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Brain Organization and Learning

Functional specialization has led to the development of traits that are uniquely human, such as different learning styles and sophisticated spoken and written languages. These remarkable traits rely heavily on memory systems and transfer. Thus, an understanding of how memory and transfer work is needed in order to understand better the nature and impact of brain specialization on learning.

BRAIN LATERALIZATION

One of the intriguing characteristics of the human brain is its ability to integrate disparate and seemingly disconnected activities going on in specialized areas of the brain into a unified whole. Brain scans reveal how certain areas of the brain get involved in processing and performing specific tasks. For example, the auditory cortex responds to sound input, the frontal lobe to cognitive rehearsal, and sections of the left hemisphere to spoken language. The ability of certain areas of the brain to perform unique functions is known as cerebral specialization. If the activity is mainly limited to one hemisphere, it is called cerebral lateralization.

As evidence continues to accumulate regarding specialized brain areas, neuroscientists have had to modify their theories of brain organization accordingly. Researchers are now endorsing the idea that the brain is a set of modular units that carry out specific tasks. According to this modular model, the brain is a collection of units that supports the mind’s information processing requirements (a speech module, a numerical computation module, a face recognition module, etc.) and not a singular unit whose every part is capable of any function (Gazzaniga & Miller, 2009; Rose, 2005).

The first indications of brain lateralization were discovered long before scanning technologies were developed. During the late 1950s, neurosurgeons decided that the best way to help patients with severe epileptic seizures was to sever the corpus callosum, the thick cable of more than 200 million nerve fibers that connects the two cerebral hemispheres. This last-ditch approach isolated the hemispheres so that seizures in the damaged hemisphere would not travel to the other side. The surgery had been tried on monkeys with epilepsy, and the results were encouraging. By the early 1960s, surgeons were ready to try the technique on human beings. One of the pioneers was Dr. Roger Sperry of the California Institute of Technology. Between 1961 and 1969, surgeons Joseph Bogen and Phillip Vogel successfully performed several operations under Sperry’s guidance.

Although the operations resulted in a substantial reduction or elimination of the seizures, no one was sure what effect cutting this bridge between the hemispheres would have on the “split-brain” patients. Sperry and his student Michael Gazzaniga conducted experiments with these patients and made a remarkable discovery. Splitting the brain seemed to result in two separate domains of awareness. When a pencil was placed in the left hand (controlled by the right hemisphere) of a blindfolded patient, the patient could not name it. When the pencil was shifted to the right hand, however, the patient named it instantly. Neither hemisphere seemed to know what the other was doing, and they acted, as Sperry (1966) said, “each with its own memory and will, competing for control.”

As the tests progressed, Sperry charted the characteristics each hemisphere displayed. He concluded that each hemisphere seems to have its own separate and private sensations, its own perceptions, and its own impulses to act. This research showed that the right and left hemispheres have distinctly different functions that are not readily interchangeable. It also solved the mystery of the corpus callosum. Its purpose is largely to unify awareness and allow the two hemispheres to share memory and learning. Sperry won the 1981 Nobel Prize in medicine in part for this work.

Left and Right Hemisphere Processing (Laterality)

Continued testing of split-brain patients and brain scans of normal (whole-brained) individuals have revealed considerable consistency in the different ways the two halves of the brain store and process information. This cerebral separation of tasks is referred to as laterality. The results of numerous studies on laterality continue to provide more insights into the kind of processing done by each hemisphere and expand our understanding of this remarkable division of labor.

Left Hemisphere

The left brain monitors the areas for speech in most right-handed people. Some left-handed people have their speech centers in the right hemisphere (Duffau, Leroy, & Gatignol, 2008). The left hemisphere understands the literal interpretation of words, and recognizes words, letters, and numbers written as words (Ellis, Ansorge, & Lavidor, 2007). It is analytical, evaluates factual material in a rational way, perceives the detail in visual processing, and detects time and sequence. It also performs simple arithmetic computations (Zamarian, Ischebeck, & Delazer, 2009). Arousing attention to deal with outside stimuli is another specialty of the left hemisphere, and it appears to process positive emotions such as joy (Hecht, 2010).

Right Hemisphere

The right brain gathers information more from images than from words, and looks for visual patterns. It interprets language through context—body language, emotional content, and tone of voice—rather than through literal meanings (Campbell, 2006). It specializes in spatial perception; recognizes places, faces, and objects; and focuses on relational and mathematical operations, such as geometry and trigonometry. This hemisphere also appears to process negative emotions such as sadness and depression (Hecht, 2010).

References:

Campbell, S. (2006). Language in the nondominant hemisphere. In K. Brown(Ed.), Encyclopedia of language and linguistics (2nd ed., pp. 529-536). Oxford, UK: Elsevier.

Duffau, H., Leroy, M., & Gatignol, P., (2008). Cortico-subcortial organization of language networks in the right hemisphere: an electrostimulation study in left-handers. Neuropsychologia, 46, 3197-3209.

Ellis, A. W., Ansorge, L.,  & Lavidor, M. (2007). Words, hemispheres, and dissociable subsystems: The effects of exposure duration, case alternation, and continuity of form on word recognition in the left and right visual fields. Brain and Language, 103, 292-303.

Gazzaniga, M. S., & Miller, M. B. (2009). The left hemisphere does not miss the right hemisphere. The Neurobiology of Consciousness, 261–270.

Hecht, D. (2010). Depression and the hyperactive right-hemisphere. Neuroscience Research, 68, 77–87.

Rose, S. (2005). The future of the brain: The promise and perils of tomorrow’s neuroscience. New York: Oxford University Press.

Sperry, R. (1966). Brain bisection and consciousness. In J. Eccles (Ed.), How the self controls its brain. New York: Springer-Verlag.

Zamarian, L., Ischebeck, A., & Delazer, M. (2009, June). Neuroscience of learning arithmetic: Evidence from brain imaging studies. Neuroscience & Biobehavioral Reviews, 33, 909–925.

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