Polygraph: How it works

  • The polygraph is an electronic instrument that measures a person’s physiological reactions to stress. The polygraph technique is based on our bodies’ fight-or flight response to stressful situations (the stimulation of the sympathetic nervous system).


  • When we feel threatened, internal changes occur throughout our bodies, and the polygraph monitors several of those changes (heart rate, blood pressure, breathing, and sweat gland activity).


  • In a well-run polygraph there are several different types of questions. Sophisticated numerical evaluation of polygraph charts is the basis for decisions of deception or truthfulness.