On the other hand, the brain is not divided up in an entirely rigid way. As a result, the brain constantly creates new neural communication routes and rewires existing ones. Neuroplasticity enables us to learn and remember new things and adjust to new experiences. The principles of neuroplasticity help us understand how our brains develop to reflect our experiences. For instance, accomplished musicians have a larger auditory cortex compared with the general population Bengtsson et al.
These observations reflect the changes in the brain that follow our experiences. Plasticity is also observed when there is damage to the brain or to parts of the body that are represented in the motor and sensory cortexes. When a tumour in the left hemisphere of the brain impairs language, the right hemisphere will begin to compensate to help the person recover the ability to speak Thiel et al.
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And if a person loses a finger, the area of the sensory cortex that previously received information from the missing finger will begin to receive input from adjacent fingers, causing the remaining digits to become more sensitive to touch Fox, These new neurons originate deep in the brain and may then migrate to other brain areas, where they form new connections with other neurons Gould, We have seen that the left hemisphere of the brain primarily senses and controls the motor movements on the right side of the body, and vice versa.
This fact provides an interesting way to study brain lateralization — the idea that the left and the right hemispheres of the brain are specialized to perform different functions. In this surgery, the region that normally connects the two halves of the brain and supports communication between the hemispheres , known as the corpus callosum , is severed.
As a result, the patient essentially becomes a person with two separate brains.
4.2 Our Brains Control Our Thoughts, Feelings, and Behaviour
Because the left and right hemispheres are separated, each hemisphere develops a mind of its own, with its own sensations, concepts, and motivations Gazzaniga, In their research, Gazzaniga and his colleagues tested the ability of W. The researchers had W. By doing so, they ensured that — because the two hemispheres had been separated — the image of the shape was experienced only in the right brain hemisphere remember that sensory input from the left side of the body is sent to the right side of the brain.
Gazzaniga and his colleagues found that W. On the other hand, W. This research, and many other studies following it, has demonstrated that the two brain hemispheres specialize in different abilities.
In most people the ability to speak, write, and understand language is located in the left hemisphere. This is why W. The left hemisphere is also better at math and at judging time and rhythm. It is also superior in coordinating the order of complex movements — for example, lip movements needed for speech. The right hemisphere, on the other hand, has only very limited verbal abilities, and yet it excels in perceptual skills. The right hemisphere is able to recognize objects, including faces, patterns, and melodies, and it can put a puzzle together or draw a picture.
That would be drastically oversimplifying the concept of brain differences. We normally use both hemispheres at the same time, and the difference between the abilities of the two hemispheres is not absolute Soroker et al. This fact is puzzling, in part because the number of left-handers is so low, and in part because other animals, including our closest primate relatives, do not show any type of handedness.
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The existence of right-handers and left-handers provides an interesting example of the relationship among evolution, biology, and social factors and how the same phenomenon can be understood at different levels of analysis Harris, ; McManus, At least some handedness is determined by genetics. But culture also plays a role. There are both advantages and disadvantages to being left-handed in a world where most people are right-handed.
One problem for lefties is that the world is designed for right-handers. Automatic teller machines ATMs , classroom desks, scissors, microscopes, drill presses, and table saws are just some examples of everyday machinery designed with the most important controls on the right side.
Despite the potential difficulty living and working in a world designed for right-handers, there seem to be some advantages to being left-handed. Throughout history, a number of prominent artists have been left-handed, including Leonardo da Vinci, Michelangelo, Pablo Picasso, and Max Escher. Left-handed people are also better at envisioning three-dimensional objects, which may explain why there is such a high number of left-handed architects, artists, and chess players in proportion to their numbers Coren, In sports in which handedness may matter, such as tennis, boxing, fencing, or judo, left-handers may have an advantage.
They play many games against right-handers and learn how to best handle their styles. Right-handers, however, play very few games against left-handers, which may make them more vulnerable. This explains why a disproportionately high number of left-handers are found in sports where direct one-on-one action predominates.
In other sports, such as golf, there are fewer left-handed players because the handedness of one player has no effect on the competition. At this point, however, this idea remains only a hypothesis, and determinants of human handedness are yet to be fully understood. Bengtsson, S. Extensive piano practicing has regionally specific effects on white matter development.
Nature Neuroscience, 8 9 , — Best, B. The amygdala and the emotions. Betancur, C. Association between left-handedness and allergy: A reappraisal. Neuropsychologia, 28 2 , — Bodmer, W. The book of man: The quest to discover our genetic heritage. London, England: Little, Brown and Company. Bower, J. Rethinking the lesser brain. Scientific American, , 50— Coren, S. The left-hander syndrome: The causes and consequences of left-handedness. The human cerebral cortex: Gender differences in structure and function.
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Science, , — Fritsch, G. Original work published Gazzaniga, M. Forty-five years of split-brain research and still going strong. Nature Reviews Neuroscience, 6 8 , — Observations on visual perception after disconnexion of the cerebral hemispheres in man. Brain, 88 2 , — Geschwind, N. Left-handedness: Association with immune disease, migraine, and developmental learning disorder.
Gibson, K. Evolution of human intelligence: The roles of brain size and mental construction. Brain Behavior and Evolution 59 , 10— Gould, E. How widespread is adult neurogenesis in mammals? Harris, L. Cultural influences on handedness: Historical and contemporary theory and evidence. Coren Ed. New York, NY: Elsevier. Hepper, P. Prenatal thumb sucking is related to postnatal handedness. Neuropsychologia, 43 , — Ida, Y. Cultural differences in side bias: Evidence from Japan and India. Laterality: Asymmetries of Body, Brain, and Cognition, 8 2 , — Jones, G. A note on Corballis and the genetics and evolution of handedness: Developing a unified distributional model from the sex-chromosomes gene hypothesis.
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Self-stimulation of the brain: Its use to study local effects of hunger, sex, and drugs. Positive reinforcement produced by electrical stimulation of septal area and other regions of rat brain. Journal of Comparative and Physiological Psychology, 47 , — Peters, M. Hand preference for writing and associations with selected demographic and behavioral variables in , subjects: The BBC Internet study.
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Brain and Cognition, 62 2 , — Sherman, S. In recent years, whole genome and transcriptome sequencing of clinical samples has revealed a number of molecularly distinct subtypes of medulloblastoma Jones et al. Disruption of transit amplification remains a compelling model for the Shh subgroup of tumours, based on experimental disruption of Shh signalling Goodrich et al.