To measure the resistance, a small voltage is applied to the skin and the skin's current conduction is measured. Skin conductance is considered to be a function of the sweat gland activity and the skin's pore size. An individual's baseline skin conductance will vary for many reasons, including gender, diet, skin type and situation. Sweat gland activity is controlled in part by the sympathetic nervous system. After a startle, the skin's conductance will decrease naturally due to reabsorption.
Excess sweat pours out of the duct.
Sweat gland activity increases the skin's capacity to conduct the current passing through it and changes in the skin conductance reflect changes in the level of arousal in the sympathetic nervous system. Increased GSR indicates a heightened sympathetic nervous system arousal. The Blood Volume Pulse Sensor The Blood Volume pulse sensor uses photoplethysmography to detect the blood pressure in the extremities. Photoplethysmography is a process of applying a light source and measuring the light reflected by the skin. The resulting pressure waveform is recorded.