Between birth and early adulthood, the brain passes through significant periods of neural growth and pruning in which new neuronal connections are produced and those not used are pruned. Throughout this development, you 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 individual can 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.
Throughout your adulthood you will find that your IQ is not likely to fluctuate as dramatically as before, because the process of neural growth and pruning slows considerably. By staying mentally and physically active, you can slow the decline of your fluid intelligence that begins its decline in early adulthood and augment your IQ with increased crystallized intelligence, keeping your “combined” IQ relatively stable. However, as you enter your senior years, your IQ (fluid plus crystallized intelligence) will decline more steeply and you may regress into the state that is facetiously called, “hardening of the categories.” That’s when your family and friends will perceive you as less open to new ideas or opinions.
*Ramsden, Sue. et al. 2011. “Verbal and non-verbal intelligence changes in the teenage brain.” Nature. Vol. 479. pp. 113-116.
