Brain Development and Neural Plasticity*
A great deal of brain development happens prior to birth, and by the time the baby is born the brain is proportionately the largest part of the body. At birth the brain weighs about 25 percent of its adult weight. Compared to the rest of the newborn’s body, the brain is very heavy (the average newborn weighs about 7 ½ pounds, which is about 5 percent of adult size). At age 2, the brain weighs about 75 percent of its adult weight, and by age 5 it weighs about 90 percent of its adult weight. What accounts for this tremendous increase in weight? Certainly not new neurons because neurons are not made after birth. The increase is primarily due to myelination of neurons and synaptic growth in different areas of the brain.
Asynchrony in Brain Development
At different times, different regions of the brain experience growth spurts in synaptic connections. For example, immediately after birth, the axons and dendrites in the visual cortex will grow and make countless synaptic connections – way more than will ever be needed. This is called overproduction. Then, synapses are gradually pruned off and lost. So by age 5, the visual cortex is essentially complete. Similarly, during the first year of life there is a growth spurt in the motor cortex, the brain region responsible for moving the body. This growth spurt lasts several years, which explains why a newborn baby is not able to life its own head but can walk and run by age 2. These growth spurts in different regions of the brain continue all the way through adolescence and into early adulthood.
Research on Brain Development
So judging by brain weight, most brain development happens very early in life, leaving some to argue the first two years of brain development are the most important. However, using brain weight to gauge growth is a crude index, one that does not take into account a host of other features…
…animal studies have been a rich source of information about brain growth. For example, in the early 1960s studies on adult rats were conducted by psychologist Mark Rosenzweig and his colleagues. The researchers placed rats in enriched and deprived environments. An enriched environment was a cage with a water bottle, a food source, a running wheel, toys, and other rats. The deprived environment was smaller and had no running wheel, no toys, and no other rats. When rats from the two groups were compared in this study (and in subsequent studies), it was found that rats from enriched environments learned to run mazes more quickly than rats from deprived environments. Moreover, autopsy showed that their brains were heavier and exhibited more folds (an indicator of more extensive brain growth).
Human research has supported the findings of this research with rats. In the late 1990s brain researcher Charles Nelson discovered that large numbers of children in Romania were in state-run orphanages that provided basic needs (such as food and shelter) but provided virtually no social, emotional, or physical stimulation. Compared to other children these orphans smiled and laughed less, had poorer language skills, exhibited lower intelligence and higher rates of mental illness, and showed less brain activity. In 2001 Nelson and his colleagues began The Bucharest Early Intervention Project, a project designed to remove children from these orphanages and place them in foster families. They began by recruiting and training as many foster parents as possible. Children between 6 months and 2 ½ years were placed with families. The researchers continue to follow the development of the children with foster families as well as children of the same age still living in the orphanages. Those with foster families have made greater gains in language, intelligence, social skills, and most aspects of mental health.
In another series of groundbreaking studies, David Hubel and Torsten Wiesel studied the brains of kittens. In some of the studies they anesthetized the kittens and inserted microelectrodes into their brains to see which brain cells were working when the animals looked at different images. In other studies they examined kittens with one eye stitched closed for different lengths of time. They found that a cat’s visual system is wired to work at birth but will atrophy or waste away if not used. Cats that did not use their eyes lost the neural connections in the visual cortex. Hubel and Wiesel concluded that cats had to use their eyes in order for brain cells in their visual cortex to maintain the connections that were present at birth. This was science’s first clear evidence of neural plasticity; because of their research, Hubel and Wiesel won the 1982 Nobel prize awarded for work in physiology or medicine.
Neural plasticity is the term used to explain that neural connections can be altered through experience. Plasticity refers to flexibility, and the main idea behind this concept is that that the brain works in accordance with the “use-it or lose-it” principle. Neural connections and pathways used over and over are strengthened, but connections and pathways never or seldom used atrophy and are lost. For example, the brain at birth is wired to hear evert phonemic sound in every human language. If children hear sounds from only one language, the pathways for the phonemes in that language are strengthened, but pathways for other phonemic sounds are lost. So an adult who was raised hearing only English will have difficulty hearing phonemes unique to Japanese or Russian because those neural connection were never stimulated and were lost. Moreover, that adult will hear a second language through the filter of his or her first language. This is why most adults who learn a second language speak it with an accent.
At different times, different regions of the brain experience growth spurts in synaptic connections. For example, immediately after birth, the axons and dendrites in the visual cortex will grow and make countless synaptic connections – way more than will ever be needed. This is called overproduction. Then, synapses are gradually pruned off and lost. So by age 5, the visual cortex is essentially complete. Similarly, during the first year of life there is a growth spurt in the motor cortex, the brain region responsible for moving the body. This growth spurt lasts several years, which explains why a newborn baby is not able to life its own head but can walk and run by age 2. These growth spurts in different regions of the brain continue all the way through adolescence and into early adulthood.
Research on Brain Development
So judging by brain weight, most brain development happens very early in life, leaving some to argue the first two years of brain development are the most important. However, using brain weight to gauge growth is a crude index, one that does not take into account a host of other features…
…animal studies have been a rich source of information about brain growth. For example, in the early 1960s studies on adult rats were conducted by psychologist Mark Rosenzweig and his colleagues. The researchers placed rats in enriched and deprived environments. An enriched environment was a cage with a water bottle, a food source, a running wheel, toys, and other rats. The deprived environment was smaller and had no running wheel, no toys, and no other rats. When rats from the two groups were compared in this study (and in subsequent studies), it was found that rats from enriched environments learned to run mazes more quickly than rats from deprived environments. Moreover, autopsy showed that their brains were heavier and exhibited more folds (an indicator of more extensive brain growth).
Human research has supported the findings of this research with rats. In the late 1990s brain researcher Charles Nelson discovered that large numbers of children in Romania were in state-run orphanages that provided basic needs (such as food and shelter) but provided virtually no social, emotional, or physical stimulation. Compared to other children these orphans smiled and laughed less, had poorer language skills, exhibited lower intelligence and higher rates of mental illness, and showed less brain activity. In 2001 Nelson and his colleagues began The Bucharest Early Intervention Project, a project designed to remove children from these orphanages and place them in foster families. They began by recruiting and training as many foster parents as possible. Children between 6 months and 2 ½ years were placed with families. The researchers continue to follow the development of the children with foster families as well as children of the same age still living in the orphanages. Those with foster families have made greater gains in language, intelligence, social skills, and most aspects of mental health.
In another series of groundbreaking studies, David Hubel and Torsten Wiesel studied the brains of kittens. In some of the studies they anesthetized the kittens and inserted microelectrodes into their brains to see which brain cells were working when the animals looked at different images. In other studies they examined kittens with one eye stitched closed for different lengths of time. They found that a cat’s visual system is wired to work at birth but will atrophy or waste away if not used. Cats that did not use their eyes lost the neural connections in the visual cortex. Hubel and Wiesel concluded that cats had to use their eyes in order for brain cells in their visual cortex to maintain the connections that were present at birth. This was science’s first clear evidence of neural plasticity; because of their research, Hubel and Wiesel won the 1982 Nobel prize awarded for work in physiology or medicine.
Neural plasticity is the term used to explain that neural connections can be altered through experience. Plasticity refers to flexibility, and the main idea behind this concept is that that the brain works in accordance with the “use-it or lose-it” principle. Neural connections and pathways used over and over are strengthened, but connections and pathways never or seldom used atrophy and are lost. For example, the brain at birth is wired to hear evert phonemic sound in every human language. If children hear sounds from only one language, the pathways for the phonemes in that language are strengthened, but pathways for other phonemic sounds are lost. So an adult who was raised hearing only English will have difficulty hearing phonemes unique to Japanese or Russian because those neural connection were never stimulated and were lost. Moreover, that adult will hear a second language through the filter of his or her first language. This is why most adults who learn a second language speak it with an accent.
* Adapted from text: Shelley, Lynn M., and Bernard C. Beins. Student Handbook to Psychology: Developmental Psychology. Facts On File, 2012.
This text has 46 sentences, with 957 words (20.8 per sentence) with 1.54 syllables per word.
Flesch-Kincaid Grade Level: 10.6
This text has 46 sentences, with 957 words (20.8 per sentence) with 1.54 syllables per word.
Flesch-Kincaid Grade Level: 10.6
Comprehension and Reading Skills Quiz
If taking the online version of this quiz, please click through using the button below. It will automatically score itself when you finish. If you miss two or more questions, you should consider taking a Reading Skills lab to enhance your reading and study skills proficiency.