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The Biological Bases of Emotion
The experience of emotion is accompanied by activation of two major areas of
the nervous system: the brain and the autonomic nervous system.
Activation of Brain Regions
The area of the brain known as the limbic system is highly
involved in emotion. One structure in the limbic system, called the amygdala, plays a particularly important role in regulating
emotion.
Researchers believe that sensory information about emotion-evoking
events moves along two pathways in the brain. The information goes
first to the thalamus and from there moves simultaneously to the amygdala
and the cortex of the brain. The amygdala processes the information quickly
and sends signals to the hypothalamus, which in turn activates the autonomic
nervous system. The cortex, on the other hand, processes the information
more slowly, allowing people to appraise or evaluate the event.
Activation of the Autonomic Nervous System
The autonomic nervous system controls all the automatic
functions in the body. See pages 51–52 for more information about the autonomic
nervous system.
When an emotion-evoking event happens, the sympathetic branch
of the autonomic nervous system, which prepares the body for action, begins to
work. It sends signals to the adrenal gland, which secretes the hormones
epinephrine and norepinephrine. These hormones in turn prepare a person to face
the challenges of the event. The following physical responses are indicative
signs in a man or woman:
- Blood pressure, heart rate, respiration rate, and blood sugar levels increase and prepare a person for action.
- Pupils dilate to let in more light for vision.
- The digestive processes slow down so that energy can be directed to the crisis at hand.
Measuring Emotion
Researchers often use autonomic responses to measure emotion. One
frequently used autonomic response is called the galvanic skin response. The galvanic skin response is an increase in the skin’s rate of
electrical conductivity, which occurs when subjects sweat during emotional
states. Researchers also use indicators such as blood pressure, muscle
tension, heart rate, and respiration rate to measure emotion.
Polygraph Tests
The polygraph, or lie detector, is a device
used to detect deception. In reality, the polygraph cannot detect deception.
Instead, it measures autonomic indices of emotion. A subject is hooked up to
the device and asked a series of neutral questions such as What is
your name? Where do you live? and so on. The polygraph records
the autonomic responses as the subject answers these questions, establishing
the baseline, or normal pattern of autonomic activation. Then the subject
answers other questions that can determine guilt or innocence, such as
Where were you on the night of the murder?
In theory, when lying, the subject feels emotions such as nervousness
or anxiety, and the polygraph records accompanying changes in autonomic
activation. In practice, the polygraph is not very effective. Polygraph
tests have a high error rate for two main reasons:
- Many people who are not engaging in deception feel nervous or anxious when asked questions concerning their guilt or innocence.
- People who are engaging in deception can often “trick” the polygraph by acting tense during neutral questions so that their baseline responses resemble their responses during the critical period of questioning.
Differences Among Emotions
The release of the hormones epinephrine and norepinephrine accompanies
many emotional states, but emotions differ at the biological level:
- Different emotions have different patterns of brain activation.
- Different neurotransmitters are involved in different emotions.
- Different emotions have different patterns of autonomic nervous system activity.
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