This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.
Biology 202, Spring 2005
First Web Papers
Last month a Colorado man was admitted to the hospital after x-rays revealed a 4-inch nail wedged into the front portion of his skull, millimeters away from his optic nerve. After hours of surgery to remove the foreign object from this delicate portion of the brain, doctors assured friends and family that he would be pain-free and back to normal in no time (1). People nationwide agreed he was lucky to have missed all important areas of the brain. They wondered what would have happened to this unassuming construction worker if the nail had hit part of the functioning 10% of his brain. Or did he actually hit part of the 10%, and if so, is it a miracle that he survived? The world may never know...well, not necessarily.
For generations and generations and even among well-educated people today, a myth has circulated about the "useable" percentage of the brain; many argued, and still believe today that one only uses 10% of his or her brain. Recent studies have since provided overwhelming evidence to suggest that this theory is much more than 10% wrong.
The myth is thought to have originated from a few main sources. One such source is behaviourist psychologist Karl Lashley, who in the 1920s spent time executing experiments on lab rats to determine where in the cortex the neural bulge for memory was located (2). He first taught the rats how to complete a particular maze; he then proceeded to cut portions of their cortex away to determine the area that housed the function of memory. Instead of finding a distinct location, Lashley determined that memory seemed to be spread evenly throughout the layers of the cortex. This once misinterpreted concept is now understood as "'redundancy' and is found throughout the nervous system. Multiple pathways for the same function may be a type of "safety mechanism" should one of the pathways fail."(3)
With modern-day technology, former ambiguities such as these are now understood more thoroughly. Metabolic rates of particular sections of the brain can be mapped over time from different stimuli with such instruments as Functional Magnetic Resonance Imaging machines (fMRIs). "Today the entire brain is mapped in extensive detail, and a specific function has been found for each part of the brain."(4) This source goes on to explain that most functions of the brain reside on either the left or right portion of the brain (most functions are lateralized). One obvious exception, however, are the frontal lobes, where there is an extensive network of redundant structures. Over time, mapping and autopsy exploration have exposed a type of hierarchy of functioning portions of the brain. This is to say that over the course of the day one uses all of his or her brain, but at any given moment in time only part is being used depending on what task is being performed; some parts are also noticeably more metabolically active than others (5). For example, calculating a complicated algorithm will produce a completely different neural pattern than that generated while knitting a scarf. One then naturally wonders, what happens when particular portions of the brain are deformed, or altered in some way? Do these neural pathways find a new route to complete a particular function, or does the function simply not transpire due to an incomplete processing signal? What about other organisms and their lack or presence of particular portions of the human brain?
In January of 2005, Pediatric News published the results of a study on the brains of children diagnosed with Attention Deficit Hyperactivity Disorder (ADHD). This study provided evidence that portions of the frontal cortex, basal ganglia, brainstem, and cerebellum of children diagnosed with ADHD are significantly smaller than normal. The study also provided evidence that such physical and behavioral abnormalities are less pronounced in children who have received pharmaceutical intervention (6) (7). The change in function of the brain is thought to be caused by the extensive remyelination of axons in treated individuals; in other words, the brain grows and changes into a more socially accepted functioning brain.
One could conclude from this study that increased volume, or mass, of the brain means increased complexity and integration of function. Tracing the size and complexity of the brain through time, one distinguishes a general trend of increased complexity and mass of neuroanatomy (8). Even though the cerebrum of many mammals has enlarged over time, a progressively smaller proportion of it correlates with motor/sensory duties. While elephants and some whales have larger brains than humans, evidence does not support the theory that they exhibit a more sophisticated level of reasoning. Given the high demand for motor and sensory requirements to integrate movement in the bodies of these immense organisms, bigger brains are naturally essential. Also, bigger brains are not necessarily an evolutionary advantage; since they require such extensive nourishment, they have the possibility of overheating and organisms must find solutions to this problem with mechanisms to diffuse heat without sacrificing a significant amount of energy.
This, however, is not the whole story. Not only is it important to note the differences in body size of animals and their varied neural metabolic rates, it is also imperative to trace the percentage of neocortex present in the brains of differing species. "Neocortex enhances both the capacity to make use of variability in behavior and the capacity to deal with resulting ambiguities and uncertainties."(9) Examples of such ambiguities reside in differing interpretations of sensory input. Whereas monkeys and humans are thought to have over 50 differentiated neocortical areas, small-brained mammals characteristically have about 15 (10). Not only do different species establish differing responses to external stimuli, but individuals within species exhibit such ambiguities as well; a child with ADHD may respond differently to a loud classroom than a physiologically "normal" child. Even over time, humans are said to lose the function of 100,000 neurons each day after the age of 30; the "useable" size of their brains is therefore forever decreasing.
So is the Colorado man lucky? Well, yes of course, for he most likely hit a "useable" portion of his brain and is lucky to still be alive. It will be interesting to follow the story to determine if because of the altered shape of his brain, noticeable behavioral differences will later ensue.
1)MSNBC, Man Survives 4-inch Nail in Skull.
2)Science and Consciousness Review, Exploiting the 10 Percent Myth.
3)Washington.edu faculty page, Neuroscience for Kids - 10% of the Brain Myth.
4)The New England Skeptical Society, Don't You Believe It: 90% of the Brain is a Terrible Thing to Waste.
5)Urban Legends Reference Page, The Ten-Percent Myth.
6)Thomson Learning, InfoTrac College Edition
7) Pediatric News, Jan 2005 v39 i1 p7(1)
8)University of Claifornia San Diego - user: jmoore, Allometry.
9)Serendip Website, Brain size and evolution.
10)nature.com, Evolutionary neurobiology: The neocortex comes together.
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