The Left versus the Right Sides of the Brain: Their Impact on Learning
The higher brain – the cerebral cortex – is anatomically divided into two hemispheres – the right and the left. Although the two hemispheres are basically similar in structure, microscopic differences exist, and their functional abilities and propensities are different. These functional differences are described as ‘hemispheric asymmetry’ (Hellige, 1993). The left hemisphere controls sensory and motor functions of the right side of the body, and vice versa. The layman’s percept is that the left hemisphere is responsible for symbolic processes, production and perception of language, and rational thinking, while the right is involved in artistic, intuitive, and creative thinking. This paper shall focus on the differences between the two hemispheres in the learning process.
‘Learning’ is the process of acquiring new information by the nervous system, which is observable through changes in behavior. ‘Memory’ is the encoding, storage, and retrieval of learned information (Purves et al, 2004). Experiments over the last several decades have made it clear that the left hemisphere enables faster and more effective learning in some areas of cognitive ability, while the right hemisphere allows better learning of other aspects.
For reasons not well understood, the division of functions between the two hemispheres is essential for learning. For example, animal studies show that an association between a spatially biased movement and a reward cannot be learned in the absence of a strong side preference (Hellige, 1993). However, both hemispheres are not isolated from each other, and information is exchanged through nerve fibres that pass in the corpus callosum (Barrett, Barman, Boitano and Brooks, 2010).
Dominance is used to describe greater activity or use of one hemisphere (Barrett et al., 2010). If one hemisphere is dominant for hand use, it also tends to be dominant for language functions (Hellige, 1993), and sequential-learning tasks (Barrett, Barman, Boitano and Brooks, 2010).
In 96% of the population, the left hemisphere is dominant and controls the learning, processing and interpretation of language and speech (Hellige, 1993). The posterior superior temporal lobe in the left hemisphere is designated as Wernicke’s area, which controls the understanding of speech. The posterior inferior frontal lobe is defined as Broca’s area, which is responsible for generating words and fluent speech (Purves et al, 2004). These concepts are corroborated by anatomical findings. The ‘planum temporale’, an area in the superior temporal gyrus concerned with language-related auditory processing, is usually larger on the left side than the right. Other portions of the upper temporal lobe on the left side are also larger in right-handed individuals. In schizophrenic patients, the degree of reduction in volume of the left temporal gyrus correlates with the degree of disordered thinking (Purves et al, 2004).
The right hemisphere, on the other hand, is involved in learning the pragmatic aspects of language, such as understanding metaphors and humor. For example, the literal meaning of ‘warm’ as temperature would be held in the left hemisphere, while its more abstract understanding as a human emotion would be held in the right hemisphere. The right hemisphere is thus responsible for the ‘coloring’ of speech. Further evidence of this lateralization of language functions is with dyslexia. Dyslexia is a learning disability with impairment in learning to read. It is 12 times more common in left-handers than right-handers, and researchers conclude that some fundamental abnormality in the left hemisphere in these patients leads to the language learning impairment, and causes switching of major hand functions to the right hemisphere, resulting in left-handedness. Acquired dyslexia also occurs after left-brain damage (Barrett et al., 2010).
The left hemisphere is also predominant in visual-discrimination learning, and has been demonstrated to be superior to the right in learning and executing a sequence of movements, such as copying hand postures, (Hellige, 1993). Learning and execution of mathematical skills is also localized to the left hemisphere. Additional academic skills attributed to left hemisphere functioning include handwriting, learning symbols including letters and numbers, reading, phonics, and following directions.
The right hemisphere is important in learning to recognize different faces, by storing visual input in the inferior temporal lobe. The right hemisphere is also identified for learning spatial and navigational skills – the right hippocampus, for example, is concerned with learning where things are located (Barrett et al., 2010). The academic skills found to depend on the right hemisphere include haptic awareness, where objects are recognized through touch alone. It also includes shape and pattern recognition, sensitivity to color, learning music and singing, and expressing feelings and emotions (Major, 2012).
Memory involved with learning is stored in different areas of the brain. Researchers have found that different types of memories are stored in the left versus the right hemisphere, imparting credibility to the concept of their different functions. For example, experiments using implanted electrodes have shown that when individuals recall words, activity in their left frontal lobe and their left parahippocampal cortex increases. However, recall of pictures or scenes occurs with increased activity in the right frontal lobe, and in the parahippocampal cortex on both sides (Barrett et al., 2010).
The understanding of the differential roles of the left and right hemispheres in learning is essential to the management of children with learning disabilities. For example, children who early in life show failure in learning to read through the traditional process may be right-dominant, which occurs in about 4% of the population (Hellige, 1993). The traditional language teaching technique favors left-dominant children, who start learning language by first learning symbols (letters) and advancing step-by-step. Right-dominant children, on the other hand, learn language better by starting with touch, using the senses, and body movement. The right hemisphere cannot adapt to the step-by-step approach, and learns by finding patterns in random stimuli. Right-dominant people are also more comfortable in expressing through non-verbal approaches, such as by pictures, or typing/writing. Left-dominant people, are on the other hand, primarily verbal (Major, 2012).
Overall, specific learning functions and skills can be localized to either the left or right hemisphere, and one hemisphere of the brain is predominantly involved in carrying out any learned behavior. At the same time, it is important to recognize that intact functioning of both hemispheres is essential for completing all aspects of learning, memory and behavior. Even right-dominant individuals have some brain activities primarily controlled by the right hemisphere, and vice versa (Major, 2012). Therefore, no individual utilizes solely one hemisphere for the learning process.
References
Barrett, K. E., Barman, S. M., Boitano, S., Brooks, H. L. (2010). Learning, Memory, Language, & Speech. In: Ganong's Review of Medical Physiology, 23rd e (Chapter 19). Retrieved from: http://accessmedicine.com/content.aspx?aid=5241276
Hellige, J.B. (1993). Hemispheric Asymmetry: What's Right and What's Left. Cambridge, MA: Harvard University Press.
Major, S. (2012). The Impact of Hemispheric Dominance on Learning to Read. Retrieved from: http://www.homeeddirectory.com/blog/impact-hemispheric-dominance-learning-read
Purves, D., Augustine, G. J., Fitzpatrick, D., Hall, W.C., LaMantia, A-S., McNamara, J.O., Williams, S.M. (Eds). (2004). Neuroscience, 3rd e. Sunderland, MA: Sinauer Associates, Inc.
