Researchers from the University of Tokyo studied how the brain works based on the connections made between multiple regions in the brain by creating a working model of a cerebral tract in the lab.
Different areas of neurons divide the cortext and each area has its own unique role that could be control for vision, movement, speech, and others. The cerebral tracts serve as channels where these cortical areas communicate. Axons form these cerebral tracts. This research created a method where nerve tissues imitate cerebral tracts and which aimed to determine the time connections are made in the brain. Moreover, its target was to find out how independent cognitive tasks are integrated by these tracts into a unified intelligence.
Yoshiho Ikeuchi, lead author of the team, with his colleagues used human induced pluripotent stem cells (iPCSs) to grow spheroids of neurons that imitate the cerebral cortex. A microdevice were attached with two spheroids of neurons at both of its ends. When this is done, the spheroids extend axons toward each other.
"After 25 days, both tendrils of axons reached all the way down the channel, and the two cortical spheroids were connected," says Ikeuchi. "We know this was a functional electrical connection, because if one spheroid was electrically stimulated, the other would respond after a short delay. This resembles the situation in a real brain, where distant regions communicate during cognition."
The complexity of the development of the brain can be seen as the cerebral tracts only responded during the right conditions. The two ends of the microdevice must have the right attachments. Axons still extended from the neurons at the other end, but not as significant. If a glass bead is placed at the empty end, the fascicle didt not grow.
"The spheroids promoting each other to grow fascicles is very interesting," says Takaaki Kirihara, first author of the study in iScience. "It implies that opposing axons mutually guide each other, connecting two groups of neurons. This could help explain how reciprocal connections are formed between distant regions of the brain, sometimes even between different hemispheres."
The model created might not be the same as the living brain. However, the model is realistic. The formation of cerebral tract needs the gene L1CAM. Most of the axons did not cluster into a bundle when the L1CAM was suppressed in the spheroids. This implies that the model is not only meant for modelling a normal brain tissue, but also cerebral tract disoreders of the brain.
