular neuron was transplanted to one mouse so the researchers could monitor the single-cell development. The strategy shows how neurons interact and grow within a living system.
Observations revealed that the human neurons transplanted into mouse brains developed normally. Instead of developing in a few weeks like mouse neurons, the transplanted neurons took months to reach full maturity. This suggests that human neurons grow based on internal timing signals. Additionally, once the implanted neurons matured, they were fully functional in the mouse's brain circuit. When the mice were subjected to a vision test, the implanted human neuron was not only active in processing information but acted with a higher degree of precision.
The long maturation of human neurons is what gives the human brain, and the mysterious brian cortex, cognitive abilities that no other living organism has. Scientists are using techniques, that are only possible with recent technological advances, to understand how the brain should work. The hope is to use these observations to inform treatment for neurological disorders.