Rheoencephalography (REG) a technique [1] of continuous registration of cerebral blood flow. An electronic device called a rheoencephalograph is used in rheoencephalography. [2] Electrodes are attached to the cranium at specific points on the head and allow the device to continuously measure the electrical conductivity of the tissue located between the electrodes. A rheoencephalograph is also used for brain blood flow biofeedback. [3]