The Death of Genetic Determinism?
I’m currently reading Sharon Begley’s fantastic book Train Your Brain, Change Your Mind, and wanted to take a few posts to summarize some of the concepts articulated throughout the book’s pages. Melding both science history and an optimistic vision of humanity’s potential, Begley’s book is a veritable ode to the phenomenon of neural plasticity.
The term neural plasticity refers to the capability of the brain to physically rewire and to, quite literally, become a new brain. Establishing neural plasticity as a scientific fact has been an arduous battle that has taken decades of work and that has fought head-on against previously prevailing scientific dogmas. For much of the twentieth century, the dominating doctrine of neuroscience was that once a baby is born, the neurons that are in the brain at the time of birth are all that there will ever be—there are no new brain cells that came into being in that individual from that point forward. This assumption, however, was invalidated by a conglomeration of clever experiments. One of the earliest of these crucial studies was a paradigm that tracked radiolabeled thymidine in the bodies of primates. In other words, thymidine—one of the four molecules that DNA uses for coding information—was labeled with a radioactive hydrogen isotope and injected into primates to determine whether or not the brains of these animals were creating any new neurons. If the primate brains were creating new brain cells, then the radiolabeled thymidine would appear inside of the DNA of the new neurons. If, on the other hand, primate brain did not create any new brain cells following birth (the belief that prevailed at the time) then the radiolabeled thymidine would not appear anywhere in the brain. Much to the delight of the scientists conducting these experiments, it was shown that—yes—thymidine with the labeled hydrogen had indeed been incorporated into the brains of the primates, indicating that the brain was generating new neurons, even after birth. This finding was tremendously significant, and opened up the door for myriad studies on how the brain changes—physically—throughout the course of life.
Fast forwarding a bit in the exciting narrative of brain plasticity, another victory was gained when it was demonstrated that not only can the brain generate new neurons during the course of its life, but that the brain can actually re-train neurons to perform tasks that their genetic code in no way intended them to perform. In 2000, a team of scientists led by Alvaro Pascual-Leone measured the brain activity of blind individuals while they were reading Braille. Because Braille is a system of language coding that utilizes the sense of touch in the fingers, one might expect that while blind persons are using their fingers to read Braille, that the brain regions typically reserved for tactile sensory input would be stimulated. Contrary to this expectation, however, Pascual-Leone and his team discovered that the visual cortex—the region of the brain normally processing the sense of sight—is involved in decoding and processing Braille when it is read by blind individuals. This finding is monumental in its implications. It was previously thought that because blind individuals do not utilize their visual cortex to process visual input, that the visual cortex in blind individuals would therefore be silent and unused. On the contrary, the brains of blind individuals were adapting the visual cortex to perform complex tasks not “intended” by nature. The use of blind individual’s visual cortex to process information from the fingers in tactile stimulation was a huge indicator of the brain’s ability to adapt and employ brain regions based not only upon genetic pre-coding, but also to recruit and model brain activity based upon experience and circumstance.
Stay tuned for more nuggets of neuroplasticity, including the questions of whether or not plasticity can occur in adult brains (as opposed to plasticity only occurring in the brains of children), summaries of the experiments that led to the answers for these questions, implications for development and training of character and disposition, and the vision and possibility of what brain plasticity may allow us to achieve together as a human species. Lots of good stuff yet to come.