Making Up Our Minds, The Pruning Process
By the age of three infants have adapted to their immediate worlds, their homes and families. Their neuronal connections have multiplied sevenfold. During specific windows of “early learning” called “critical periods,” specific neural pathways are forged, proliferate intensely, and are then maintained for life. As neural pathways become more used and “conditioned,” however, fewer neurons are needed. After the age of three, with brain pathways and circuits in place, a pruning process begins that efficiently discards unneeded connections.
A child’s total number of brain neurons then declines by 40%! Children have learned “the ways of the(ir) world” and become more “hard-wired.” After the age of three unused or unwanted neurons and their dendritic connections are selectively forgotten, or disappeared as fast as environmental activists in Central America. During certain stages of sleep the subconscious mind literally makes up our minds for us – deciding to keep or not to keep dendritic connections and neurons alike.
Stress can precipitate disease and is toxic to overall health, that we know, but it can even shrink the overall dimensions of the brain! That’s a depressing thought.
Chronic stress depletes the levels of serotonin, dopamine, and norepinephrine vital to maintaining mood. Stress can be work-related, from finances turned upside-down, from loss, trauma, police work, a breakup, divorce, or foreign war as with PTSD. Most often, chronic stress comes from the ongoing threats or conflicts we feel powerless to control. The prolonged sense of helplessness often associated with stress can trigger depression.
Effort (and Challenge) = More Stem Cells = More Serotonin = Better Moods
“Fresh neurons arise in the adult brain every day. New research suggests that the [stem] cells ultimately help with learning complex tasks—and the more they are challenged, the more they flourish.” – Tacey J. Shors, Rutgers University, 2009
The opposite of helplessness, the drive of regular “effort,” either mental or physical, stimulates the production of stem cells in the hippocampus (neurogenesis). Not only do greater numbers of stem cells in the hippocampus survive with regular effort, they also “flourish” in proportion to that effort. When greater numbers of stem cells reach maturity they produce higher levels of serotonin, that then produce better moods. Even in adult rats, 5,000 to 10,000 new hippocampal stem cells are created every day! No wonder so many yoga enthusiasts are signing up for those six-week intensives, teacher-certification courses. The increased stem cell production from six weeks of intensive effort and challenge transforms the body, physical brain, and the mind.
During depression, however, the production of neural stem cells is vastly inhibited. In chronically depressed patients, the hippocampus (the learning and memory area of the brain that shows greatest production of stem cells) shrinks in size. In the average person, living with challenges of everyday life, neural stem cells are constantly being generated in the hippocampus, then migrating to brain areas with the greatest need, to repair damage or bolster increased activity. Upon arrival, neural stem cells differentiate and integrate, making millions of new neuronal connections. After a single learning event, a snail neuron with just 1,300 dendritic connections will double its capacity, growing 1,400 new dendritic “spines.”