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Left and Right Brain

Explanations > Brains > Parts of the Brain > Left and Right Brain

Two hemispheres | Splitting the brain | Left brain | Right brain | Other stuff | So what?

Much has been written about left and right brains. Are they two different brains? Two personalities? Two parts of the same person? Here are some notes and thoughts.

Two hemispheres

The brain cortex (the crinkly 'walnut' bit) is divided into two clear hemispheres, connected by the corpus callosum, which provides an 'information highway' between them.

The halves are neither mirror images nor contain completely exclusive functions. However there are significant similarities. Each half receive sensory information though, curiously, from the opposite side of the body. Thus the right eye goes to the left brain and vice versa. The exception is the nose: the right nostril goes to the right brain.

Lateralized functions, on the other hand, are located primarily in one hemisphere. The dominant hemisphere for most right-handed people this is the left hemisphere. For many left-handed people there is a reversal, and the dominant hemisphere is on the right. When we talk about the 'left brain', we usually actually mean the dominant hemisphere.

Splitting the brain

A radical operation to separate the two halves is sometimes used to treat extreme forms of epilepsy. Studies of separated-hemisphere patients gave early understanding of differences.

A split-brain person on the surface may seem quite normal, yet they will also display some very interesting behaviors.

Roger Sperry won the Nobel Prize in 1981 for his work in this area. Michael Gazzaniga, one of Sperry's students, developed this understanding further.

Left brain

The left brain (or dominant hemisphere) has a focus in analysis, extracting individual elements of experience. It is good at recognizing serial events.

The left brain also controls speech. If the left brain is damage or something is shown to the right eye of a split patient, the person may recognize the item but cannot name it. When thinking is verbal, it can seem that the conscious mind is in the left brain.

Some of the strange effects that can be seen in split-brain people include:

• The left hand will put down a book that is being enjoyed by the verbal left brain, because it does not stimulate the right brain, which controls the left hand.

• The left hand may surprisingly make obscene gestures as it reflects right-brain emotion.

Consciousness is often associated with the left brain as the verbal areas allow us to put perception into words.

Right brain

The right brain has a focus in synthesis, putting together elements to understand the whole. The ability to understand maps and draw pictures is thus a right-brain activity.

It is typically thought of as being 'creative' in contrast to the left-brain's language-driven logic.

Some of the effects that can be seen in split-brain people include:

• Show a spoon to just the left eye and the person cannot name it, but they can draw it.

• Apply a smell to the right nostril and they say they smell nothing.

• Show the command 'laugh' to the right eye and the person laughs, but does not 'know' why they did so.

The right brain also manages temporal and spatial relationships and analyzes nonverbal information. It is also used in communication of emotion.

Other stuff

Much has been said about left and right brains and not all of this is proven. Here's some of the notions proposed:

Parting hair on the left is said to emphasize masculine traits as it draws attention to left-brain activities; similarly, parting on the right is said to emphasize feminine traits.

See also

Gazzaniga, M.S., Bogen, J. E., and Sperry, R. W. (1962) Some functional effects of sectioning the cerebral commissures in man. Proceedings from the National Academy of Science, 48, Part 2, 1765-1769

Sperry, R. W. (1966). Brain bisection and mechanisms of consciousness. In J.C. Eccles (Ed.) Brain and consciousness experience. Heidleberg: Springer-Verlag