Thought for the Day: I must remind myself to spend more time researching my trivia facts before posting the question. On Tuesday, I asked:
At what age humans have the largest number of brain cells? a) 5 years old b) 45 years old c) 30 years old d) 2 years old e) 18 years old
The answer, d) 2 years old, was based on a fact I found a while ago on Likes.com which said:
Humans have more brain cells at the age of two than at any other time of their lives. What happens then, is the brain kills off the cells it deems unnecessary for the future. When people are telling you that the first couple years of a kid's life are their most important, they aren't really lying!
After I posted it, a follower, Enaa Aussen from google+, wrote:
Yesterday 12:39 PM
So I began to question the oversimplified fact I found on Likes.com. I should have known better, since I continuously tell you that there is really no trivial psychology. There are multiple interpretations of most "facts" in the field.
So here are a few quotes from articles about the development of the human brain:
In an article called, Children and Brain Development: What We Know About How Children Learn, Judith Graham, Extension human development specialist & Leslie A. Forstadt, Ph.D. Child and Family Development Specialist write that,
"At birth, a baby’s brain contains 100 billion neurons, roughly as many nerve cells as there are stars in the Milky Way, and almost all the neurons the brain will ever have. The brain starts forming prenatally, about three weeks after conception. Before birth, the brain produces trillions more neurons and “synapses” (connections between the brain cells) than it needs. During the first years of life, the brain undergoes a series of extraordinary changes.In the brain, the neurons are there at birth, as well as some synapses. As the neurons mature, more and more synapses are made. At birth, the number of synapses per neuron is 2,500, but by age two or three, it’s about 15,000 per neuron. The brain eliminates connections that are seldom or never used, which is a normal part of brain development."
In an answer to the question, "Are You Born With All Your Brain Cells Or Do You Grow New Ones?" Pasko Rakdic, Professor of Neuroscience and Neurology at the Kavli Institute at Yale University writes that:
"Shortly after birth in humans, a substantial number of new nerve cells are produced and added to brain regions called the cerebellum, olfactory bulb, prefrontal cortex, and hippocampus. But by age 2, neurogenesis in most of these regions disappears except in the hippocampus — a region involved in learning and memory. This may be the only location in the brain where new cells are added throughout one’s lifetime. ...The fact that the majority of our neurons are as old as we are might be what allows us to remember our history and build civilization."
FAQ Zero to Three http://www.zerotothree.org/child-development/brain-development/faqs-on-the-brain.html#experience
In FAQ on ZerotoThree.org's page an explanation of pruning of neurons around age 2 is given in this way:
"Those (Neurons) that are consistently turned on over time will be strengthened, while those that are rarely excited may be dropped away. Or, as neuroscientists sometimes say, "Cells that fire together, wire together." The elimination of unused neural circuits, also referred to as "pruning," may sound harsh, but it is generally a good thing. It streamlines children's neural processing, making the remaining circuits work more quickly and efficiently. Without synaptic pruning, children wouldn't be able to walk, talk, or even see properly."
So although at age 2 years we may have the largest number of brain cells, it does not account for the growth of connections & synapses between brain cells which continue at a rapid rate in early childhood into adolescence. There are also findings that some parts of the brain continue to grow cells throughout our lives albeit at a much slower pace.