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.
Example: When information travels from the sense organs to the thalamus to the amygdala, people respond instantaneously, without thinking, to events in their environment. A parent may snatch her child away from a curb without thinking if she hears the sound of squealing tires coming toward them.
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.
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.
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.