Piero Scaruffi(Copyright © 2013 Piero Scaruffi | Legal restrictions )
These are excerpts and elaborations from my book "The Nature of Consciousness"
Since the “split-brain” studies carried out in the 1950s by the US psychologist Roger Sperry, it has been held that the two hemispheres control different aspects of mental life (Konstantin Bykov had already proved this in Russia in 1924): the left hemisphere is dominant for language and speech, the right brain excels at visual and motor tasks and may also be the prevalent source of emotions. This is due to the fact that the two hemispheres are not identical. For example, the speech area of the cortex is much larger in the left hemisphere. The roles of two hemispheres are not so rigid, though: a child whose left hemisphere is damaged will still learn to speak and will simply use the right hemisphere for language functions.
Just like it dominates in language, the left hemisphere also dominates in movement. Both hemispheres organize movement of limbs (each hemisphere takes care of the limbs at the opposite side of the body), but the left hemisphere is the one that directs the movement and that stores the feedback (the one that learns skills/ habits). If the two hemispheres are separated, the right limbs keep working normally, but the left limbs become clumsy and are often unable to carry out even simple learned skills like grabbing a glass.
Brain asymmetry is not uncommon in other species, but handedness (that individuals always prefer one hand over the other) is uniquely human, and handedness appears to depend on the asymmetry of the hemispheres.
The main “bridge” between the two hemispheres is the corpus callosum, but a number of other “commissures” (communication channels) exist, and their purpose is not known.
The US psychologist Ross Buck proposed a decomposition of human behavior that mirrors the “behavior” of each hemisphere. In his view, our behavior is the product of several systems of organization which belong to two big families. The first one is the family of innate special-purpose processing systems (reflexes, instincts, etc.). In general their function is "bodily adaptation" to the environment. In general, their approach is not analytic but holistic and syncretic: they don't "reduce" the situation to its details, they treat it as a whole. In Buck's view, these processes are innate, we don't need to learn them. The second family contains acquired general-purpose processing systems. In general their function is to make sense of the environment. Their approach is sequential and analytic. The former family is associated with the right hemisphere of the brain and is responsible for emotional expression; the latter is associated with the left hemisphere and is responsible for symbolic thinking. The two families cooperate in determining the body's behavior.
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