A standard polygraph records changes in blood pressure, pulse rate,
pulse strength, galvanic skin reflex (sweat gland activity), and upper and lower
breathing patterns. It does not matter if the subject is "nervous" during
the testing process - that is to be expected. The polygraph records significant
changes from the subject's "norm" when specific questions are asked.
A person intending deception to a particular question will activate his/her Sympathetic
Nervous System as a "self defense" mechanism when that question is asked
on the test. The SNS activation will cause recognizable changes in one or more
of the physical responses.