In 1848, Phineas Gage, a railway worker, was in a freak accident. He was using a tamping rod to pack sand and explosive powder into a drilled rock hole and actually managed to shoot that rod—over three feet long and some 13 pounds—into his head. He blinded one eye, but experienced little damage to his faculties.
Even so, his behavior changed. He went from a normally polite, thoughtful and conscientious man to being rude, feckless and socially inept. Five years after Gage’s death, Dr. John Harlow exhumed and examined his body. Dr. Harlow discovered that the prefrontal cortex of the brain not only controlled decision-making, but influenced a person’s temperament, as well.
You have probably seen the wrinkled mass of the brain in plastic sculptures or on television during medical autopsies, which are physical examinations of the dead. However, when we are infants, the cerebral hemisphere—the two front parts of the brain cerebrum—have smooth surfaces. As the brain develops, it folds in on itself, wrinkles and doubles over.
New life experiences cause more bulges and furrows, creating more hills and valleys in the brain, giving the “rind”—cortex—more room. If the brain was smoothed out, a human skull would be the size of an elephant’s skull!
Students of brain matter see a gray wrinkled mass. And truth is, the larger the cerebral cortex, the more brain cells inside. Comparatively speaking, our brain size is 1,000 times that of a rat.
Underneath the top layer is the white matter, which has communication filaments called axons and dendrites. This white matter is what allows one nerve cell, or neuron, to fire off to another. At full development, the human brain has 100 trillion neuronal connections and new ones are continually developed throughout our lives. These neuron axons and dendrites talk to each other by a series of electrical and chemical signals.
The connection between them is not a fusion of one neuron to another, but it is separated by a tiny space called the synapse.
Information for the brain is completed by the use of electricity that transforms into chemistry. This simplified explanation of the process goes like this: the chemical travels across the synapse where it links up with neuron receptors. A receptor is stimulated into a nerve cell and sends an electrical transmission. This transmission travels the length of the axon until it reaches the synapse where the chemical process takes over again. It is like: fire, shoot the space, link and fire up again.
According to neuroscientist John Morrison at Mt. Sinai Hospital, people with Alzheimer’s disease have a, “…loss of connecting neurons responsible for complicated functions requiring the integrated activity of the frontal, parietal and temporal cortices.”
Division of Labor
The cortex is divided into areas that complete different functions. For example:
- The prefrontal association cortex—just above your forehead—works on thought and perception
- The Broca’s area, a small area sandwiched in above the temple is for speech
- The limbic association cortex controls thought and perception, but it also accesses learning and emotions
- Short-term memory is just below the olfactory cortex which identifies smells
Perhaps that’s why the smell of macaroni and cheese is so reminiscent of a period of childhood, because we ate it every day in our seventh year of life!
- The premotor and motor cortex make connections for movement
- The sensory cortex talks to our brain about taste and touch, as does the Wernicke’s area, which heavily delves into sensory integration
- The auditory cortex is well-named as it accesses our hearing
- The visual cortex sends impulses for sight
- The posterior—or rear—elevation of the brain is called the posterior parietal cortex and its function is for associations
A brain cell knows what type of cell t will be by its neighborhood. Susan McConnell, a researcher at the Department of Biological Sciences at Stanford University conducted an experiment. Since neurons are born from the division of stem cells, they are progenitors—the ancestors or originators—of any kind of cell, blood, skin, bone or brain. McConnell took a stem cell, morphed it into a neuron and parked it in a developing brain. It migrated and took on the traits of its fellow neighbors. Scientists say this stem cell is now called “plastic,” because it hears signals from outside itself and gets instructions from fellow cells that help to tell it what to do. They refer to this as the “fate” of the cell.
When Ms. McConnell transplanted new brain cells waiting to take their migration, the transplanted version retained their original characteristics and did not become like their neighbors. It had already received genetic instructions about what to become.
The Cerebral Cortex
While we’ve only touched on a small part of what the cerebral cortex is and can do, German neurologist Korbinian Brodmann (1868-1918) mapped these functional areas. He helped to identify and number the different areas in the brains of humans, monkeys and other mammals. This ended the considerable confusion that existed in his time, and with thought, this may be the beginning of interest for you in the considerable study of the miraculous human brain.
- Korbinian Brodmann (1868-1918) and His Contributions to Mapping the Cerebral Cortex
- Image 1 Wikimedia Commons: Cerebral Lobes
- Connect to Me: Axons and Dendrites
- Restak, Richard, M. and David Grubin Productions, Inc. The Secret Life of the Brain. New York: The Dana Press and the Joseph Henry Press, 2001.
- Brain Connection: The Strange Tale of Phineas Gage
- Carter, Rita et al. The Human Brain Book. London: Dorling Kindersley Ltd., 2009.
- Image 2 Wikimedia Commons: Brain Areas