Synapses and Plasticity

When a child is born, its brain, unlike most of its internal organs, has not fully developed.  In fact, at birth the brain is only 25% of its adult weight.   However, by age 2, the brain has grown to an astounding 70% of its adult weight (Berk, Child Development).  To explain this great gain in brain weight, we must dig deep to the microscopic level and examine the connectors between brain neurons, or synapses, that are key to the developing brain and its plasticity.

In the prenatal stage, the brain primarily produces brain neurons, or the cells that store information in the brain.  So, by the time a baby is born, it’s many neurons are ready to go, but the communicators between the neurons that lead to more advanced abilities- synapses- have not been widely developed.  But, once the baby is born and is exposed to many kinds of stimulation, synapses start to form at a fantastic rate, a rate in which even extra synapses form (Berk, Child Development).  However, like we learned in class, if you don’t use your synapses, you will lose them, a term called synaptic pruning.  In our book, they give a good visualization for this process, saying our brain is like a sculpture, and through synaptic pruning we sculpt away excess material in our quest for higher development.  In fact, our brain sculpts away nearly 40% of synapses during childhood (Berk, Child Development).

At age three the synapses in the brain are the most highly concentrated.  Although this does not mean this is the smartest a human being will ever be, this does mean brain synapses and brain plasiticity will never be higher.  This is because as the brain cuts off connections between neurons, it makes it so the brain runs more efficiently, although at the cost of losing plasticity.  Brain synapses and brain plasticiy are highly related, as we can see that after about age three to four (when synapses are most concentrated), a child starts to hit critical points and loses plasticity.  This is probably most evident in language, as children start pruning synapses at age 1 when they lose speech sounds, and at age 5, a child hits a language critical point.

This relationship is easily seen in many studies.  For exapmle, the study on Romanian orpahage children on pages 167-168 of our book shows that the longer these chilren went without stimulation (which synapses are made from), the lower they scored on placement tests.  Another example is that of a feral child named Genie, who was found at age 13 as a neglected girl who was never taught to speak.  When social workers found her and tried to teach her to speak English, she was highly disabled, and has never been able to speak normally(  This is depressing, yet a perfect example of the relationships between synaptic pruning, brain plasticity, and even critical points.

The development of synapses and synaptic pruning (which also leads to lower brain plasticity) is definately a good thing though, as without it our brains would be much more inefficient and humans much less intelligent.

Mike Angerbauer


~ by Mike Angerbauer on September 18, 2009.

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