This article is Part 4 of the 7-part series “The Ever-Adapting Brain”!
Organic matter, especially nervous tissue, seems endowed with a very extraordinary degree of plasticity.
Psychologist William James, 1890
By 1981, thinking had already begun to change when two psychologists working at Johns Hopkins, David Hubel and Torsten Wiesel, showed that the brain is capable of rewiring itself according to sensory input received during critical periods of development. Hubel and Wiesel received the Nobel Prize for their research in brain “plasticity” by showing that kittens deprived of vision in one eye during their first year of life would grow neural connections to compensate.
Within that critical period of their first year their one-eyed kittens had redirected the normal course of maturing neurons from their one good retina to the opposite side visual cortex, to both visual areas on each side of their brains. They had replaced missing input from the blind half of their vision and rewired themselves for life.
During the mid-1990s, researchers discovered that brain “plasticity” was not limited to critical periods. Immature stem cells in the adult hippocampus, the brain region most involved with learning and memory, were shown to constantly migrate and transform into all types of adult brain cells during all stages of life. Adult brain stem cells became integrated into all areas of the brain, growing millions of connections.
Stem cell research continued, showing that brain stem cells proliferated in large numbers, much larger than expected. As an ecological system, the brain responds to damage by replenishment, directing new stem cells to areas where stem cells are most needed, filling in for lost niches, and fortifying highly active neural pathways. A 2004 study revealed that consistent mental effort significantly increased the percentage of brain stem cells that reach maturation and integration.
With greater mental effort, greater numbers of immature stem cells migrate, differentiate, they integrate as mature brain cells in areas where they are most needed. Once in place they quickly sprout tens of thousands of bulbous dendritic spines with diverse interconnections. The multifarious connections of dendritic spines grow stronger with effort and learning, or wither away with disuse and selective forgetting.