Neuroplasticity and neurogenesis

This entry is part 1 of 2 in the series The architecture of the human brain

Neuroplasticity and neurogenesis

Only a few decades ago, we were unable to help people improve their cognitive information processing skills because of a constraining belief that the brain was hard-wired to function in predetermined ways and could not be changed. However, recent brain research focused on neuroplasticity has demonstrated that the brain is “soft-wired” and can be modified: “with the right kind of stimulation and activity, the brain can dramatically change and remodel itself to become more efficient and effective in processing information” (Hardy, J.; Scanlon, 2009,p. 3). Additionally, a recent development in cognitive modifiability has demonstrated that the brain can be modified in predictable ways with proper training. These two revolutionary developments of our century have paved the way for innovative approaches in developing and enhancing cognitive skills.

The first recorded inference to neuroplasticity dates back to the 1700s, when the Swiss philosopher Jean-Jacques Rousseau suggested that the brain was continually being reorganized by experiences. Chopra & Tanzi noted: “this may have been the first declaration that our brains are flexible and plastic, capable of adapting to changes in our environment”(Chopra & Tanzi, 2012, p. 29). Johansson provided an extended definition of plasticity: “the concept of brain plasticity implies that the brain is adaptable, and includes all the mechanisms responsible for the brain capacity to change in response to incoming stimulations, our activities and thoughts” (Johansson, 2006, p. 50).

William James, who is also known as the father of experimental psychology, was the first to coin the word plasticity in the context of brain research as early as 1890. He argued that: “organic matter, especially nervous tissue, seemed endowed with very extraordinary degree of plasticity” (Begley, 2007, p. 5). Sherrington and Brown studying monkey cortex suggested that repeated, habitual movements “leave a physical trace in the motor cortex of the animal,…and these…were as individual as fingerprints” (Begley, 2007, p. 28). These researchers provided the first empirical evidence that “habits both produce and are reflections of changes in the brain” (Begley, 2007, p. 29). In 1915, Ivory Franz conducted the first research into neuroplasticity. His research provided evidence that each animal’s cortex was different. This finding led him to hypothesize that these differences probably reflected the unique motor habits and skills of each monkey (Begley, 2007, p. 29).

The first evidence demonstrating brain plasticity came from a series of experiments conducted by Karl Lashley in 1923. The researcher trained rats to seek food rewards in a maze and then progressively removed part of their cortex to assess the point at which learned behaviors will be forgotten. Results showed that the rats could successfully navigate through the maze even after 90 percent of their cortex was removed. Chopra and Tanzi explained this phenomenon as follows: “in learning the maze, the rats create many different types of redundant synapses based on all their senses. Many different parts of their brains interact to form a variety of overlapping sensory associations. In other words the rats were not just seeing their way to the food in the maze; they were smelling and feeling their way as well” (Chopra & Tanzi, 2012, p. 26).

These findings failed to catch the attention of researchers and practitioners until the Canadian psychologist Donald O. Hebb advanced the concept of use-dependent plasticity of the nervous system in his book  (Hebb, 1949). After conducting an experiment in which he exposed laboratory rats to an enriched experience, Hebb concluded that: “the richer experience of the pet group during development made them better able to profit by new experience at maturity—one of the characteristics of the ‘intelligent’ human being” (Rosenzweig & Bennett, 1996). For all intents and purposes, Donald Hebb can be considered the father of neuroplasticity, since he provided the first hypothesis explaining how the brain remodeled itself continually in response to experience. According to his hypothesis, “when neurons fire simultaneously, their synaptic connections become stronger, raising the chances that the firing of one will trigger the firing of the other” (Begley, 2007, p. 30). It was only years later that researchers started testing Hebb’s hypothesis that “cells that fire together, wire together”. Hebb’s work inspired many scientists and acted as a catalyst for further research in brain plasticity (Johansson, 2006) . Neuroscientists from the University of California were able to demonstrate through a series of experiments with monkeys that the experience involved in learning a skill can promote the rewiring of the brain regions to create new circuits (Chopra & Tanzi, 2012).

There are three possible scenarios that can take place with the synaptic connection during the information processing process: (1) new synapses may be generated; (2) some synapses may be pruned, and (3) some may be weakened. Information processed and integrated by the brain enhances the effectiveness of the synapses. Research indicates that: “when neurons fire simultaneously, their synaptic connections become stronger…much as traveling the same dirt road over and over leaves ruts that make it easier to stay in the tracks on subsequent trips, so stimulating the same chain of neurons over and over” (Begley, 2007, p. 30). It has been suggested that traces left by people processing the same information will be different and specific to each individual (OECD, 2007). There is now compiling evidence that “the brain is the child of experience, undergoing physical changes in response to the life its owner leads” (Begley, 2007, p. 31). The brain’s capacity to process information does not depend only on the density of neurons, but also on the “richness of the connectivity between them” (OECD, 2007, p. 37).

There is a significant amount of evidence today which indicates that the brain is capable of learning because of its flexibility. Since the human brain has already attained 90 % of adult size by the age of 6, there was a common assumption among scientists that these changes in the brain can only occur during childhood. Research evidence however indicates that changes in brain structure are triggered by experience and environmental stimulations (OECD, 2007), and that thoughts can also alter the brain. OECD has indicated that: “the concept of plasticity and its implications are vital features of the brain. Educators, policy makers and all learners will all gain from understanding why it is possible to learn over a whole lifetime and indeed brain plasticity provides a strong neuroscientific argument for “lifelong learning” (OECD, 2007, p. 30).

Although neuroplasticity is hailed as the greatest discovery of the century, Canadian psychiatrist Norman Doidge argued that neuroplasticity is a double-edge sword. While plasticity can promote the development of a more resourceful brain, it also makes the brain vulnerable to negative outside influences. He noted that disorders and poor habits are also the results of brain plasticity. Debriefing comments made by a student who participated in cognitive enhancement training illustrate how some students may have been victimized by the negative effects of environmental influence on brain plasticity in learning: “I was always told I am stupid. Now I feel smarter” (Chinien, C., Boutin, F., Letteri, C., Cap, O., Porozny, 1995).

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