The human brain develops with an exquisitely timed choreography marked by distinct patterns of gene activity at different stages from the womb to adulthood, report Yale researchers. The Yale team conducted a large-scale analysis of gene activity in cerebral neocortex —an area of the brain governing perception, behavior, and cognition — at different stages of development.
“The neighborhoods get built quickly and then everything slows down and the neocortex focuses solely on developing connections, almost like an electrical grid,” said Nenad Sestan, professor of neurobiology at Yale’s Kavli Institute for Neuroscience and senior author of the study. . “Later when these regions are synchronized, the neighborhoods begin to take on distinct functional identities like Little Italy or Chinatown.”
The analysis shows the general architecture of brain regions is largely formed in the first six months after conception by a burst of genetic activity, which is distinct for specific regions of the neocortex. This rush is followed by a sort of intermission beginning in the third trimester of pregnancy. During this period, most genes that are active in specific brain regions are quieted — except for genes that spur connections between all neocortex regions. Then in late childhood and early adolescence, the genetic orchestra begins again and helps subtly shape neocortex regions that progressively perform more specialized tasks, a process that continues into adulthood.
The analysis is the first to show this “hour glass” sketch of human brain development, with a lull in genetic activity sandwiched between highly complex patterns of gene expression, said Sestan. Intriguingly, say the researchers, some of the same patterns of genetic activity that define this human “hour glass” sketch were not observed in developing monkeys, indicating that they may play a role in shaping the features specific to human brain development.
The findings emphasize the importance of the proper interplay between genes and environment in the child’s earliest years after birth when the formation of synaptic connections between brain cells becomes synchronized, which shape how brain structures will be used later in life, said Sestan. For instance, disruptions of in synchronization of synaptic connections during child’s earliest years have been implicated in autism.
The neocortex, Latin for "new bark," is our third, newly human brain in terms of evolution. It is what makes possible our judgments and our knowledge of good and evil. It is also the site from which our creativity emerges and home to our sense of self.
The Neocortex writes Carl Sagan in Cosmos, is where "matter is transformed into consciousness." It comprises more than two-thirds of our brain mass. The realm of intuition and critical analysis,--it is the Neocortex where we have our ideas and inspirations, where we read and write, where we compose music or do mathematics. "It is the distinction of our species," writes Sagan,"the seat of our humanity. Civilization is the product of the cerebral cortex."
Each cubic millimeter of tissue in the neocortex, reports Michael Chorost in World Wide Mind, contains between 860 million and 1.3 billion synapses. Estimates of the total number of synapses in the neocortex range from 164 trillion to 200 trillion. The total number of synapses in the brain as a whole is much higher than that. The neocorex has the same number of neurons as a galaxy has stars: 100 billion.
Researcher sestimate that with current technology it would take 10,000 automated microscopes thirty years to map the connections between every neuron in a human brain, and 100 million terabytes of disk space to store the data.
Self-aware, language-using, tool-making brains are very new in the evolutionary timeline, some 200,000-years old. Most of the neurons in the neocortex have between 1,000 and 10,000 synaptic connections with other neurons. Elsewhere in the brain, in the cerebellum, one type of neuron has 150,000 to 200,000 synaptic connections with other neurons. Even the lowest of these numbers seems hard to believe. One tiny neuron can connect to 200,000 neurons.
The image at the top of the page shows the neocortex organised into thousands of columns of neurons. Each column has a diameter of 0.5mm and contains 10,000 neurons. The neocortex is also organised into 6 layers. In the background are other neurons making up the neocortical column.
Mihovil Pletikos, Andre ́ M.M. Sousa, and Goran Sedmak of Yale are co-lead authors of the Yale study. Other Yale authors are Kyle A. Meyer, Ying Zhu, Feng Cheng, Mingfeng Li and Yuka Imamura Kawasawa.
The Daily Galaxy via Yale University
Imagae Credit: IBM/EPFL Blue Brain Project