Human learning is driven by different groups of cells in the brain firing together. For example, a young child recognizing a dog sets off a coordinated response to the cells that encode the features of a dog — four legs, fur, a tail, etc. — and she will eventually be able to identify dogs going forward. But we also know that brain wiring begins before humans are born, before they have experiences or senses. In a new study in Science, Yale researchers identified how brain cells form this wired network in early development, before experiences shape the brain.
Cells That Fire Together, Wire Together
In the study, the researchers simultaneously measured the activity of a single retinal ganglion cell in mice, the anatomical changes that occurred in that cell during development, and the activity of surrounding cells in awake neonatal mice whose eyes had not yet opened. It turns out that very early development follows the same rules as later development — cells that fire together wire together. But rather than experience being the driving force, it’s spontaneous cellular activity.
Previous research has shown that before sensory experience can take place — for instance, when humans are in the womb or, in the days before young mice open their eyes — spontaneously generated neuronal activity correlates and forms waves. In the latest research, scientists discovered that when a single cell's activity was closely aligned with random bursts of activity from nearby cells, the cell's axon — the component that links to other cells — developed additional branches. Conversely, when the activity was not well-coordinated, the axon branches were removed instead. “That tells us that when these cells fire together, associations are strengthened,” said Liang Liang, co-senior author of the study and an assistant professor of neuroscience at Yale School of Medicine.
Hebb's Rule in Early Brain Development
This finding follows what’s known as “Hebb’s rule,” an idea put forward by psychologist Donald Hebb in 1949; at that time Hebb proposed that when one cell repeatedly causes another cell to fire, the connections between the two are strengthened. “Hebb’s rule is applied quite a lot in psychology to explain the brain basis of learning,” said Crair, co-senior author of the study and the William Ziegler III Professor of Neuroscience at Yale School of Medicine. “Here we show that it also applies during early brain development with subcellular precision.”
Several other neural circuits, including in the spinal cord, hippocampus, and cochlea also develop with spontaneous activity. While the specific activity pattern would be different in each of those areas, similar rules may govern how cellular wiring takes place in those circuits, said Crair. Going forward, the researchers will explore whether these patterns of axon branching persist after a mouse’s eyes open and what happens to the downstream connected neuron when a new axon branch forms.
StepUp Note
StepUp to Learn is a neural network approach to learning. It strengthens our neural networks by synchronizing the neurons that connect our vision, hearing, balance and movement. StepUp software programs turn basic skills into fluent skills, and turn fluent skills into tools for new learning.
Note by Nancy W. Rowe, MS, CCC/A
Reposted from Yale University
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