What is the intraoperative use of following devise

This is bispectral index(BIS). The BIS monitor is the first quantitative EEG index introduced into clinical practice as a monitor to assess the depth of anesthesia. BIS technology measures only the hypnotic component of anesthesia. It consists of a sensor, a digital signal conveer, and a monitor. The sensor is placed on the patient's forehead to pick up the electrical signals from the cerebral coex and transfer them to the digital signal conveer. BIS technology is available as a stand-alone unit, or as a modular solution integrated into the manufacturer's monitoring system.