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Hemispheric Differences in Expression of Emotion

Before scientists realized it was mostly the amygdala on the right side of the brain that regulated emotion, they noticed a difference between emotional processing of the left and right hemispheres.

What are different aftereffects of damage to the right hemisphere?

If the left hemisphere of the brain is damaged, leaving the right half in charge, a patient is likely to show a generally gloomy outlook on life, with seemingly unjustified feelings of anger, guilt, and despair. He or she may even burst into tears on occasion without knowing why. When the right half is excluded from control of behavior-by injury, surgery, or an epileptic attack-a patient is likely to be cheerful, even elated, and surprisingly indifferent to this abnormal state. (Kinsbourne, 1981)

The most compelling evidence for hemispheric differences in processing emotions comes from the Wada test. The Wada test is done before brain surgery. One hemisphere then the other is put to sleep by injecting anesthetic into major arteries supplying one side or the other. This is a temporary and reversible state that allows neurosurgeons to find out (for example) which side supports language.

What is some evidence from the Wada Test?

When the right hemisphere is anesthetized but the left is normal and awake, so the amygdalar region on the right is not active, patients show a "euphoric-maniacal" reaction characterized by laughter and joking. They seem "indifferent" to medical dangers-the thought of having brain surgery the next week does not bother them. By contrast, when the left hemisphere is anesthetized and the right is left awake, the patient is likely to show a "depressive-catastrophic" reaction. This is characterized by pessimism, worrying, and crying (Terzian & Ceccotto, 1959).

What was Kinsbourne's speculation?

Kinsbourne pointed out that left/right differences run parallel to an important dimension of decision-making for any animal: approach or avoidance. The hemispheres are like a control mechanism, one pushing (encouraging approach behaviors), the other pulling (encouraging avoidance behaviors). In normal operation the system is fine-tuned, striking an appropriate balance. In depression or its opposite, mania, the control mechanism is thrown out of balance. In the bipolar disorder ("manic-depression") the system oscillates wildly between the two extremes.

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