The Brain's Growth
By Silvia Helena Cardoso, PhD

Did you know that every time you learn something or acquire a new experience your brain's cells suffer a modification, and that modification will be reflected in your behavior?

For example, if you have ever walked through a street during the night and perceived that there were people looking like criminals, you would have avoided going through that street again. Or, a child who gets an electrical shock after inserting his or her finger in an outlet, will never repeat that behavior again. In these examples, the behavior was modified as a result of an experience.

The neurons in the cerebral cortex, the outer layers of the cerebral hemispheres, deals with higher cognitive processing. It exhibit an impressive amount of plasticity and every part of the nerve cell from soma to synapse alters its dimensions in response to the environment.

The human brain hemispheres are covered in its greater part by an external layer of gray color called cerebral cortex. A deep cut into the brain would show that this gray surface has a thickness varying from 1 to 4 mm. Its largest part is composed by nerve cells (neurons) which receive impulses from distant points from the body retransmiting them to the right destination. The brain carries out highly diversified functions, and because of that, the cells that constitute it are also specialized. Different types of neurons are distributed across different layers in the cortex in arrangements which characterize the several areas of the hemispheres, each one with their own functions.
Each neuron contributes to behavior and to each mental activity, producing or not electrical impulses.

What is growing? The dendrites of the nerve cells are responsible for most of the neocortical growth, and the neural network they form becomes the "hardware" of intelligence (1). Dendrites are extensions of the nerve cell membrane that receive the input from other nerve cells. These branches are very responsive to such input, increasing in number with use and decreasing with disuse. The phrase "use it or lose it" definitely applies to this process. In Wernicke's area, which deals with word understanding, the nerve cells have more dendrites in college-educated people than in people with only a high school education.

Increases in cortical growth as a consequence of stimulating environmental input have been demonstrated at every age, including very old age. The greatest changes, however-as much as 16 percent increases-have been noted during the period when the cerebral cortex is growing most rapidly --the first ten years. By providing children with challenging experiences through enriched education and environments, those dendrites cannot help but be off to a good start (1).



Since no two human brains are exactly alike, no one enriched environment will completely satisfy all learners for an extended period. The range of enriched environments for human beings is endless. For some, interacting physically with objects is gratifying; for others, finding and processing information is rewarding; and for still others, working with creative ideas is most enjoyable. But no matter what form
enrichment takes, it is the challenge to the nerve cells that is important. Data indicate that passive observation is not enough; one must interact with the environment (1). One way to be certain of continued enrichment is to stimulate and maintain curiosity throughout a lifetime.

The cellular alterations resulting from learning and memory are called plasticity. They refer to an alteration in the efficiency of the synapses that can increase the transmission of nervous impulses, thus modulating behavior.

An experience can happen through an active learning, or by living in an rich environment that includes other individuals, colors, music, sounds, books, smells, etc.

It was also possible to demonstrate in scientific laboratories that a rat's brain presents a much greater number of brain cells interconnected to each other when they live together in a cage filled with toys as wheels, balls, etc., than rats living in a cage alone and without anything to do or learn.

Donald Hebb, from Montreal, and Jersey Konorski, from Poland, some of the major experts on the phenomenon of learning and memory in the 40's, were the first ones to believe memory should involve changes or increases of nervous circuits.

Nervous circuits are sets of brain cells (or neurons) that communicate to each other through junctions called synapse.

When a cell is activated, it is triggered the liberation of chemical substances in the synapses, called neurotransmitters, becoming them more effective. Research has found that neurons that are more "exercised" bear a greater number of ramifications dendrites communicating with the dendrites of other neurons. Thus, for memory to be established, it is necessary that nervous cells form new interconnections and produce new protein molecules.

1. Marian Cleeves Diamond - The Brain . Use It or Lose It - Mindshift Connection (vol. 1, no.1), Dee Dickinson (ed.).  Zephyr Press publication.

The Author

Silvia Helena Cardoso, PhD. Psychobiologist, master and doctor in Sciences, Founder 
and editor-in-chief, Brain and Mind Magazine, State University of Campinas. 


Copyright 1997 State University of Campinas