The brain’s left and right hemispheres are almost mirror images, each controlling and responding to messages from the other side of the body. Yet, the two hemispheres work in slightly different ways.
Imagine a pair of twins who have lived together all their lives, sharing every thought, sensation, and emotion through continuous dialogue. Each of them is capable of doing nearly everything the other can do, but they also have individual strengths – when faced with a task, the one that is better at that sort of thing automatically takes the leading role.
The brain probably evolved as two similar halves so that there was a ‘spare’ brain to take over if one was damaged. However, as humans developed more skills, space started to run out. Nature found a way around this problem by placing some of the newfound abilities in just one hemisphere rather than doubling up.
Sensory information from each side of the body enters the brain and then crosses over to the opposite hemisphere. Similarly, signals from each hemisphere cross over to control the other side of the body. When you raise your right hand, it is your left hemisphere that controls it.
At birth, both hemispheres contain all that is required to develop every mental skill – a young child could lose an entire hemisphere and still develop normally because the remaining one will do the work of a whole brain. However, minor differences between the hemispheres make each one best suited to particular tasks, and, over time, the differences become so entrenched that the loss of a hemisphere in later life is catastrophic.
Left-Right Differences
On the whole, the right hemisphere is good at making out ‘wholes,’ such as grasping an emotion, and the left is better at analyzing things, such as tackling a math problem. In practice, nearly everything in our minds is the result of both right and left-hemisphere processing. Understanding a joke, for example, involves following the plot (a left-hemisphere function) and ‘getting’ the point (a right-hemisphere specialist).
The most obvious difference between the hemispheres concerns language. In nearly all right-handed people and some left-handers, language is processed entirely by the left hemisphere. Hence, a stroke in the left hemisphere may well cause language problems, while a right-hemisphere stroke is likely to affect the sense of where things are.
Language is crucial to our thoughts because most of our thinking is done in the form of words. While both hemispheres contribute to our perceptions, only the left hemisphere reports them. If you look at a picture, the right hemisphere will tend to interpret the content intuitively – the colors may provoke a feeling not expressed in words. By contrast, the left hemisphere will recognize the colors as ‘red,’ ‘blue,’ and so on but will not be so moved by them emotionally. Normally, the right hemisphere will transmit its feelings about the picture to the left hemisphere, which then incorporates this information into its view before turning the overall perception into words.
However, the left hemisphere may misinterpret what the right tells it, as the information received will be interpreted according to how the left hemisphere sees the situation. If the left hemisphere is not aware of a threat, for example, it may report ‘fear’ messages from the right hemisphere as ‘excitement’ instead. The two hemispheres work together to make the best judgments about the threats and opportunities that confront the person.
