New brain atlas reveals how the human neocortex forms over time

In a bid to better understand, and potentially treat, a host of conditions that affect early cognition, neurodevelopment and the brain later in life, investigators at Johns Hopkins Medicine and colleagues throughout the world have been mapping the molecular construction of the human brain. These models, which are supported in part by federal and international research grants, are helping researchers study genetic links and pathways involved in a variety of conditions, ranging from autism spectrum disorder, which affects about 1 in 31, or 3%, of children in the U.S., to Alzheimer's disease, which is estimated to affect more than 7 million U.S. adults, including 1 in 9, or 11%, age 65 and older.

To support this blueprint, Carlo Colantuoni, Ph.D., an adjunct professor of neurology at Johns Hopkins Medicine and the Institute for Genome Sciences at the University of Maryland School of Medicine, and other researchers have, in their most recent study, brought together data from nearly 200 published studies and more than 30 million cells to advance insight about how the neocortex, the outermost layers of the brain, develops and forms over time. This region of the brain is responsible for a variety of functions, including how we think, sense, process and store information, and make decisions.

"Our goal is to understand how the neocortex is built on a cellular level, and identify clues to the earliest stages of developmental delays and brain disorders," said Colantuoni. "By mapping the cell transitions and genes that give rise to the intricate structure and function of the neocortex, we can better understand, and then attempt to treat, disorders that arise in the womb, during infancy and childhood, and even much later in life."

Not only does this enhanced atlas help researchers study genetic links for autism spectrum disorder, it can also provide insight into rare conditions like microcephaly, which can begin before birth and drastically affect the growth of the brain. A strength of bringing this information together, which is now available through Nature and Nature Neuroscience, is that researchers can study granular stages of development to identify typical growth patterns and then pinpoint the origins and pathways of neurodevelopmental delays and disease.

In addition to mapping a human model of the neocortex, the authors published a mammal and mouse model. These different atlases show that gene expression programs that began as diffuse networks millions of years ago were more recently focused in human neural stem cells to drive expansion of the human neocortex. This process, the researchers say, helped contribute to and, in part, explains differences in higher human cognitive abilities compared with other animals.

Using the accumulated data, the researchers also charted the maturation of neurons in the human neocortex, a process that has become longer over evolutionary time as the human neocortex and mental capacity have expanded. For example, this type of neural development takes weeks in a mouse but many years in humans. This represents differences in advanced systems that enable the human brain to adapt and learn how to interpret complex social, environmental and sensory inputs over an extended developmental period.

These resources are now available as an open-access web portal to empower other researchers investigating human brain development and disease. Collectively, says Colantuoni, these and other brain-charting efforts aim to help researchers study mechanisms of brain disease throughout the lifespan and provide a tool to better support and accelerate everyday research.

Researchers without coding expertise can explore the expression patterns of individual genes of interest, chart the coordinated expression of gene modules that work together in specific ways during development, and contribute their own data to expand the resource.