Birth Order Matters for Wiring Brain’s Vision Centers

In a recent study, researchers from the University of California San Diego School of Medicine found evidence suggesting that neurons in the developing brains of mice are guided by a simple but elegant birth-order rule that allows them to find and form their proper connections. The brain starts with just one neuron that increasingly divides up to 250,000 new neurons per minute at times during early development. Scientists have been trying to figure out exactly how these neurons decide which other neurons to connect to, a process neuroscientists call target selection. To better understand how a young brain gets wired, researchers focused on the development of retinal ganglion cells (RCGs) in mice, which connect the eyes and brain. During the study, scientists tagged RCGs and watched where they directed their axons during development. The study’s main find is that early RCGs — those created early in the sequence of brain division — make a lot of connections to other neurons in addition to a lot of mistakes—which they correct by repositioning or removing their axons. In contrast, later RCGs were observed to be highly accurate in their target selection skills, making almost no errors. “The neurons are paying attention to when they were born and reading out which choices they should make based on their birthdate,” said the study’s lead author. The study is among the first to show that the timing of neuronal generation is linked to how neurons achieve specific brain wiring. To read more about this study, click here.