3.3 The Plasticity of Intelligence:

“When Cajal made our first study of brain cell organization in the 1880s, he was struck by  the plasticity of the brain, which, as we have just mentioned, is the ready ability of neurons to reorganize themselves. More recently we became aware of neural decay, and as we have seen this helped to prompt the belief in critical periods. However, we are now beginning to understand that Cajal may have had more insight than has been realized, for as our  technology ever increases so are we beginning to realize the ability of neurons to regenerate themselves.

Accordingly, it has become realized that neurons can re-grow an axon that has been removed, and there is increasing evidence that the central nervous system does have an inherent capacity to regenerate. myelinating cells. Instances have been discovered where certain types of neural damage have been repaired by spontaneous remyelination. Myelin, we may recall, is the fatty sheath that insulates a nerve cell and enables it to conduct a signal. When this sheath breaks down, as it does through hereditary metabolic disorders such as adrenoleukolystrophy (as was the case with the child in the film Lorenzo’s Oil), or through acquired diseases such as multiple sclerosis, nerve cells fail to conduct their signals to each other and a break down of the nervous system arises. It was in seeking to combat this excessive demyelination, that research in the nervous system showed the possibility of reversing this process by transplanting myelin producing cells from the Peripheral to the Central Nervous System. Such Schwann cells have been found to reproduce themselves when placed in the CNS with the ability to migrate to the defective myelin cells and repair them. Knowledge such as this, aided with reports that the drug metformin used by diabetics has the capability to cause new neurons to form, helps us to understand how neurons may repair themselves and grow to repair existing circuitry or create new circuitry if the conditions allow. When we discuss this sense of flexibility, which again emphasizes the unknown property of the gene, we find ourselves returning to the image of brain plasticity that Cajal so strongly advocated.

It is not then, that the brain is fixed in its orientation, or that critical periods exist as Hubel and Wiesel claimed for vision, and as Lenneberg believed for language. In consequence, there are no critical periods for music, mathematics, or any aspect of intelligence…..