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LAB 9 - The Autonomic Nervous System and Polygraphy


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The peripheral nervous system is divided into the somatic nervous system, which controls organs under voluntary control (mainly muscles) and the autonomic nervous system, which regulates individual organ function and homeostasis, and for the most part is not subject to voluntary control.

Autonomic Nervous System

polyani.gif (4447 bytes)The Autonomic Nervous System is most important in two situations, those emergency situations that cause stress and require us to "fight" or take "flight" (run away) and those non-emergency situations that allow us to "rest" and "digest". The autonomic nervous system consists of sensory neurons and motor neurons that run between the central nervous system (especially the hypothalamus and medulla oblongata) and various internal organs such as the brain, lungs, viscera, glands (both exocrine and endocrine). The autonomic nervous system is responsible for monitoring conditions in the internal environment and bringing about appropriate changes in them. There are two major components of the autonomic nervous system, the sympathetic and the parasympathetic systems.

The autonomic NS consists of small diameter axons, which supply the visceral organs (stuff you cannot consciously regulate like hearts, guts, glands, etc.). For the case with somatic motor neurons, it takes two efferent neurons for the autonomic NS to get from the CNS to the effector cells. Effector cells are cells, which can do something when instructed (e.g., cardiac, smooth and skeletal muscle, and all gland cells).


polyani.gif (4447 bytes)The autonomic NS is used for lie detection tests known as polygraphs. In this lab we ran a simple lie detector exam to demonstrate the autonomic nervous systems role in lie detection. A full scale, conventional lie detection exam hooks you up to a physiological recorder to monitor functions controlled by the autonomic NS, but most specifically actions set off by mass discharge of the sympathetic NS when the subject has an emotional response associated with the telling of a falsehood. The sympathetic NS tends to fire off all at once (flight or fight response) in such situations and all sorts of physiological functions are altered. For example, heart rate goes up, pattern of respiration changes, blood pressure goes up, and production of sweat by glands in the skin of the hand goes up. We used a device called a Galvanic Skin Response (GSR) amplifier to monitor the production of sweat by the glands in the skin of the hand.. To monitor the GSR we placed two electrodes on the hand. One was wrapped around the finger of the subject without use of conductive cream, and the second was attached to the wrist of the subject with the use of conductive cream. The GSR passes a small current through the tissues of the hand. The amount of current passing is dependent primarily on the electrical resistance under the finger electrode. When the sympathetic NS discharges after any question, but particularly in response to a critical question, sweat production goes up, the electrical resistance of the skin goes down, more current flows, and a peak is registered on the recorder.


polyani.gif (4447 bytes)The subject gets hooked up to GSR. Then the subject picks a number between 1 and 10 in front of witnesses, however, the examiner must be absent. The examiner then is let back into the room and must determine the number picked my the subject by asking the subject questions answerable with a yes or no. A sample question might be, "was the number 1?" and so on. The subject must answer truthfully or it will be detected by the polygraph machine. The examiner checks the chart readout looking for peaks of tension, which are larger responses. The examiner might be required to run through the series of numbers more than once in order to check for consistency.  

Here are some pictures of my lab section performing this experiment.


polyani.gif (4447 bytes)Two metal plates that are attached on the ring and index finger, conductive cream, and a polygraph machine.

Polygraph machine

A polygraph is an instrument that simultaneously records changes in physiological processes such as heartbeat, blood pressure, and respiration. The underlying theory of the polygraph is that when people lie they also get measurably nervous about lying. The heartbeat increases, blood pressure goes up, breathing rhythms change, perspiration increases, etc. A baseline for these physiological characteristics is established by asking the subject questions whose answers the investigator knows. Deviation from the baseline for truthfulness is taken as sign of lying.

Finger Electrodes


polyani.gif (4447 bytes)Here are the results from of polygraph test from two different subjects in my lab. The first picked the number eight; however, somehow the subject fooled the machine because the results were unclear. The second subject, however, picked the number nine and as you can see on the graph below there is an obvious fluctuation in the graph every time the subject was asked if the number was nine.