Emotion: The Biological Bases of Emotion

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?