An evolutionary asset of the human brain is its adaptability. By the time you emerged from your mother’s womb, your brain contained about 100 billion neurons ready and waiting to connect with each other in response to the sensory experiences of your infancy. During your first two years on the planet, the neurons in your brain connected, in what are called synapses, at the rate of about 2 million per second, so that by age 2, your brain had about 100 trillion synapses–twice the number you have now.
Neural Pruning
Unable to sustain the biochemical reactions across all these synapses, your brain entered a stage known as neural pruning, removing the synapses for which there was little use. Your brain was fine-tuning itself to function effectively in the environment into which you were born. So much in this early stage of your brain development determined who you are today.
In the years following infancy, your brain continued to restructure itself in accordance with environmental stimuli. Early demands for certain types of cognitive tasks such as, learning a language or counting, played a role in determining which cognitive capacities would become most highly developed. Stanford University neurologist David Eagleman observes:
In a sense, the process of becoming who you are is defined by carving back the possibilities that were already present. You become who you are not because of what grows in your brain, but because of what is removed.
The Development of the Brain through Adolescence
The next dramatic phase in your brain growth occurred just before puberty when a proliferation of neurons and synapses appeared in your prefrontal lobe. This is the part of the brain associated with rational thought and executive function. A late phase in the evolution of the human brain, it provided you with a capacity for problem solving, deductive thinking, and drawing inferences–processes typically described as “higher order thinking skills.”
Another round of rapid and extensive production of neurons and synapses followed by extensive neural pruning, occurred when you entered puberty, significantly modifying and restructuring your neural network. By the end of adolescence, the pruning resulted in a decrease of between 5 and 10 percent of your brain mass, but your brain had efficiently attuned itself to the environment in which it would need to function. See contours of the prefrontal cortex at: Neurons & Synapses Throughout this development, we might expect that your IQ would remain relatively stable, because IQ is a measure of intelligence relative to others of the same age. However, recent research indicates that while the average IQ of those in the same age cohort is relatively stable over a span of several years, the IQ of an individualcan change significantly during this period. In a longitudinal study, 33 teenagers of average age 14.1 years were administered an IQ test and a structural brain scan in 2004 and then again in 2007, when their average age was 17.7 years. It was found that during this period, the average IQ of the group had changed very little; however about 20% of the participants showed a positive or negative change in IQ of at least 15 points (one standard deviation). Furthermore, magnetic resonance imaging (MRI) revealed that positive changes in IQ corresponded to increased gray matter in sections of the brain associated with those cognitive functions. Summarizing their findings, the researchers reported:
Our results emphasize the possibility that an individual’s intellectual capacity relative to their peers can decrease or increase in the teenage years. This would be encouraging to those whose intellectual potential may improve, and would be a warning that early achievers may not maintain their potential.
Indeed, during the simultaneous processes of rapid neuron growth and pruning from infancy through adolescence, your brain was in constant flux, changing your personality, your habit of mind and who you are. That’s why the “you” who entered high school is very different from the “you” who graduated university. Your ideas, beliefs, and manner of thinking were changed dramatically by your experiences and intellectual challenges as axons grew and connected neurons forming a complex network of interconnections. Emerging from adolescence like a butterfly from the pupa, you came fully equipped with an adult brain–a neural network containing your sense of self, your passions, your instinctive behaviors, your beliefs, and your capacity to learn.
So the bottom line in this discussion about research on brain use may be captured in the adage, “Use it or lose it.” That is why education, especially in the early years is so important. Each individual has a significant capacity for expanding their intellectual scope, but it must come from engagement in cerebral activities.
