Question

Lie detector tests are used in our society by law enforcement agencies to help determine the guilt or innocence of a suspect. The basis of these exams is to assess the body’s reaction to stress via our sympathetic division of the autonomic nervous system. The effects of the sympathetic nervous system are widespread. Pick one gland, organ, or system that is affected by the sympathetic nervous system, describe the physiology of its actions on the chosen structure/system, and how the lie detector test assesses these changes.

Answer 1

Lie detector or polygraph machine is a bunch of medical devices that assesses changes in our respiratory system, cardiovascular systems and skin conductivity during stressed condition. These systems are automatically controlled by sympathetic nervous system during stress. Stress like situation arises when someone is telling a lie, as lie is much harder for brain to create than just telling the truth. So changes in those systems are monitored and recorded. Any variance of the recorded data tells about a stress response which can be related to the asked question at that moment.

One of the organ systems that polygraph tests rely on is cardiovascular system. Heart rate and blood pressure is monitored during the test. Heart is the major organ that pumps blood in our body. Pumping of heart ensures that each tissue in our body is receiving blood for nutrients and oxygen and excreting metabolic waste. A heart beats about 60 to 100 times per minute which is an average range for a healthy normal adult in resting state. Blood is circulated via blood vessels. Arteries carry oxygenated blood whereas veins carry deoxygenated blood. Blood while travelling inside vessels, exerts a force on the vessel wall which is the blood pressure.

Sympathetic nervous system (SNS) responds to stress. It generates ‘fight or flight’ response during the time of stress. SNS creates this response by stimulating adrenal glands to produce adrenalin hormone which increases heart rate. Heart muscle upon receiving the signal beats faster. It constricts and pumps more blood into circulation and increasing the cardiac output. The heart rate may increase above 100 beats per minute during stress. Increased cardiac output increases blood pressure. The changes in stress response is more prevalent for acute stress, like sudden incident.

Lie detector measures the changes in heart rate and blood pressure. An acute stress condition may arise if the person feels uneasy as he/she is trying to construct lies. As it is mentioned, construction of lie is harder for brain than just telling the truth, it produces stress on brain and sympathetic nervous system acts on that. Heart rate and blood pressure is increased in process of it. The changes are seen clearly on recording devices like electrocardiogram in real time. Finally a inference is taken about the effect of the asked question on the person.