ScienceMasterIf it's your job to develop the mind,
shouldn't you know how the brain works?
What Is Brain Plasticity?
- Written by Kenneth Wesson Kenneth Wesson
- Published: 19 March 2003 19 March 2003
Alvin Toffler, the noted author said, "The illiterates of the future are not those who cannot read or write, but those who cannot learn, unlearn, and re-learn," but what happens inside of the human brain to foster those events commonly described as "learning," which is the goal formal education? In order to avoid being among those illiterates of the future, how should we modify our classroom instruction so that it conforms to the latest research findings concerning the brain?
Cortical plasticity refers to the brain ability to continue exercising its flexible nature by allowing different areas of the brain to change as a result of experiences it gets in the outside environment. The brain is sturdy, delicate and flexible. A child’s early interactions directly impact the ways in which the brain gets physically connected or how it gets "wired-up" initially. With the acquisition of new knowledge or any new learning, the elaborate networks and structures inside the brain go through modification, re-organization, or some degree of cellular alteration. Those changes are seen in the brain’s chemistry, structures and functions.
The good news about neurons is found in the notion of cortical plasticity, which occurs in certain areas of the cortex. It can literally change the functional qualities of various brain structures depending on the regularity and type of new tasks that neurons are asked to discharge. The bad news is that any seldom used or unused neural networks get unceremoniously "pruned" away during one’s early years. Particular skills can be lost forever, if they are not cultivated during especially sensitive time periods during the first years of life in particular. High levels of stimulation and numerous learning opportunities at the appropriate times lead to an increase in the density of neural connections (the dendrites) and more brain real estate devoted to an emerging talent. Howard Gardner’s theory of Multiple Intelligences identifies eight forms of human intelligence. Each of these intellectual comes with a matching primary area of the brain that (1) houses the cortical representations, (2) executes the motor outcomes, and (3) is connected with its myriad associated areas (see figure 5)
Figure 5- Multiple Intelligences Type of Intelligence Location or Primary Brain Area
- Linguistic Left hemisphere, frontal lobes and left temporal lobe (Wernicke’s area and Broca’s area)
- Spatial Right hemisphere (posterior temporal region)
- Logical-Mathematical Left parietal lobe and right hemisphere
- Interpersonal Right frontal lobe, right temporal lobe and the sub-cortical structures in the limbic system
- Bodily-Kinesthetic Motor cortex, basal ganglia, and the cerebellum (automatic motor skills)
Intrapersonal Both left and right frontal lobes, the (sub-cortical) limbic system, and the right parietal lobe
- Musical Right temporal lobe
None of these intelligences will unfold naturally until the appropriate environmental conditions are present to allow it to develop and mature. In a model environment, the talents can be maximized with the cooperation of the appropriate gene set.
At the earliest stages of infancy, not only are all children biologically ready to learn from their stimulating environment and their interactions with other people, early brain development requires this. Healthy brain cells will perish if they fail to find a job to carry out during these critical early developmental periods. The lack of visual stimuli during infancy can permanently rob a healthy eye of its ability to see. If a child does not hear words by age of ten, he will have a difficult time learning to speak any language at all. Neurons that should have participated in the language processing, but instead find themselves lacking a role to play have only one of two options. They will be recruited to support another function with different neural circuit devoted to a contrasting specialty, or they will experience apoptosis, cell death. In brain terms, neuronal death occurs by way of a self-induced cell-suicide. In the case of language, the remaining brain cells that specialize in language processing are well-fed and well-nourished for most of one’s entire life. The others are gone and gone forever.
The ways in which the brain is stimulated (or not stimulated) in will determine the cortical complexity of any region in the brain, which is measured by the number of synapses and the nature of their connections to the various other parts of the brain. Brain cells constantly rearrange their one quadrillion-plus connections in response to extrinsic circumstances. All new learning, the external or internal stimuli that the brain encounters, promotes additional changes in the brain. In doing so, areas of the brain can adapt to any surroundings, quite different from other animals which operate solely by instinct and do so only within specialized limited environments. Human brains can adopt new functions based on the quantity and the quality of input received and processed by the brain.
In the 1980s, UC Berkeley’s Mark Rosenzweig discovered that a rat's environment affected both the weight of its brain, as well as the quantity and density of connections between and among its neurons. These are considered the best indicators of a rat’s ability to learn new skills or information. Boosting the immature brains with excessive amounts of growth hormones can also increase the number of neurons in rats.
In human beings, however, one’s level of expertise shows itself through major differences in the neural representations of the same information. When we compare brain-images of "novices" and "experts" performing the same task, or game, their differences are vividly apparent. Experts organize and interpret information in their brains in ways that are different from non-experts and, following input, that information is represented differently in their brains. Cortical differences are observable in the neural networks accompanying the development of a specific talent that an individual cultivates over time.
In music and in the game of chess, the "masters" develop elaborate semantic memory systems that permit a wide variety of ways to demonstrate the manner in which information is processed by their brain as compared to a novice. When comparing three pianists with varying experiences, we can observe distinct cortical differences in their brains. The pianists are (1) a 30-year-old pianist, who began piano lessons at the age of four, (2) a 30-year old pianist, who casually took up piano at age twenty-eight, and (3) a highly motivated 9-year old novice, who has been playing piano for slightly less than a year. All three pianists can play the exact musical piece, where the song is indeed the same, but each of the three performances shows completely different neuronal activities taking place inside their brains.
The areas in their brains that represent finger movements (the motor cortex) in each hemisphere of their brains will be different. The regions of the cortex that handle the reading of musical notations will also be different. Different neurophysiological circuits represent the different aspects of how that particular song will be processed in their brains and preformed by their bodies, but they will all reflect profound differences seen in each brain. These contrasts will be apparent, as each individual initiates a different set of signals for the execution of different physical commands, although they are all playing precisely the same song after reading exactly the same musical notes. The exchange of particular "musical performance" neural data flows more freely between the cortical areas of the brain in the more adept and well-trained brain. The attentional efforts are considerably less for the expert. The cortical differences can now be seen both in the performance quality as well as through brain imaging techniques.
In an experiment, expert chess players and novices were asked to memorize random chess pieces on a board. Under these conditions, the experts performed no better than the novices. However, when the chess pieces were in "game positions" that might replicate positions if two players were in the midst of a challenge, the experts’ recall of the location of each chess piece far exceeded that of a novice. The ways in which the accomplished players organized the information was clearly unlike the emerging talents of players with no prior chess experience.
Novice teachers and experienced educators will scrutinize the same classroom events and assign contrasting instructional significance to many of them. When at home or outside of her class, encountering information that can potentially improve preparation and instruction will likely be recognized by the expert teacher, but not her newer counterpart. How varied are these educators’ brains?
We see identical events taking place in reading and language arts classes. There are students with natural advantages in linguistic skills (girls), sitting next to students with limited experiences in the language spoken in class (foreign born), as well as children who have had absolutely no personal experiences that relate to the contents of the story (where the story is about yachting and a student’s limited inner-city life has never taken him to a harbor, let alone sailing on a boat of any kind). These students can be contrasted with those whose parents read to them at a very early age and who also demonstrate a more sophisticated usage of the language. (Age is an equally crude indicator of intellectual, motor, maturational development, since each brain develops on a different timetable).
The manner in which fictional stories will be processed in the brains of students in each of these groups will vary drastically, as will the level of detail in recalling a story and its composing elements. Meaning is not conveyed; it is evoked. Activating the appropriate neural pathways for reading and understanding a given passage assumes that a child has already developed the corresponding schema (the necessary background knowledge) fostering those neural connections. The human cortex operates best by patterns not by facts. But the patterns must make sense or the individual facts are the first recall casualties. Information that is difficult to comprehend or that has no meaningful context for an individual’s neural networks will be information that is difficult to remember. As a result, the idiosyncratic human brain and the manner in which we deliver formal instruction reveal major design errors. These known facts partially explain the successes seen in smaller classes particularly in the primary grades.
The experiential paradigms of two people might offer a similar contrast. Should they watch the same movie about a man escaping through the jungle, one might say that the film is entertaining, while the other finds it quite disturbing. Knowing that the latter individual survived the Khmer Rouge in Cambodia (the "Killing Fields") will help understand the differences in processing the same movie at the same time. When a class of students reads the same material, although the words and pictures are the same, the vast range of individual cortical representations and brain circuitry gives us a new level of understanding why some students relate to the material differently and some remember it considerably better than others. The neural representations to which the new material is connected inside the brain makes comparing one student’s performance with another for grading purpose an effort that defies logic. Such a system for grading students has all of the trappings of fool’s gold. We live and exist in completely different cognitive world’s that have shaped ours into distinctly different brains that defy these simplified comparisons.
The traditionally accepted position was that once neurons were lost, they were lost permanently and new neurons were never re-generated in the human brain. That belief is beginning to show ever widening cracks. For the past several decades, scientists believed that brain cells were a finite resource; that unlike other cells in the body, those in the brain did not reproduce. In spite of this eons-old "neuro-dogma," new evidence is suggesting otherwise.
Just as a blossoming young child goes through growth spurts, there seems to be a similar set of events occurring in the brain. The human brain appears to undergo surprisingly dramatic anatomical changes (fostering corresponding behavioral modifications) during seven key periods.
1. The first is the delicate brain-building and subsequent purging (where the least-used cells and circuits die out) processes, during the prenatal stages months. Prenatal substance exposure can trigger a disruption in any of these important early processes resulting in long term brain impairments (e.g., FAS- fetal alcohol syndrome and deficits caused by poor early nutrition).
2. Adjustments to a specific kind of environment drive the early postnatal brain alterations, during the first year of life. Here, important systems get switched on or not depending on the nature of the sensory input received from the environment.
3. Fine-tuning of skills takes place between the ages of three and six. Around 5 or 6, the brain has reached 90-95% of the average adult volume and is 4 times larger than it was at birth. These are the years when extensive internal re-wiring takes place in the frontal lobes (involving organizing actions, planning activities and focusing attention).
4. Between the approximate ages six and puberty, the parietal lobes begin to show a great amount activity. During this time, the skills for developing language and spatial relations reach their construction "peak." At the end of this period, the impressive growth and connecting rate falls off quickly. After puberty, mastering a new language becomes enormously challenging.
5. Immediately prior to puberty, another spurt in brain cell activity takes place in the frontal lobe (at age 12 in boys and a year earlier in girls). These neural construction projects are suddenly and strangely placed on hold and there is a substantial loss in the frontal lobes for a decade beginning in the mid-teen years.
6. Wholesale renovations take place during puberty and the teen years (hormonal changes, alterations in the body’s biochemistry, physical growth spurts, etc.). These massive changes are so incapacitating that there is now an increasing awareness of why teen-agers (along with chemotherapy patients) need to sleep longer, which more than justifies a later starting time for middle and high school students.
7. The last stage is adulthood, where (although the size of the brain remains the same) the trillions of connections in the brain continue to rearrange themselves constantly throughout our years as parents, workers, job-changers, spouses, etc. in our ongoing effort to adjust to our life, environment and circumstances. That the adult brain makes such neurophysiological changes is shattering many of the traditional assumptions about neural development in humans.
In the late 1960s, neurogenesis was discovered in the olfactory bulb, which houses the neurons responsible for processing the sense of smell. Later, researchers found that the hippocampus also replaced its neurons. The hippocampus receives partially processed sensory input from the sensory systems of the PNS and processes it into tiny morsels digestible by the memory-storage areas of the cerebral cortex. Neurons in the olfactory bulb were replaced almost monthly. In the hippocampus, brain cells were lost and restored at a much slower rate. Over the course of a lifetime, all of the neurons in our hippocampus are replaced 2-3 times.
For years, there were hints that neurogenesis might take place in humans. In the 1990s, researchers detected neuronal growth in canaries that were learning new mating songs. Just as young children must hear language before they can produce spoken words, young "normal" (neurologically and sexually healthy) male canaries must hear songs and develop the appropriate neural circuits for processing canary mating songs before they can sing them. Researchers found that the male cortex changes seasonally in order to produce the appropriate songs, but only as long as they are useful. When the cerebral cortex of canary female fetuses and young females were injected with male hormones, their brains also changed into "male" brains, and they were able to sing mating songs like their male counterparts who had been born as male birds.
Neurogenesis does occur in the hippocampus of adult macaque monkeys, which are phylogenetically very close to humans, since both species are Old World primates and have identical hippocampal structure and function. Researchers reported last year that in adult macaques, new neurons are added to three neocortical association areas (the prefrontal, inferior temporal and posterior parietal cortex), which are important in cognitive functioning
A generation ago, we would cautiously speculate about these neural activities and the corresponding structural transformations. At that time, our best evidence came by way of investigations permitted only due to misfortune or through autopsies following death. Today, not only can we observe brain plasticity, but we can also capture it pictorially with non-invasive brain-imaging techniques using perfectly healthy subjects, where we leave neither side effects nor scars.