The Galvanic Skin Response measures the skin’s conductance between two electrodes. A person’s skin conductance is a function of sweat gland activity and the skin’s pore size. Sweat gland activity is affected by various factors including skin type, diet, gender and situation. An embarrassing question would trigger a level of cortical arousal that results in a very quick change in sweat gland activity (0.2 to 0.5 seconds), causing a sharp drop in skin resistance. Advanced layers of the cortex in humans are linked to the forefinger and thumb, thereby producing significant GSR upon stimulus.
Here are some websites that we used to find this information and make our own GSR sensors:
http://www.trans4mind.com/psychotechnics/gsr.html
http://www.plazaearth.com/usr/gasperi/gsr.htm